





document Arr r. OF thi«? 



DECLASSIFIED 
By authority Secretary of 

SEP 30 1960 

Defense memo 2 August 1960 


LIBRARY OF CONGRESS 



SUMMARY TECHNICAL REPORT 
OF THE 

NATIONAL DEFENSE RESEARCH COMMITTEE 


DECLASSIFTED 
By authority Secretary of 

SEP 30 1960 

Defense memo 2 August 1960 
LIBRARY OF CONGRESS 


This document contains information affecting the national defense of 
the United States within the meaning of the Espionage Act, 50 U. S. C., 
31 and 32, as amended. Its transmission or the revelation of its con- 
tents in any manner to an unauthorized person is prohibited by law. 

This volume is classified in accordance with security regu- 

lations of the War and Navy Departm ents because certain chapters 
contain material which was at the date of printing. Other 

chapters may have had a lower classification or none. The reader is 
advised to consult the War and Navy agencies listed on the reverse of 
this page for the current classification of any material. 



Manuscript and illustrations for this volume were prepared 
for publication by the Summary Reports Group of the 
Columbia University Division of War Research under con- 
tract OEMsr-1131 with the Office of Scientific Research and 
Development. This volume was printed and bound by the 
Columbia University Press. 

Distribution of the Summary Technical Report of NDRC 
has been made by the War and Navy Departments. Inquiries 
concerning the availability and distribution of the Summary 
Technical Report volumes and microfilmed and other refer- 
ence material should be addressed to the War Department 
Library, Room lA-522, The Pentagon, Washington 25, D. C., 
or to the Office of Naval Research, Navy Department, Atten- 
tion : Reports and Documents Section, Washington 25, D. C. 

Copy No. 

83 


This volume, like the seventy others of the Summary Tech- 
nical Report of NDRC, has been written, edited, and printed 
under great pressure. Inevitably there are errors which have 
slipped past Division readers and proofreaders. There may 
be errors of fact not known at time of printing. The author 
has not been able to follow through his writing to the final 
page proof. 

Please report errors to : 

JOINT RESEARCH AND DEVELOPMENT BOARD 
PROGRAMS DIVISION (STR ERRATA) 

WASHINGTON 25, D. C. 

A master errata sheet will be compiled from these reports 
and sent to recipients of the volume. Your help will make 
this book more useful to other readers and will be of great 
value in preparing any revisions. 


SUMMARY TECHNICAL REPORT OF DIVISION 15, NDRC 


VOLUME I 


RADIO COUNTERMEASURES 


declassified 

By authority Secretary of 

SEP 30 1960 

Defense memo 2 August 1960 
LIBRARY OF CONGRESS 

OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT 
VANNEVAR BUSH, DIRECTOR 


NATIONAL DEFENSE RESEARCH COMMITTEE 
JAMES B. CONANT, CHAIRMAN 

DIVISION 15 

C. G. SUITS, CHIEF 


WASHINGTON, D. C., 1946 


NATIONAL DEFENSE RESEARCH COMMITTEE 

James B. Conant, Chairman 
Richard C. Tolman, Vice Chairman 
Roger Adams Army Representative^ 

Frank B. Jewett Navy Representative- 

Karl T. Compton Commissioner of Patents-^ 

Irvin Stewart, Executive Secretary 

^Navy 7'epresentatives in order of service : 

Rear Adm. H. G. Bowen Rear Adm. J. A. Furer 
Capt. Lybrand P. Smith Rear Adm. A. H. Van Keuren 
Commodore H. A. Schade 

^Conwiissioners of Patents in 07'der of service: 

Conway P. Coe Casper W. Corns 


'^Army representatives in order of service: 

Maj. Gen. G. V. Strong Col. L. A. Denson 

Maj. Gen. R. C. Moore Col. P. R. Faymonville 

Maj. Gen. C. C. Williams Brig. Gen. E. A. Regnier 

Brig. Gen. W. A. Wood, Jr. Col. M. M. Irvine 

Col. E. A. Routheau 


NOTES ON THE ORGANIZATION OF NDRC 


The duties of the National Defense Research Committee 
were (1) to recommend to the Director of OSRD suit- 
able projects and research programs on the instrumen- 
talities of warfare, together with contract facilities for 
carrying out these projects and programs, and (2) to 
administer the technical and scientific work of the con- 
tracts. More specifically, NDRC functioned by initiating 
research projects on requests from the Army or the 
Navy, or on requests from an allied government trans- 
mitted through the Liaison Office of OSRD, or on its 
own considered initiative as a result of the experience 
of its members. Proposals prepared by the Division, 
Panel, or Committee for research contracts for perform- 
ance of the work involved in such projects were first re- 
viewed by NDRC, and if approved, recommended to the 
Director of OSRD. Upon approval of a proposal by the 
Director, a contract permitting maximum flexibility of 
scientific effort was arranged. The business aspects of 
the contract, including such matters as materials, clear- 
ances, vouchers, patents, priorities, legal matters, and 
administration of patent matters were handled by the 
Executive Secretary of OSRD. 

Originally NDRC administered its work through five 
divisions, each headed by one of the NDRC members. 
These were: 

Division A — Armor and Ordnance 
Division B — Bombs, Fuels, Gases, & Chemical Problems 
Division C — Communication and Transportation 
Division D — Detection, Controls, and Instruments 
Division E — Patents and Inventions 


In a reorganization in the fall of 1942, twenty-three 
administrative divisions, panels, or committees were 
created, each with a chief selected on the basis of his 
outstanding work in the particular field. The NDRC 
members then became a reviewing and advisory group 
to the Director of OSRD. The final organization was 
as follows: 

Division 1 — Ballistic Research 

Division 2 — Effects of Impact and Explosion 

Division 3 — Rocket Ordnance 

Division 4 — Ordnance Accessories 

Division 5 — New Missiles 

Division 6 — Sub-Surface Warfare 

Division 7 — Fire Control 

Division 8 — Explosives 

Division 9 — Chemistry 

Division 10 — Absorbents and Aerosols 

Division 11 — Chemical Engineering 

Division 12 — Transportation 

Division 13 — Electrical Communication 

Division 14 — Radar 

Division 15 — Radio Coordination 

Division 16 — Optics and Camouflage 

Division 17 — Physics 

Division 18 — War Metallurgy 

Division 19 — Miscellaneous 

Applied Mathematics Panel 

Applied Psychology Panel 

Committee on Propagation 

Tropical Deterioration Administrative Committee 


iv 



JjECLASSTFTFn 
Ey authority Secretary of 


NDRC FOREWORD 


A S EVENTS of the years preceding 1940 re- 
^ vealed more and more clearly the serious- 
ness of the world situation, many scientists in 
this country came to realize the need of organ- 
izing scientific research for service in a national 
emergency. Recommendations which they made 
to the White House were given careful and 
sympathetic attention, and as a result the Na- 
tional Defense Research Committee [NDRC] 
was formed by Executive Order of the Presi- 
dent in the summer of 1940. The members of 
NDRC, appointed by the President, were in- 
structed to supplement the work of the Army 
and the Navy in the development of the instru- 
mentalities of war. A year later, upon the estab- 
lishment of the Office of Scientific Research and 
Development [OSRD], NDRC became one of 
its units. 

The Summary Technical Report of NDRC is 
a conscientious effort on the part of NDRC to 
summarize and evaluate its work and to pre- 
sent it in a useful and permanent form. It com- 
prises some seventy volumes broken into groups 
corresponding to the NDRC Divisions, Panels, 
and Committees. 

The Summary Technical Report of each Divi- 
sion, Panel, or Committee is an integral survey 
of the work of that group. The first volume of 
each group's report contains a summary of the 
report, stating the problems presented and the 
philosophy of attacking them, and summarizing 
the results of the research, development, and 
training activities undertaken. Some volumes 
may be “state of the art" treatises covering 
subjects to which various research groups have 
contributed information. Others may contain 
descriptions of devices developed in the labora- 
tories. A master index of all these divisional, 
panel, and committee reports which together 
constitute the Summary Technical Report of 
NDRC is contained in a separate volume, which 
also includes the index of a microfilm record of 
pertinent technical laboratory reports and ref- 
erence material. 

Some of the NDRC-sponsored researches 
which had been declassified by the end of 1945 
were of sufficient popular interest that it was 
found desirable to report them in the form of 
monographs, such as the series on radar by Divi- 
sion 14 and the monograph on sampling inspec- 
tion by the Applied Mathematics Panel. Since 


SEP 30 I960 

the material tr^ted in them is not duplicated 
in the Summar7^^^J19?h9l^(RBp!^xii^i^ 
the monographs ari i i r mortan t part of the 
story of these aspecfi^ ND^ 

In contrast to the information on radar, 
which is of widespread interest and much of 
which is released to the public, the research on 
subsurface warfare is largely classified and is 
of general interest to a more restricted group. 
As a consequence, the report of Division 6 is 
found almost entirely in its Summary Technical 
Report, which runs to over twenty volumes. 
The extent of the work of a division cannot 
therefore be judged solely by the number of 
volumes devoted to it in the Summary Technical 
Report of NDRC: account must be taken of the 
monographs and available reports published 
elsewhere. 

To the able men of Division 15, who worked 
under the direction of Dr. C. G. Suits, and to 
the personnel of the Division's contractors be- 
longs credit for the perfection of radio counter- 
measure devices and techniques which saved 
many American lives. Working in close coop- 
eration with the armed services, the Division 
carried out a program of research which led to 
the formulation of a fundamental doctrine of 
radio countermeasures. The RCM activities in- 
cluded the development and use of search-ether 
receiving equipment, jamming systems, con- 
fusion and deception devices, and antijamming 
techniques. RCM was used successfully in aerial 
operations covering the Normandy landings, 
and during the latter stages of the war RCM 
rendered German radar systems practically 
useless. 

The Summary Technical Report of the Divi- 
sion, prepared under the direction of the Divi- 
sion Chief and authorized by him for publica- 
tion, describes the Division's program and the 
devices and procedures which were developed. 
We join with a grateful Nation in expressing 
our sincere appreciation to the men of the Divi- 
sion whose work contributed so importantly to 
the victory. 

Vannevar Bush, Director 
Office of Scientific Research and Development 

J. B. CoNANT, Chairman 
National Defense Research Committee 







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FOREWORD 


T he summary technical report of Division 15 
is a compilation of technical contributions by 
the scientists and engineers of the contractors of 
Division 15, NDRC. The Division 15 wartime ac- 
tivity, called, for reasons of security, “Radio Co- 
ordination,” consisted of the development of elec- 
tronics countermeasures. Such countermeasures, for 
example, included the jamming and confusion tech- 
niques and equipments for use against radar and 
radio communications. Later in the war, counter- 
measures for newer types of electronics weapons, 
such as guided missiles, were developed. The whole 
field of activity included a great variety of radio and 
electronics specialties, unified in the common objec- 
tive of denying to the enemy the use of his elec- 
tronics equipments and weapons. 

Electronics countermeasures, generally referred 
to as RCM, started in World War II with the 
passage of the Gneisenau and Scharnhorst through 
the English Channel. This operation was screened 
from British radar by electronic jammers installed 
by the Germans along the Channel coast. The suc- 
cess of the operation stimulated the development of 
RCM in Britain and later in the United States. 

A small group was set up, under Dr. F. E. Ter- 
man, in the Radiation Laboratory at the Massa- 
chusetts Institute of Technology under Division D 
of NDRC, shortly after our entry into the war. This 
group later moved to Harvard University and be- 
came the nucleus of the Radio Research Labora- 
tory. Division 15 was formed about this time, with 
responsibility for the broad field of electronics coun- 
termeasures, and the whole effort grew to one of the 
large technical projects of the war. It was a fascinat- 
ing job and all the people associated with it felt they 
were contributing to victory. 

The excitement of the changing technical needs in 
the field contributed to the success of the work, and 
remarkable teamwork was achieved on a team 
whose signals were constantly being changed by the 
enemy. The countermeasures team depended greatly 
upon its members in the Army and Navy and Air 
Forces for the success of the civilian effort. 

Our allies, the British, made many important 
contributions to the success of RCM in World 
War II, particularly when the work was first getting 
under way in this country. Setting up the counter- 
measures group known as the American-British 
Laboratory Division 15, although intended prima- 


rily to serve the United States Eighth Air Force, 
did, to some slight extent, repay the British for 
their earlier help in this work. 

Division 15 had many contractors in universities 
and in industry, and their combined efforts com- 
prised the Division program. In the course of time, 
specialties developed, so that we gradually looked to 
Radio Research Laboratory, the largest of our 
laboratories, for the development of radar counter- 
measures; to the Airborne Instruments Laboratory, 
operated by Columbia University, for guided mis- 
siles countermeasures, and some additional still 
secret developments; industrial laboratories, par- 
ticularly those of the Bell Telephone Company, 
Radio Corporation of America and Federal Tele- 
phone and Radio Corporation, took the chief re- 
sponsibility for radio communications countermeas- 
ures; the special electronics tubes required for 
jamming purposes were developed in the labora- 
tories of the Westinghouse Electric Corporation, 
Federal Telephone and Radio Corporation, and 
General Electric; Ohio State University specialized 
in antenna measurements; and the firm of Jansky 
and Bailey studied the vulnerability of the United 
States radio to jamming by the enemy. 

One of the values that justifies a compilation of 
this kind is the technical lesson that may be learned 
for future guidance. One of the lessons of World 
War II is the necessity of giving some thought in 
time of peace to the problems of the national de- 
fense. It seems appropriate, therefore, at this point 
to draw attention to those technical problems which 
should be studied in the postwar period with future 
electronics countermeasures in mind. 

Although there are necessarily a great many 
detailed items in a wartime research and develop- 
ment program in the radio countermeasures field, it 
is believed that a continuing countermeasures pro- 
gram in peacetime, under the sponsorship of civilian 
and government agencies, should consist only of the 
four broad categories described below. 

It is probable that in the future, the ether will be 
filled with radio signals from a great many instru- 
ments of warfare such as radar, communications, 
guided missiles, proximity fuzes, and yet-to-be- 
developed controlled devices. The location, meas- 
urement, and analysis of these signals will be a vital 
activity in the future. It is believed, therefore, that 
a search ether program is one which must be a 


FOREWORD 


viii 


continuing activity beyond the war just ended. To 
this end a long-range continuing search project 
should be established. It has been urged by Divi- 
sion 15 that such a program be established by the 
Services. It is felt that this is the most important 
portion of the radio countermeasures activity and it 
should also be supported by a civilian research 
agency. 

Emphasis is placed on the research aspect of such 
an undertaking, since it is evident that new tech- 
niques must be developed and proved. The applica- 
tion of known conventional techniques would not be 
sufficiently effective to meet the need for searching 
the ether in another war; they were in fact only 
marginally adequate in the past war. The Radio 
Research Laboratory completed the development of 
an improved line of radar search receivers consistent 
with the OSRD philosophy concerning preservation 
of values, and the Airborne Instruments Laboratory 
completed what is considered to be a reasonably 
good search receiver for PF signals up to 275 me. 
These represent a rather high degree of perfection of 
presently known receiver design techniques. The 
program referred to in this volume is the perfection 
of systems of searching, requiring a pure research 
approach in order to develop new techniques which 
will really meet the needs. 

This art must be so developed that it will be pos- 
sible to monitor continuously the entire radio- 
frequency spectrum, providing a suitable visual dis- 
play showing any signals present as well as arrange- 
ments for recording such signals as may be received. 
The position of the signals in the spectrum should be 
accurately indicated, and means should be provided 
for identifying the character of any given signal 
(nature of modulation) and the direction from 
whence it is received. Provision should also be made 
for use of supplemental analyzer gear to determine 
in more detail the characteristics of the particular 
signal. There should be no spurious responses which 
could lead to false conclusions by the operator, 
neither should there be radiation from the receiver 
such as to interfere with other channels or to permit 
detection by an enemy. 

It is considered essential to future security that 
research and development on devices for generation 
of high-frequency energy, which could be used for 
electronics countermeasures purposes, go forward 
actively. Since one does not know where in the 
spectrum the various enemy signals will appear, it is 
necessary that there be developed and made avail- 


able sources of radio-frequency energy which, with 
suitable modulation, can be brought to bear on the 
enemy’s transmissions, wherever they may lie in the 
radio-frequency spectrum. 

It is believed that to a great extent commercial 
interests will provide the necessary impetus in this 
field, and that accordingly the postwar civilian re- 
search agency should adopt a countermeasures tube 
policy of carefully following commercial tube de- 
velopments in the light of potential RCM applica- 
tions. The trend of commercial developments may 
be expected to be toward higher frequencies and 
higher power levels, which would coincide with the 
RCM interest. There may, however, be gaps in the 
spectrum which will be left unfilled by commercial 
initiative alone, and it is suggested that the civilian 
research agency undertake to insure the filling of 
these gaps. It is hoped that this might be accom- 
plished by interesting a commercial organization in 
undertaking the work as a part of its own develop- 
ment program; in some instances, however, a 
sponsoring contract might be required. Also, the 
development of modulation techniques should be 
followed closely, to insure that RCM needs can be 
met. 

Another aspect of tube development that should 
be encouraged is that of broad tuning range. The 
restricted tuning range of magnetrons and velocity 
modulated tubes at the present state of the art 
entails vastly greater quantities of tubes and equip- 
ments for policing the spectrum than would be 
needed if really wide tuning ranges were available. 
If commercial interests do not vigorously promote 
research directed toward broader tuning ranges, it 
is believed that the civilian research agency should 
do so. 

The foregoing remarks relate principally to tubes 
for transmitting and receiving purposes. However, 
in relation to receiver type tubes it should be 
pointed out that tubes suitable for use in signal 
generators, broadly tunable and adequate in power 
output, likewise are needed and should be followed 
closely. 

It is believed that the development of non- 
reflecting surfaces will also have an important bear- 
ing upon any future armed conflict. It is expected 
that surface treatment of this sort will be essential 
not only in order to offset the usefulness of the 
enemy’s radar, but also to deny him the effective 
use of other weapons, such as proximity fuzes, whose 
operation depends upon the reflection of electro- 


FOREWORD 


IX 


magnetic waves. Emphasis should be placed on the 
broad band aspect of such surfaces, as the use of a 
great variety of frequencies by the enemy is a 
foregone conclusion. 

An important part of the RCM research and 
development program during World War II was the 
studying and evaluating of countermeasures tech- 
niques, in order to realize the greatest effectiveness 
from our countermeasures effort in combat. It is 
important that some continued studies of this sort 
go on during peacetime, taking into account the new 
electronic devices as they are developed, as well as 
any new means available for countering such de- 
vices. This would of course include consideration of 
spot or barrage jamming as well as various decep- 
tion devices, which would in turn be governed to 
some extent by the sources of jamming power avail- 
able, the refinement of broad band amplifier tech- 
niques, etc. It also should include full consideration 
of the use of non-reflecting surfaces as another 
means of nullifying the effectiveness of enemy 
weapons which depend upon the reflection of radio 
waves. 

Studies of the sort just mentioned should not be 
confused with the provision of an adequate counter- 
measure for any new device utilizing electromag- 
netic radiation. The importance of being able to 
counter any of our new electronic weapons which 
might be turned against us is well recognized, and it 
is believed that the Army and Navy laboratories are 


in the best position to provide such specific RCM 
devices for new weapons. It is hoped that the 
Services also will continue direct sponsorship of 
studies and evaluations mentioned above, but in 
any case it seems likely that the postwar civilian 
research agency will find it desirable to sponsor 
some continuing effort of this sort. 

It is never easy for scientists and engineers to 
write reports of their work long after the interesting 
technical job has been completed. This is particu- 
larly true in the preparation of reports of wartime 
jobs. In Division 15, for example, reports were pre- 
pared in many cases as laboratories were terminat- 
ing their work and as former employees were under- 
taking their postwar jobs. For these reasons great 
credit is due to the group of people who gave so 
generously of their time, in many cases long after 
their employment by NDRC or an NDRC con- 
tractor, to complete this vital record of one of 
America’s wartime technical accomplishments. 

Howard A. Chinn, as Editor-in-Chief, has per- 
formed a very great service in taking the responsi- 
bility for the technical content and arrangement of 
the material . He was ably assisted by those who are 
mentioned in the following Preface. The contribu- 
tions of this group, both in line of duty and beyond 
the line of duty, made possible the compilation of 
this work. 

C. G. Suits 
Chief, Division 15 



PREFACE 


T fie activities of NDRC Division 15 were prima- 
rily in the radio countermeasures field. In pre- 
senting the results of this work, this report is divided 
into four broad categories. These are (1) introduc- 
tion, (2) technical developments, (3) nonradar ap- 
plications, and (4) radar applications. 

The Introduction, which comprises the first 
chapter of this report, provides orientation in the 
relatively new field of radio countermeasures. Al- 
though radio was used in World War I (primarily 
for communication), no extensive countermeasures 
activities were practiced. In World War II, on the 
other hand, with radio techniques being used for an 
almost endless variety of applications, radio coun- 
termeasures assumed an exceedingly important and, 
in some cases, a decisive role. As with many of the 
other electronic applications, the success with which 
this new tool was employed was often a function of 
the ingenuity of the person responsible for its 
application. 

The fundamental technical developments which 
resulted from the work of Division 15 are described 
in five chapters, each covering a particular division 
of the work. A great many of the technical accom- 
plishments, although originally undertaken with a 
view to their application to radio countermeasures, 
are of considerable value and interest to the elec- 
tronics field in general. Because of the great diver- 
sity of requirements in the countermeasures field, 
there was an attendant development of a wide 
variety of techniques and equipment. These techni- 
cal developments will probably find greater postwar 
application than in the case of many other wartime 
electronic devices. 

The application of radio countermeasures tech- 
niques can be divided into (1) those for radar 
equipment and (2) all others. This division had no 
special significance. For convenience in nomen- 
clature the latter category is termed nonradar 
applications. 

In this report, the application of countermeasures 
to nonradar fields is covered in three chapters. A 
fourth, covering proximity fuze countermeasures 
has been omitted in view of the current security 
regulations. 


All told, six chapters are devoted to the applica- 
tion of countermeasures to radar systems. Four of 
these chapters deal with equipment developments, 
while two of them cover the use of countermeasures 
in the various theaters of operation of the Armed 
Forces. 

It is not possible within the scope of a report of 
this type to cover every development or to include 
all details of those developments that are men- 
tioned. For this reason, a bibliography of the tech- 
nical reports written by Division 15 laboratories is 
also presented. Of even more value is a digest of 
the contents of these reports. Report titles do not 
always convey an adequate description of the con- 
tents of the report. Therefore, the abstract of 
Division 15 Technical Reports, which is a part of 
this material, will prove very useful for deciding 
whether a given report contains material worthy of 
further review. 

The main burden of compiling the Division 15 
Summary Technical Report fell upon Roland B. 
Holt without whose able work the material could 
never have been adequately completed. James 
Wilson also assisted in compiling the material, and 
John N. Dyer acted as editor for Chapters 14 and 
15 covering radio countermeasures in the various 
theaters of operation. 

Frederick P. Cowan, David Middleton, Peter J. 
Sutro, and Donald W. Taylor contributed material 
contained in the Technique Development portion of 
this report. The last two chapters on applications in 
the theaters are a composite of information com- 
piled by Robert B. Barner, John S. Foster, Jr., 
Stanley F. Kaisel, James M. Moran, Joseph M. 
Petit, Eugene Fubini, Charles W. Oliphant, Robert 
D. Sard, Don R. Scheneck, and J. Gregg Stephenson. 

The abstract of technical reports issued by the 
Division was wholly the work of Arthur H. Halloran. 

This opportunity is taken to thank all those men- 
tioned above and also the many un-named assist- 
ants whose efforts contributed so much to the 
preparation of this report. 

Howard A. Chinn 
Editor-in-Chief 


XI 


r_* 


« ' 



CONTENTS 

CHAPTER PAGE 

Summary 1 

PART I 

INTRODUCTION 

1 Introduction to Radio Countermeasures 9 

PART II 

TECHNIQUE DEVELOPMENT 

2 Noise Sources and Transformers 19 

3 Electron Tube Development 39 

4 Antennas and Radio-Frequency Power Transmission 54 

5 Test Methods, Test Equipment, and Radio Countermeasures Training 66 

6 Theoretical Studies and Miscellaneous Developments 80 

PART III 

NONRADAR APPLICATIONS 

7 Nonradar Receiving and Direction-Finding Techniques and Equipment 149 

8 Nonradar Jamming Transmitter Techniques 160 

9 Nonradar Antijamming Techniques 188 

PART IV 

RADAR APPLICATIONS 

10 Receiving and Direction-Finding Equipment for Radar Counter- 
measures 203 

11 Radar Jamming Transmitters % . . . 214 

12 Radar Deception and Confusion 230 

13 Radar Antijamming Studies and Training 249 

14 RCM in the European and Mediterranean Theaters 264 

15 RCM in the Pacific Theaters of Operations 311 

Appendix 369 

Glossary 463 

Bibliography 467 

OSRD Appointees 497 

Contract Numbers 498 

Service Project Numbers 501 

Index 521 



. SUMMARY 


T he work of Division 15 in the field of radio 
countermeasures [RCM] had a very broad 
scope; it included fundamental research and 
development work on equipments for RCM, 
consultant services to manufacturers of these 
equipments, theoretical studies and other activ- 
ities which led to the formulation, in close co- 
operation with the Armed Services, of a funda- 
mental doctrine of the radio countermeasures 
science, and even included extensive participa- 
tion by its civilian scientists in the planning, 
execution, and analysis of countermeasures op- 
erations. 

The promulgation of the basic principles on 
which RCM operations were based, fortunately, 
was practically completed early in World War 
11. Briefly, RCM activities include the develop- 
ment and use of receiving equipment, jamming 
systems, confusion and deception devices, and 
antijamming [AJ] techniques. This broad di- 
vision of the field holds equally well for radar, 
communications, guided missiles, proximity 
fuzes, and other types of countermeasures. The 
problem generally repeats a familiar pattern: 
viz., the operating characteristics, location, and 
tactical use of the enemy equipment must be 
ascertained; the proper tactical and technical 
combination of jamming transmissions and/or 
confusion and deception techniques for render- 
ing this equipment as nearly useless as possible 
must be employed ; and finally, our own devices 
of a similar type must be protected against the 
enemy’s countermeasures activity. 

The extremely diverse nature of the frequency 
ranges, power output, type of signal employed, 
antenna directivity, and other features of 
enemy electronic equipment demands that a 
similarly diverse collection of RCM equipment 
be available. A complete countermeasures pro- 
gram, therefore, calls for the development of 
search receivers in all frequency ranges capable 
of handling all types of signals, transmitters of 
all power levels, frequency ranges, types of out- 
put signals, and other features, a very wide 
diversity of deception and confusion techniques 
and equipment, and as many AJ techniques as 
possible. Compromises have had to be made in 
the design of many RCM equipments, so that a 
given unit could be used in several ways, to 
prevent the necessity of developing an almost 


astronomical number of separate equipments. 
Since it was not feasible to manufacture in 
large quantities all the sets developed, it was 
necessary to make available, on the basis of 
probable need, large quantities of certain equip- 
ments, and to hold in reserve finished designs 
of other equipments for possible contingencies. 
For this reason, the Division 15 developmental 
program included the development of as many 
diverse equipments as time allowed; thousands 
of units of some types were manufactured, while 
some were never carried past the prototype 
stage. Although only a few of the developments 
described in this report received widespread 
operational application, the others were of in- 
estimable value as insurance. 

The radio countermeasures activities of Divi- 
sion 15 were roughly divided between radar and 
nonradar countermeasures activities. Certain 
developments and techniques were common to 
both fields ; these are discussed in the first main 
division of this report. Such activities include 
studies of modulation sources for RCM trans- 
mitters; electron tube developments; develop- 
ment of antennas and transmission lines; and 
development of test methods, equipment, and 
RCM training techniques. Many of the theoret- 
ical investigations carried on by the division 
were also applicable to both radar and nonradar 
countermeasures. 

It was recognized early in the RCM program 
that the most useful type of jamming signal 
was noise. Other specialized types of modulation 
were applicable in special cases, but well over 
90 per cent of the transmitters built for RCM 
use were noise-modulated. This meant that an 
extensive program for the investigation of noise 
sources and associated problems was necessary. 
Most of the work was centered on perfection 
of devices for the use of photoelectric and gase- 
ous-discharge noise phenomena, although cer- 
tain other miscellaneous types of noise produc- 
tion were investigated. In connection with the 
developments of the noise sources per se, it was 
necessary to build amplifiers which would cor- 
rect the faulty spectral distribution of the noise 
produced, and also to build transformers which 
would make the output of noise sources directly 
applicable to the modulation of transmitters. 
Such developmental work naturally included a 


I 


2 


SUMMARY 


considerable amount of fundamental research 
on the phenomena responsible for the produc- 
tion of noise, on the modification of these phe- 
nomena by imposed conditions (such as mag- 
netic fields) , on the development of methods for 
measuring noise, and on the fundamental elec- 
trical properties and materials used in the con- 
struction of noise-handling transformers. 

The RCM program required the development 
of a large variety of vacuum tubes. This is eas- 
ily understood in view of the fact that it was 
necessary to cover, at various power levels, 
large portions of the spectrum which were vir- 
tually unexplored at the beginning of World 
War II. It was necessary that this coverage be 
made by tubes having suitable ease of tuning, 
modulation properties, and operating stability. 
The electron tube developmental program spon- 
sored by Division 15 resulted not only in the 
production of several dozen types of tubes, but 
also contributed in a fundamental way to the 
basic theory of tube design and to several re- 
lated fields of endeavor. Tubes suitable for local 
oscillator applications in the frequency range 
3,000 to 11,500 me were reduced to practice. 
Parallel-plane triodes, suitable for use as am- 
plifiers and oscillators for frequencies as high 
as 3,000 me, were developed. A series of low- 
and medium-power magnetrons, including split- 
anode and “squirrel-cage’^ types, were developed 
in the frequency ranges from about 90 me to 
well over 3,000 me. Higher-power magnetrons 
for use in the high-frequency range were devel- 
oped which were capable of delivering as much 
as 10-kw output. A new type of tube, the resna- 
tron, was developed which was capable of power 
outputs of the order of 50 kw at 500 me. Many 
of these tube developments will undoubtedly 
have a profound effect upon future electronic 
research and development, especially in view of 
the fact that the tube program represented an 
effort to cover as much of the frequency spec- 
trum as was feasible, at all power levels, 
with tubes capable of being tuned over large 
ranges. 

A further extremely important consequence 
of the tube development program was the care- 
ful study, much of it in the nature of basic re- 
search, of the fundamental principles of oper- 
ation of some of the tubes produced. The work 


with magnetrons, velocity-modulated tubes, and 
resnatrons is especially noteworthy in this con- 
nection. In a similar way, research done on 
coaxial and open-wire line oscillator circuits 
and resonant cavity circuits for use with these 
tubes is of great importance in the field of basic 
electronics. 

The antenna and r-f power transmission re- 
search and development carried on by Division 
15 was necessary because antennas suitable for 
RCM applications having the required fre- 
quency range, directivity patterns, and physical 
configurations, were not available. The most 
remarkable single feature of the antennas de- 
veloped in this program was the extended band 
coverage. Receiving antennas operating over 
frequency ranges of 3 to 1 were not uncommon, 
and transmitting antennas with very large 
bandwidths were developed. Although attention 
was given to antennas for ground-based, ship- 
borne, and airborne use, the very nature of the 
countermeasures program dictated a wider use 
of airborne equipment than of any other types. 
Consequently, more attention was given to air- 
borne antennas than to other kinds. 

Dozens of antenna types were investigated, 
and a great number of these reached the pro- 
duction stage. As was the case with other RCM 
equipment, the number of antennas of a given 
type which were used, operationally depended 
very widely. Over 10,000 of one type of antenna 
described in this report were manufactured, 
and only 1 or 2 of several other types were used 
in actual operations. Here, again, the techniques 
developed, especially along the line of wide fre- 
quency coverage antennas for aircraft, are 
likely to prove of considerable value for future 
applications. 

Among the features of some of the counter- 
measures antenna developed are their wide fre- 
quency coverage, their considerable variety in 
directional patterns, their polarization charac- 
teristics (including some which were circularly 
polarized), and their various mechanical fea- 
tures (such as low drag type antennas for high- 
speed aircraft). The frequency range covered 
in Division 15 investigations was from the 
broadcast range up to well above 10,000 me. 
As mentioned above, it was necessary to employ 
several entirely new types of antennas to real- 


SUMMARY 


3 


ize the objectives of the program. Radio-fre- 
quency power transmission equipment, such as 
r-f switches, special transmission lines, and 
filters were also found to be necessary adjuncts 
to the RCM program and were therefore in- 
cluded as a part of the developmental effort. 

Testing techniques, both for laboratory use 
and for field use, were found to be of the utmost 
importance in the radio countermeasures pro- 
gram. The extremely diverse nature of the RCM 
equipment developed demanded an even more 
diverse line of test equipment. This included 
special tube testers, noise analyzers, watt- 
meters, wavemeters, transmitter alignment in- 
dicators, heterodyne frequency meters, test os- 
cillators, signal generators, crystal voltmeters, 
wide-band oscilloscopes, antenna measuring 
equipment, spectrum analyzers, equipment for 
receiver vulnerability testing, and many other 
types of specialized test equipment. Many of 
the devices employed for laboratory testing 
were packaged in a form suitable for field ap- 
plication, and moderate numbers were manu- 
factured. Here, again, many of the techniques 
employed were of a fundamental nature and 
will influence electronic research and develop- 
ment for some time to come. Many of the meth- 
ods and some of the equipment growing out of 
this program were found to be directly applica- 
ble to the training of Service personnel respon- 
sible for the operation and maintenance of test 
equipment. 

The theoretical work done by Division 15 in- 
cluded basic studies on jamming signals, studies 
on the transmission and reflection of energy, 
and various miscellaneous investigations. The 
studies of jamming signals included basic noise 
studies, theoretical and basic experimental work 
on the visibility of radar signals through noise, 
and frequency-modulation investigations. These 
studies had a profound influence upon the de- 
sign requirements finally adopted for the band- 
width, type of modulation, power output, etc., 
of jamming transmitters, and also on the AJ 
recommendations it became possible to make 
for the design of better radar, communications, 
and other electronic equipment. 

The investigation of the transmission and 
reflection of energy had direct application to 
the design of transmission lines, wave guides, 


and antennas. It also had considerable influence 
on the development of confusion and deception 
electromagnetic wave reflectors (see below). 

Miscellaneous topics investigated included 
theoretical studies of the method of operation 
of magnetrons, calculations of the probability 
of intercepting enemy signals of an intermit- 
tent character with a search receiver, an inves- 
tigation of the use of models in design of an- 
tennas and in studying radar echoes, and vari- 
ous other topics. Although no essentially new 
mathematical techniques were employed, the 
solution of some of the problems required rather 
novel methods of attack, and the guiding influ- 
ence on the overall RCM program of the the- 
oretical work done cannot be overemphasized. 

The nonradar applications of countermeas- 
ures equipment are discussed in the second 
main division of this report. These applications 
included development of receiving and direc- 
tion-finding [DF] techniques and equipment, 
jamming transmitter techniques and equipment, 
AJ techniques, and special techniques for prox- 
imity fuze countermeasures. 

It was found that, for most communications 
intercept work, commercially available receiv- 
ers were adequate. Some work on the arrange- 
ment of a combination of such units in a suit- 
able way (especially on aircraft) was found 
necessary to provide a complete search and 
monitoring service. The noncommunications 
portion of this activity, however, required spe- 
cial equipment. 

A considerable amount of work was done on 
countermeasures and anti-countermeasures for 
radio-navigation aids, on the development of 
radio direction finders and their countermeas- 
ures for the frequency range 1.5 to 100 me, on 
methods for deception of enemy DF equipment, 
and on electronic tuning for panoramic recep- 
tion. Many of the techniques investigated are 
of permanent value. Specific equipment devel- 
opments in this field included a panoramic re- 
ceiver for guided missile and other intermittent 
signal search, and a special recording receiver 
designed to be incorporated in a signal-repeat- 
ing jamming system. 

Application of jamming transmitters to the 
nonradar countermeasures problem involved a 
considerable amount of preliminary study. For 


4 


SUMMARY 


example, in jamming guided missiles and similar 
devices, noise is not always the most advanta- 
geous type of modulation ; consequently, a study 
of the effectiveness of various types of jamming 
signals had to be undertaken. Here, too, the 
relative advantages of barrage jamming (jam- 
ming over a wide frequency range) versus spot 
jamming (jamming only the victim-signal fre- 
quency) had to be weighed carefully before de- 
signing equipment to do a particular jamming 
job. Actual equipments developed for this type 
of application included airborne, parachute- 
borne, ship-borne, and ground-based units with 
power outputs varying from a few watts to 
several kilowatts. 

A considerable number of our own electronic 
devices were studied in order that specific sug- 
gestions could be made as to design of equip- 
ment or modifications for existing equipment 
to minimize the effects of enemy jamming. A 
necessary preliminary to this investigation, of 
course, was a study of the fundamental prop- 
erties of various types of jamming and of the 
vulnerability of various types of electronic 
equipment to jamming. Special test equipment 
was developed for some of these studies. A large 
number of communications systems, including 
voice, radiotelegraph, radioteleprinter, pulse 
communication systems, etc., were studied and 
definite recommendations as to improvement 
made. Several types of guided missile receivers, 
radio altimeters, and other similar devices were 
also studied. 

Because of the special nature of the problems 
involved and the high degree of security neces- 
sary, the work done on proximity fuzes was a 
more or less separate part of the RCM program. 
General studies were made, both theoretically 
and experimentally, of proximity fuzes and of 
possible countermeasures to them. The meas- 
ures considered included the use of confusion 
reflectors (Window) as well as of electronic 
jamming. Various types of jamming modula- 
tion were considered, and two jamming trans- 
mitters were developed to the production stage 
during World War II, as insurance in case the 
need for them arose suddenlv. A special search 
receiver for detecting proximity fuze signals 
was also developed. Since the enemy employed 
no proximity fuzes during the war, proximity 


fuze countermeasures operations were limited 
to search activities. 

The third principal section of the report is 
devoted to applications to radar countermeas- 
ures, which, because of the tactical situation, 
proved to be the most useful part of the pro- 
gram in World War II. Here, again, the pro- 
gram involved development of receiving and 
direction-finding techniques and equipment, 
jamming transmitters and systems, deception 
and confusion techniques, and antijamming 
methods. 

Receiving equipment developed for counter- 
measures use included a complete line of search 
receivers in the frequency range 40 to 11,500 
me. The development of such receivers made 
necessary a considerable amount of work on 
the fundamental properties of r-f filters, mixers, 
local oscillators, amplifiers, presentation cir- 
cuits, and other fundamental circuits required 
by these receivers. Many of the techniques de- 
veloped as the result of these studies should 
prove useful for a long time to come in wide- 
band receiver design. 

In addition to such search and analysis re- 
ceiving equipment, receivers for warning that 
a target was being observed by enemy radar, 
receivers for setting jamming transmitters on 
enemy radar frequencies, and receivers employ- 
ing other special design features (such as very 
rapid sweep, etc.) were also designed. The 
Armed Services procured several thousand re- 
ceivers based on fundamental Division 15 de- 
signs. 

Radar jamming transmitter developments in- 
cluded a wide variety of equipments, with power 
outputs from a few watts to many kilowatts, 
frequency coverages from about 20 me to sev- 
eral thousand me, and a considerable range of 
other features. These transmitters ranged in 
size from the small low-power transmitters 
which, before the end of World War II, flew in 
every heavy bomber in the European Theater 
of Operations [ETO] to the giant ship-borne 
Elephant jamming system and the ground-based 
Tuba jammer, both of which were able to put 
out tons of kilowatts of power. 

The jammers varied widely in complexity: a 
simple barrage jammer which was adjusted 
before an operation and merely turned on and 


SUMMARY 


5 


off as occasion demanded; a completely auto- 
matically operating jamming system capable of 
searching out and jamming enemy transmis- 
sions by itself; a jamming system employing 
several operators at once and capable of deter- 
mining the frequency, pulse length, pulse-repe- 
tition frequency, direction, frequency stability, 
and many other features of an enemy signal. 
Here, as in many other parts of the Division’s 
work, the techniques perfected during the de- 
velopment of specific equipments are of funda- 
mental and lasting value. 

Closely related to the use of jamming trans- 
mitters is the use of radar deception and con- 
fusion devices. The more widely used devices 
in this category have been mechanical reflec- 
tors, although electronic deception and confu- 
sion devices are also available. The mechanical 
reflectors are, essentially, metal foil cut in vari- 
ous sizes and shapes. They include narrow strips 
a half wavelength long, very long strips, corner 
reflectors, and many other miscellaneous types. 
Many tons of such metal foil deception and con- 
fusion devices were employed during World 
War II. 

A great deal of theoretical and experimental 
work was done to determine the optimum size 
and shape for such reflectors. It was also neces- 
sary to conduct many experiments and a con- 
siderable amount of theoretical investigation to 
determine the optimum tactics of the use of 
such reflectors. The combined use of this coun- 
termeasure and electronic jamming, which was 
carried out on a large scale in the ETO, ren- 
dered the enemy’s radar system practically use- 
less during the closing phases of World War II. 
In addition to the mechanical deception and 
confusion devices, various electronic means of 
disguising either the direction, range, or ap- 
parent size of a radar target are available and 
have been used operationally with success. 

Protection of our own radar sets against 
jamming activity of the enemy was also a part 
of Division 15 activity. A number of laboratory 
studies concerned with the development and 
application of good basic AJ design for radars 


were carried out. Investigations were made of 
many specific radar equipments, and the engi- 
neering of retroactive AJ modifications for 
radars already in the field was carried through 
for several systems. 

Radar AJ, more than almost any other part 
of the countermeasures program, depends for 
its effectiveness upon operator training. Conse- 
quently, a part of the program of the division 
was devoted to the development of training ap- 
paratus and the training of instructors in AJ 
techniques for the Armed Services. 

The participation of the division in opera- 
tional phases of World War II furnished a great 
deal of information which was of value to the 
division in the design of RCM equipment. At 
the same time, it aided the Armed Services by 
providing RCM equipment experts in the field. 
Division 15 personnel participated as early in 
World War II as the first operations in the 
Aleutians and in the invasion of Sicily. 

A branch laboratory with a staff of about 
80 people was maintained for over a year in 
England by Division 15. There were also Divi- 
sion 15 representatives in the Mediterranean 
Theater, in France immediately after the inva- 
sion, and in the investigating groups that went 
into Germany after the surrender. Division 15 
representatives also, at one time or another, 
visited every important center of countermeas- 
ures activity in the Pacific Theater. The effec- 
tiveness of such civilian aid was enhanced by a 
system of rotation, whereby men with the latest 
laboratory techniques were frequently sent to 
replace those with theater experience, who in 
turn helped formulate the future research policy 
of the Division. 

Analysis of the results obtained from the 
operational use by the Armed Services of RCM 
equipment leaves no doubt as to the soundness 
of the “investment.” The entire cost of the pro- 
gram was paid for over and over again by the 
saving in aircraft alone (not to mention the 
number of priceless lives also saved) result- 
ing from successful application of the equip- 
ment and techniques developed by Division 15. 





PART I 


INTRODUCTION 



x»** 


Chapter 1 

INTRODUCTION TO RADIO COUNTERMEASURES 


INTRODUCTION 

T he neutralization of the effectiveness of 
enemy radio communication, radar, and 
controlled-device systems by electronic or other 
means is known as radio countermeasures 
[RCM] . RCM also includes the problem of radio 
intercept [RI] but, since this is predominantly a 
tactical problem, it is not treated in this book, 
which is concerned mainly with technical mat- 
ters. 

Application of RCM requires careful prep- 
aration. The degree of success will usually de- 
pend upon the craftiness of those planning the 
operation, the speed of its application, and the 
skill of its execution. The importance of plan- 
ning, speed, and execution becomes obvious 
when it is remembered that the enemy is “call- 
ing the tune.’^ Whether communications, radar, 
or radio-controlled devices are used, the enemy 
selects the frequencies, the output power, the 
location and amount of the equipment, and the 
operating procedures. The effectiveness of the 
enemy’s activities will therefore depend upon 
our nimbleness in making use of available 
means to nullify these activities. By the same 
token, the enemy’s continued success depends 
upon the speed with which he can shift fre- 
quencies, locations, etc., and start the cycle 
over again. The application of RCM can thus be 
described as a continual scramble or series of 
“emergencies.” 

Since it was not feasible in World War II to 
equip every theater with jamming transmitters 
and other countermeasures devices for use 
against every possible type of radio equipment, 
those on the spot had to make effective use of 
equipment on hand whenever the enemy turned 
up at unexpected places in the frequency spec- 
trum. As this point cannot be overemphasized, 
an attempt has been made here not only to in- 
clude a description of the actual equipments 
which have been used for RCM purposes and of 
the actual techniques employed but also to set 
forth some of the fundamental philosophy that 
is essential to the successful use of these de- 
vices. 


1.2 types of countermeasures 

Basically, the methods employed for com- 
munications, radar, and controlled-devices coun- 
termeasures include straightforward jamming 
and the use of deception and confusion devices. 
Jamming may be considered a “brute force” 
method of accomplishing the desired result, 
whereas confusion and deception devices may 
be thought of as a more subtle method of at- 
tack. 

Closely allied to these direct RCM methods is 
the use of homing and direction-finding [DF] 
receivers and, in the case of radar, of warning 
devices to advise when one is being scrutinized 
by enemy radar systems. Furthermore, in both 
communications and radar, various antijamming 
[AJ] techniques may be applied. Finally, since 
the successful application of RCM implies an 
accurate knowledge of the disposition, operating 
characteristics, and habits of the enemy sys- 
tems, it is essential that adequate search equip- 
ment also be available as part of the complete 
RCM program. Search equipment, or suitable 
modifications of search equipment, must also 
often be used for monitoring the enemy trans- 
missions during the application of direct RCM 
procedures. Thus, RCM facilities include 

1. Receivers (search, monitoring, warning, 
and homing or direction-finding types). 

2. Jamming transmitters. 

3. Confusion and deception devices. 

4. Antijamming techniques. 

Since the method of practicing RCM in the 
communications field is often different from 
that which is appropriate in the radar field (or 
in allied applications, such as radio-controlled 
devices), it is important to differentiate be- 
tween the two fields. This is done in the follow- 
ing discussion and it is essential that this 
definite distinction always be kept in mind. 

Receivers 

Search Receivers 

Before the use of jamming transmitters or 
confusion and deception devices can be planned 


9 


10 


INTRODUCTION TO RADIO COUNTERMEASURES 


in detail, accurate information must be avail- 
able concerning enemy communications, radar 
equipment, and radio-control systems. In the 
preliminary stages of the planning it may be 
sufficient to make use of such generalized infor- 
mation as may be available concerning the 
probable numbers of enemy equipments, their 
disposition, and the frequency band in which 
they operate. For a specific application, how- 
ever, it is essential to know the exact fre- 
quencies employed by the systems to be neu- 
tralized, their methods of operation, what 
reserve facilities are available to the enemy, and 
the geographical locations of the systems in- 
volved. Such details are required because, in 
general, the jamming or deceptive means to be 
used must be accurately adjusted for the fre- 
quencies involved and operated only when they 
are likely to be effective and in such a manner 
as to neutralize all enemy facilities (or at least 
as many as possible) , whether they are regular 
or emergency systems. 

The equipment used for searching, analyzing, 
and direction-finding on enemy communications 
channels is, for the most part, conventional in 
design and has been catalogued elsewhere.^ For 
this reason, the only communications search 
equipment covered in this book is that which 
was developed for special purposes by the labo- 
ratories operating under the auspices of NDRC 
Division 15. Equipment operating at radar fre- 
quencies, however, is relatively new and is 
therefore covered in detail. 

A properly equipped searching expedition, in 
addition to being used to determine the radio 
frequencies employed, can ascertain many other 
operating characteristics of the enemy equip- 
ment. A knowledge of these characteristics will 
not only considerably facilitate neutralization 
of the equipment but will also provide informa- 
tion that may be valuable from an intelligence 
standpoint. In lieu of the actual capture of an 
enemy system, such data permit an informed 
estimate to be made of the capabilities of the 
equipment. 

Radar search can generally be most readily 
accomplished by observations made from air- 

a See the Signal Communication Equipment Directory 
prepared by Military Intelligence Branch, Office of the 
Chief Signal Officer. 


craft, since the emissions from such systems 
seldom extend appreciably beyond the radio 
“line of sight.^’ Thus, unless the terrain is par- 
ticularly favorable, only those radar equipments 
which are immediately adjacent to the fighting 
front will be observable by ground-based radar 
search receivers. This was true in the European 
Theater of Operations [ETO] between the Brit- 
ish Isles and the Continent. In the Alaskan 
Theater, the terrain was such that observations 
of the enemy radar equipment on Kiska could 
be made from Amchitka. Thus, although air- 
borne searching may be more common, the de- 
sirability of being prepared to undertake such 
operations with mobile, portable, or ground- 
based equipment must be borne in mind. The 
search receivers described herein are primarily 
intended for airborne applications but can be 
adapted to these other types of service. 

In connection with airborne search, it should 
be noted that radar emissions can be received 
at distances from the radar that are consider- 
ably beyond the maximum detection range of 
the radar system. Under these circumstances it 
is often possible to observe the operating char- 
acteristics of an enemy radar system without 
coming within its field of view. 

Receivers for determining the characteristics 
of the control signals used for enemy radio- 
controlled devices (e.g., radio-controlled tanks, 
glide bombs, or rockets) present a particularly 
difficult search problem. This arises from the 
fact that the signals are observable only for the 
few seconds (perhaps a minute, at the very 
most) in an actual attack during which the 
vehicle is making the target run. Even within 
this short period of time the control signals may 
not be continuously radiated, since they may 
of necessity be intermittent. Furthermore, the 
control signals may be confined to a very narrow 
channel, located almost anywhere in the radio 
spectrum. Finally, false or decoy signals, on 
frequencies far removed from those actually 
used, may be transmitted by the enemy during 
the attack. 

Monitoring Receivers 

Receivers for monitoring enemy transmis- 
sions or for “setting on’^ jamming transmitters 
are essential to many RCM operations. In the 


TYPES OF COUNTERMEASURES 


11 


first place, such equipment allows monitoring 
of the enemy transmission. This can provide a 
great deal of very useful information, especially 
if the enemy indicates the effectiveness of the 
RCM operation being attempted against him by 
attempting to change frequency, shutting off 
his equipment, turning off lobe switching (on 
radars), or otherwise changing his mode of op- 
eration. In the second place, use of such equip- 
ment for setting on a jammer will obviate the 
necessity for absolute determination of fre- 
quency, since the equipment can be arranged 
to receive both the signal and the jamming 
simultaneously and will allow following with 
the jamming transmitter any frequency shifts 
which the enemy may attempt to avoid the 
jamming. 

Direction-Finding and Homing Receivers 

Direction-finding means are also a part of the 
search program, since it is essential to ascertain 
the location of enemy installations. Because of 
the wide frequency range that is of interest, the 
various polarizations of the signal, and other 
factors, this is not a simple problem. Successful 
systems have been devised, nevertheless, and 
are described elsewhere in this volume. 

Homing receivers are another important type 
of RCM equipment, since they may be instru- 
mental in making it possible to undertake a 
most effective counter-countermeasure — find- 
ing and destroying enemy jammers. Besides 
being useful for homing on the source of enemy 
jamming transmissions, such receivers can also 
be used to home on friendly or enemy communi- 
cations and radar systems. 

Warning Receivers 

Radar warning receivers, which are more or 
less automatic in operation, are useful for ad- 
vising when one comes under observation by 
enemy radar. For example, an aircraft-intercep- 
tion [AI] warning system may be used to warn 
aircraft when attack by radar-equipped enemy 
fighters is imminent. A gun-laying [GL] , search- 
light-control [SLC], or ground- controlled-inter- 
ception [GCI] warning receiver would advise 
when danger from these sources is likely. Ex- 
perience has shown that the protection afforded 
by equipment of this kind is valuable for easing 


the inevitable tenseness that accompanies the 
possibility of attack without warning. 

In addition to its application to aircraft, such 
equipment is also useful, of course, for warning 
surface vessels or submarines of exposure to 
various types of radar. The use of warning 
receivers requires, however, a thoroughly ac- 
curate and reliable tabulation of the character- 
istics and methods of use of the enemy installa- 
tions. 


^ ^ ^ Jamming Transmitters 

Jamming transmitters are usually designed 
for use against a specific type (or types) of 
enemy system. They may be classified as air- 
borne, portable, mobile, expendable, ship-borne, 
or ground-based, depending upon their intended 
method of use. Because of wave propagation 
considerations, a given short-distance communi- 
cations or radar channel can, in general, be 
jammed with the minimum of power if the 
jammer is airborne. Airborne jammers are, 
however, faced with many limitations, such as 
limited primary power supply, problems of an- 
tenna installation (particularly at the lower 
communication frequencies) , difficulty of main- 
taining a continuous jamming operation, de- 
pendence upon weather, and vulnerability to 
attack. For these reasons, the use of ground- 
based, mobile, or portable jamming equipment 
is indicated wherever practical. 

The most important advantages of ground- 
based jamming transmitters are the relative 
ease of continuous operation (if required), the 
possibility of inconspicuous location, and the 
availability of greater amounts of primary 
power. Advantage may also be taken of avail- 
able space to employ directive-antenna systems 
in order to send a large percentage of the 
available power toward the victim and away 
from any friendly systems that may be operat- 
ing in the same general region of the frequency 
spectrum. Unfortunately, however, the dis- 
tances involved, the nature of the surrounding 
terrain, and the amount of transmitter power 
that can be conveniently radiated do not permit 
the widespread practice of jamming from 


12 


INTRODUCTION TO RADIO COUNTERMEASURES 


ground locations, particularly in the case of 
radar. 

Expendable jammers are generally of the 
type that may be dropped close to the victim 
station by parachute or in a bomb casing. A 
desirable feature of this type of jammer is that 
it may be sowed in quantities near the victim, 
where it will operate until located and destroyed 
or until the power supply is depleted. Such 
jammers can be effective even though they have 
very low power. Expendable transmitters seem 
to offer more possibilities in the communica- 
tions field than in radar, and, consequently, 
their development in the latter field has not 
been exploited to any extent. 

Communications Jamming 

Communications jamming transmitters, if 
properly used, can be very effective against 
ground force command nets, armored vehicle 
communication systems, walkie-talkie equip- 
ments, air-to-air and air-to-ground communica- 
tions systems, and other relatively short-dis- 
tance communications channels. Although it is 
possible, under favorable conditions, to attempt 
to jam long-distance point-to-point circuits, the 
success of such operations may be rendered 
unprofitable by the amount of power that may 
be needed, by the lack of suitable geographical 
locations for the jammer (which must blanket 
the terminal of the enemy channel with a fre- 
quency determined by the intended victim) , by 
the large number of frequency channels that 
the enemy may have available for emergency 
use, and by the need for jamming all channels 
practically continuously if the ‘‘blockade"’ is to 
be effective. 

In any event, the jamming of communications 
circuits of any kind must be coordinated with 
the activities of any intelligence services that 
may be using the channels to obtain information 
concerning enemy activities. The benefits to be 
gained by jamming must always be weighed 
against those to be obtained by monitoring the 
intended victim signal for information purposes. 

Jamming of enemy ground-to-air communica- 
tions channels may be a very effective means of 
neutralizing the effectiveness of enemy GCI 
radar systems. In fact, it is just as effective 
as jamming the radar itself since, if proper in- 


structions cannot be transmitted to the inter- 
ception fighter, the usefulness of the GCI system 
is destroyed. The jamming of such ground-to- 
air circuits may be most readily accomplished 
by airborne jammers in the vicinity of the vic- 
tim stations. Where an alternative exists, how- 
ever, this may not be the best method, since 
such airborne jammers may become the target 
of enemy action. 

In favorable situations, high-powered, ground- 
based communications jamming equipment, 
using directive antennas, may be advanta- 
geously employed to send signals into the region 
where enemy GCI fighters are operating. This 
procedure will result in the jamming of only 
the ground-to-air link (and not the air-to- 
ground link) . Since the ground-to-air link is the 
important link of the GCI system, however, its 
jamming should make GCI operations impos- 
sible or at least very difficult. 

Aircraft-Interception Radar Jamming 

If the enemy fighters are equipped with AI 
radar, it will be desirable to jam the AI system 
also. Again, this can be done most effectively 
with airborne jammers but they, in turn, may 
become the object of an attack guided by 
homing devices. In this case, also, if the distance 
and the terrain involved are favorable, use may 
be made of high-powered, ground-based jam- 
ming transmitters operating at the enemy AI 
frequencies. 

Gun-Laying and Searchlight-Control 
Radar Jamming 

In the jamming of GL and SLC radar (also of 
GCI radar, if the radar itself is to be jammed) , 
the jamming equipment must be airborne, gen- 
erally by the target aircraft, since the resolu- 
tion of these radar equipments will probably be 
such as to discriminate reasonably well against 
interference from directions other than that in 
which the radars are oriented. In daytime tight- 
formation flying, all jammers coming within 
the beamwidth of the radar will contribute to 
the overall effect but, at the same time, all tar- 
gets within a pulse length will contribute to the 
size of the radar echo.^ 

^ For further explanation see discussion of opera- 
tional tactics in Chapter 11. 


TYPES OF COUNTERMEASURES 


13 


Early-Warning Radar Jamming 

Early-warning [EW] radar systems may be 
effectively jammed by airborne equipment or by 
ground-based transmitters where the geograph- 
ical features of the situation are favorable. It is 
important to note that jamming operations 
must be carried out against all existing systems, 
regardless of their frequency, if the overall op- 
eration is to be successful. It has been found 
that in some theaters of operations, for ex- 
ample, the ETC, the need for EW jamming had 
to be carefully evaluated in view of the prox- 
imity of the fronts and the large concentration 
of other types of radar which, in such special 
situations, made possible the supplying of all 
the warning that is of practical value. Where 
EW radar is used to place GCI radar on the 
target, the jamming of the former (as well as 
of the latter) may be of some value. 

In any radar jamming operation it is im- 
portant not to use the jamming transmitter 
before entering the field of view of the intended 
victim radar. If the jammer is used too soon, 
the jammer-carrying craft will advertise its 
presence to the enemy by indicating the bearing 
(but not the range) from which the jammer is 
approaching. 

Coastal-Watch Radar Jamming 

Coastal-watch radar may be jammed from 
transmitters carried on shipboard or on low- 
flying aircraft or, when a suitable location is 
available, from ground-based jammers. As with 
all radar jamming, it is important to note that 
the radar will be subject to jamming only when 
it is pointed toward the source of jamming sig- 
nals. The resolution of the radar receiving an- 
tenna determines the arc over which it is 
susceptible to interference. If jamming over a 
considerable arc is desired, it will be necessary 
to employ a number of jamming sites. 

Radio-Controlled Devices and 
Proximity Fuze Jamming 

For the most part, jamming (or other RCM 
operations) attempted against radio-controlled 
devices or proximity fuzes is highly specialized 
and depends very largely upon the characteris- 
tics of the equipment which is being countered. 
Transmitters, receivers, etc., developed for 


other purposes may be used in this work in 
many cases. Very little of a general nature may 
be said. Specific equipments and techniques for 
radio-controlled devices RCM are, however, dis- 
cussed in Chapters 7 and 8, and specific equip- 
ments for proximity fuze RCM, in Chapter 10. 


Confusion and Deception Devices 

Communications Confusion and 
Deception Methods 

The application of confusion and deception 
methods in communications channels does not, 
for the most part, require any special devices 
other than transmitting and receiving equip- 
ment operating on the proper frequencies. Such 
practices do require ingenuity on the part of the 
operator. 

Radar Confusion Methods 

The method which has been most used for 
confusing enemy radar is the '‘Window opera- 
tion.” A Window operation involves the sowing 
of radar echo-producing reflectors to the extent 
that an entire volume of space becomes infested 
and the multiplicity of echoes of false targets 
will conceal a true target in this volume. 

The appearance of these false echoes is not 
very different from that of an aircraft except 
that their apparent speed, which depends upon 
the wind velocity, is very low. For complete 
protection the infestation must be sufficiently 
dense that the false echoes are strong enough 
to conceal the echo from an aircraft flying 
through the infested volume. Reflectors sown 
from the surface by means of rockets or sus- 
pended from a balloon or kite to simulate a 
surface target have been used, especially for 
naval applications. 

Radar Deception Methods 

Considerable attention was paid in the RCM 
program to methods of deceiving radar opera- 
tors. The objective was to cause the enemy 
operator to make a false report, not knowing 
that the echo received by his equipment was 
not that of a legitimate target. A Window op- 
eration may be so carried out as to fall into this 
category, particularly in areas where Window 


14 


INTRODUCTION TO RADIO COUNTERMEASURES 


has been in regular use and the enemy radar 
operator is used to seeing it as cover for a 
normal raid. A few aircraft carrying sufficient 
Window may eject it at a high rate in a rendez- 
vous area, if in view of enemy EW radar, in 
order to alert the enemy’s defense system on 
days when no raid is planned. Another scheme, 
where there are several possible targets in one 
area, is to send a few special aircraft with suf- 
ficient Window as a diversionary raid. Then, if 
Window is dropped in the proper quantity by 
the main raid, there will be no way for the 
enemy radar operator to distinguish between 
the main raid and the diversion. Obviously, in 
using Window to deceive EW radars, the fre- 
quency coverage must include all radars which 
the enemy will use for this purpose. 

Various electronic deception methods, involv- 
ing transmission of false signals on the enemy 
radar frequency, also received attention. These 
are generally highly specialized and depend to a 
great extent on the exact characteristics of the 
enemy radar. Some discussion of such methods 
is given in Chapter 12. 


‘ Antijamming Methods 

The use of jamming, confusion, and deception 
methods may be thought of as offensive counter- 
measures, whereas the development of AJ tech- 
niques may be considered defensive. 

A number of AJ methods and devices have 
been developed for communications radar, and 
radio-controlled systems. In many instances, 
these are incorporated in the basic design of the 
equipment involved. This is true of communica- 
tions receivers, since it has been the general 
practice for some time to include features that 
would assist in segregating the desired signal 
from any interfering signals. As new methods 
became available, it was possible and worth 
while to supply modification kits for application 
to some types of existing equipment in the field. 
The best of these devices are of little value, 
however, if not properly used. 

In both communications and radar, there is 
no substitute for experience in reading the de- 
sired signals through interference and for the 
will to do so. The importance of this fact can- 


not be overemphasized. Experience in the field 
has demonstrated that untrained operators do 
not take full advantage of every means available 
to receive the desired signal. A still more serious 
fact is that, upon being exposed to novel forms 
of interference, untrained operators have even 
given up trying to operate their equipment or 
have taken it apart to find faults which were 
mistakenly thought to exist within the set. 
These tendencies can be overcome only by ade- 
quate training and frequent exercises during 
which the operator has an opportunity to fa- 
miliarize himself with the various possible forms 
of interference that may be encountered and 
learns to carry on as well as possible in spite 
of the disturbances. The importance of this AJ 
method is evident when it is realized that by 
proper operator training it may be possible to 
force the enemy to use from two to ten times 
as much jamming power to achieve a desired 
effect. At the frequencies involved, this increase 
is sometimes difficult or even impossible to 
achieve. 

Another potent AJ measure for both com- 
munications and radar is the making available 
of a number of alternate operating frequencies, 
together with means for rapidly changing from 
one to another. The range of available frequen- 
cies should, of course, be as wide as possible 
and the time necessary for making the shift 
should be as short as possible, preferably of 
negligible duration. 

In some instances the incorporation of an AJ 
design feature will be possible only with an 
accompanying impairment in the performance 
of the equipment involved. In general, however, 
it is probably prudent to make some sacrifice in 
performance in order to combat jamming, since 
the finest system is entirely useless if it is suc- 
cessfully jammed. 

A feature which generally improves the AJ 
properties of a system without impairing its 
performance is the use of high directivity or 
resolution. Systems having high directivity are 
more difficult to jam, as a rule, because of their 
discrimination against unwanted signals arriv- 
ing from directions other than that in which 
they are oriented. Microwave sets lend them- 
selves particularly well to improvements along 
these lines. 


SUMMARY 


15 


13 SUMMARY 

The above discussion has dealt with the rela- 
tion between the four basic parts (search, jam- 
ming, confusion and deception, and antijam- 
ming) of the RCM program. Part II of this 
volume deals with technique developments, 
theoretical studies, and test equipment and 


methods which were found necessary for the 
perfection of various RCM applications. Part 

III deals with nonradar applications, and Part 

IV with radar applications. This volume should 
be used in close conjunction with the mono- 
graph®®^ of the Radio Research Laboratory on 
fundamental techniques used in the develop- 
ment of RCM equipment. 




PART II 


TECHNIQUE DEVELOPMENT 



Chapter 2 

NOISE SOURCES AND TRANSFORMERS 


21 INTRODUCTION 

F rom the beginning of the radio counter- 
measures [RCM] program of Division 15, 
it was realized that noise was a good jamming 
signal for all purposes, and later experiments 
confirmed the belief that for many applications 
it was the best one. Investigations into possible 
noise sources were therefore begun very early 
in the program. In January 1943 a thorough 
study of noise sources was organized with the 
establishment of a separate group at Radio 
Research Laboratory [RRL], Harvard Univer- 
sity, for this purpose. 

A laboratory was built up with equipment for 
physical research in photoelectric, gaseous-dis- 
charge, and related noise phenomena. This in- 
cluded a small machine shop, and laboratory 
equipment for the construction, pumping, and 
baking of vacuum tubes. The program that was 
carried out consisted of investigations into noise 
sources of all types (including photoelectric 
tubes, gas-discharge tubes, mechanical sources, 
and others) and the development of noise gen- 
erators, studies of basic processes in noise 
production, development of noise-measuring 
techniques and methods, and investigations into 
video transformers for noise voltages. The re- 
sults of theoretical studies on many of these 
problems are discussed in Section 6.2. 

The greater part of the research, especially 
that of a more fundamental type, was conducted 
at RRL (under contract OEMsr-411), but a good 
deal of development work, especially on specific 
tube types, was carried out chiefly by the 
Radio Corporation of America (under contract 
OEMsr-1060), the General Electric Company 
(under contract OEMsr-931), also by the Bell 
Telephone Laboratories, Inc. (under contracts 
OEMsr-778, 940, and 966), and the Ballantine 
Laboratories (under contract OEMsr-1176). 

In October 1943, a conference was held at 
RRL of representatives of interested industrial 
and government laboratories (including most of 
those mentioned above) to discuss problems of 
noise generation. Reports were presented sum- 


marizing the noise research at the various 
laboratories,®^® and a procedure was instituted 
for the dissemination of complete noise infor- 
mation by the National Defense Research Com- 
mittee [NDRC] among the Division 15 
contractors concerned. It was pointed out that a 
satisfactory noise source would be one which 
was stable, which had a uniform frequency 
characteristic, and which could replace one or 
more video stages in existing noise amplifiers. 


2 2 PHOTOELECTRIC NOISE SOURCES 

One of the first noise sources used in pro- 
duction equipment was the photomultiplier 
tube. The RCA 931 tube was found to be par- 
ticularly good for this purpose, and an investi- 
gation of its characteristics was initiated. The 
conclusions drawn from this study led to re- 
search into better types of photomultipliers, 
which in turn resulted in the development of 
the improved 931A tube. The 931 and later the 
931A were widely used as noise sources through- 
out World War II. 


Research on the 931 Photomultiplier 

The use of the 931 photomultiplier tube as a 
noise source was first proposed in the spring of 
1942.^^® This idea was based on the fact that the 
photoelectric current emitted by the cathode of 
a photocell has a variational component due to 
random emission — that is, a shot effect. The 
mean-square noise current at the cathode is 

^ = 2e^^h, ( 1 ) 

where e is the electronic charge, 7^. is the direct 
current at the cathode, and A/ is the frequency 
bandwidth of the noise under consideration. 
This initial noise current is amplified by the suc- 
cessive stages of the multiplier to give the 
anode current. If the gain of the tube is M, the 
mean-square noise anode current is 

P = 2eAfM^h = 2eAfMlB, (2) 


19 


20 


NOISE SOURCES AND TRANSFORMERS 


where is the average value of the anode cur- 
rent. Thus, the noise current at the anode is 
proportional to the mean current at the anode 
and to the gain of the tube for a fixed band- 
width. For a fixed divider voltage, the anode 
current can be varied within limits by varying 
the illumination at the cathode, whereas the 
gain M is a characteristic of the individual tube. 
The high value of M made the tube a relatively 
high-level, compact noise generator. The 931 
tube was the standard noise source for jamming 
purposes for a long time. 

In an extensive study^^^ of the noise charac- 
teristics, it was found that the value of M, 
measured under standard conditions of light 
and voltage‘s at the time of manufacture, was a 
reliable indication of the performance of the 
tube as a noise generator. Tubes having widely 
different values of M were tested in a number of 
jamming transmitters (RC-156, AN/APQ-2, 
RC-183, and AN/APT-1). It was found that 
tubes having an M of 75,000 or greater would 
operate those particular transmitters satisfac- 
torily. After a series of conferences with RCA 
and Service representatives, a new set of joint 
Army-Navy specifications were drawn up giv- 
ing the number 931A to tubes having gains of 

75.000 or over. At this time from 15 to 20 per 
cent of the tubes manufactured fell below this 
level. A research and development program was 
initiated at RCA, primarily aimed at the im- 
provement of the 931 type of tube. 

Both theoreticap 22 ^nd experimental®^ stud- 
ies of the 931 at RRL demonstrated the impor- 
tance of using a high supply voltage, preferably 

1.000 V, and a voltage divider for the dynodes 
having sufficient current capacity to prevent 
nonuniform distribution of voltage (see Section 
6.2.3) . The use of too small a voltage across the 
last stages results in excessive space charge, 
which reduces the noise output and also distorts 
the spectrum. Under optimum conditions the 
931 noise spectrum is flat over a wide frequency 
range®®® (up to 500 me). The most disturbing 
characteristics which were revealed were the 
erratic operating and aging effects. It was 
found that during the first 15 min of operating 
the noise output decreased by as much as 15 db. 
Further operation resulted in a relatively slower 

a Illumination of 0.001 1, and 100 v per stage. 


rate of decrease.^^^ The tube generally recovered 
after a period of inoperation, but the output 
seldom returned to the original value. Thus, 
there is a short-time high rate of decay and a 
long-time aging effect involved in the use of 
this tube. It was found that the output could be 
restored to nearly its original level by readjust- 
ing the light after the first 15 min of operation. 
It was recommended that this be done with all 
transmitters before the final tests were made. 
The spectrum and noise output were found to be 
independent of temperature between — 50 C and 
+80 C. 

Another multiplier tube in the experimental 
stage, the Bell Telephone Laboratory D159076 
photomultiplier, was also studied. The fewer 
dynodes resulted in a lower overall gain than 
in the 931, and the noise output was 25 db 
below the minimum level set for 931A tubes. 
Only one tube was available for test. 


^ Development of the 931 A 

Photomultiplier 

The tube research program mentioned above 
resulted in the development of the improved 
RCA 931A photomultiplier, which replaced the 
931 and was widely used in various counter- 
measure applications. 

At the time the project was started, the gain 
of the 931 was distributed about a median value 
of 400,000, with a minimum acceptable value of 
12,000. About a year later the median gain was 
at 2,000,000 with an occasional tube at 10,000,- 
000. The life characteristics were also greatly 
improved.^®® When first announced, the 931A 
had a 3:1 minimum gain advantage over the 
931. By 1945 the average product had been im- 
proved by a factor of 5 in gain or equivalent 
noise output. At the same time, the life of the 
average tube was increased by a factor of 3. 

In the general investigation of multiplier de- 
sign298, 299 II shown that minor improve- 
ments could be obtained by alteration of the 
mechanical structure affecting the electron op- 
tics. This accomplished a reduction in noise 
limiting space charge, but the change was not 
considered to yield improvement justifying de- 
layed production. Similarly, longer life was 


GAS-DISCHARGE NOISE SOURCES 


21 


shown to be obtained by substituting more 
rugged, but less sensitive, secondary emission 
surfaces in the last, current-carrying stages; 
again the improvement did not justify compli- 
cations of production. If complete redesign had 
been practicable, it was shown, an increased 
number of secondary emission sources would 
have yielded an increased noise output with no 
increase in applied voltage. 

A detailed study was made of the possibilities 
of regeneratively increasing noise in a special 
photomultiplier in which a grid had been intro- 
duced between the photocathode and the first 
dynode.^^® A large transconductance-to-current 
ratio of 10 was obtained in this construction 
when it was operated with light of long wave- 
length. The noise output of this grid-controlled 
photomultiplier had a peak in the spectrum 
which could be located at various frequencies. 
Regenerative gains in noise were demonstrated 
to be of the order of 10 db in bandwidths of 2 me 
up to 5 me, with unexplored possibilities to 30 
me. However, no use could be found for this 
tube for jamming purposes. For the present, the 
development of the photomultiplier is consid- 
ered completed, particularly for wide-band ap- 
plication. If a new program on multiplier 
development were begun, it would be profitable 
to consider increasing the number of secondary 
surfaces. The field of gaseous discharge seems, 
however, to be the most promising generally for 
noise development. 

2 3 GAS-DISCHARGE NOISE SOURCES 

A major portion of the noise research was 
devoted to the study of the noise characteristics 
of gas-discharge tubes. This involved both fun- 
damental research on the nature of the proc- 
esses involved and practical studies of the best 
tubes and methods of using them. 

Fundamental Research 

The research on gas discharges disclosed sev- 
eral new processes."^^® It was confirmed that the 
strong, nonsinusoidal oscillations which are 
present in hot-cathode arc tubes are plasma 
oscillations. The 1-f noise and such h-f noise as is 


present were attributed to fiuctuations in posi- 
tion and in density of the space-charge regions 
near electrodes. 

The great increase in h-f noise when a trans- 
verse magnetic field is used was shown to be 
produced primarily by a narrow region, very 
close to the cathode, in which the positive-ion 
space-charge density is high and the gradient 
of density is also high. Electrons emitted by the 
cathode are caused by the magnetic and elec- 
trostatic fields to move in curved paths which 
return them to the cathode, as in a magnetron 
at cutoff, if no collisions are made with gas 
atoms. Most of the ionization occurs in a narrow 
zone in which the electrons are moving parallel 
to the cathode. This region is believed to pro- 
duce h-f noise components according to the 
equation for plasma-ion oscillation 

/ = 2VZ, (3) 

where n is the ion density. Since the space- 
charge density has a high peak in this region, 
each segment would have an oscillation fre- 
quency and amplitude characteristic of its den- 
sity. The peak-to-peak voltages developed are 
from 0.5 to 0.9 of the arc drop, which is, in turn, 
of the order of the least ionization potential of 
the gas. 

When cathodes are improperly activated, 
atoms of barium may be sputtered off the sur- 
face of the cathode. These atoms have a much 
lower ionization potential than argon, so that 
electrons quite close to the cathode will have 
sufficient energy to ionize them. Thus, the ioni- 
zation region will be spread over a considerable 
distance. This will reduce the value of the 
space-charge density and lower the h-f noise 
components. Proper activation of the cathode 
eliminates these impurities and restores the 
noise-level characteristics of the gas for the 
values of current and magnetic field used. Be- 
cause of the complexity of the phenomena, the 
reader is referred to the complete report.'^^® 


Audio Noise Sources 

A number of early investigations were made 
into the use of gas tubes as audio noise 
sources.®®’ ^®^’ ^®®’ ®®® One such study 


22 


NOISE SOURCES AND TRANSFORMERS 


considered the possibility of employing Tungar 
bulbs for this purpose it was concluded, how- 
ever, that other tube types were better. Other 
studies led to the conclusion that the Types 2050 
and 2051, and also the Type 884, were particu- 
larly suitable as sources of audio noise.^®-^^^ 
These results brought about the development of 
several a-f noise generators. 

Audio Noise Generator (Gaston) 

One of the first audio noise generators, known 
as Gaston, was developed originally at the Bell 
Telephone Laboratories, Inc. As a result of 
early work on gas-tube noise generation,^® the 
Gaston was designed with a Type 2050 tube as 
the noise source.^^® 

Modifications to this design were made by 
Jansky and Bailey, to obtain a noise source for 
use in their vulnerability testing work“^® (see 
Sections 8.2.3 and 9.3). 

Development of the device to the production 
stage was carried out by the Ballantine Labora- 
tories.^®® This version of the Gaston consisted 
of a 2050 tube, transformer coupled into a 
single amplifier stage and operated directly 
from the standard 28-v d-c aircraft power sys- 
tem. The frequency range of the noise output 
was from 200 to 9,000 c, and the device deliv- 
ered a maximum of 1.4 v to a 100-ohm load. It 
was used to modulate a standard radiotelephone 
transmitter by feeding the output into the 
microphone jack.^®®>^®^ 

Magnetic Audio Noise Generators 

On the basis of the work discussed below on 
the use of magnetic fields with hot-cathode arcs, 
two noise generators'”^ were constructed to pro- 
duce a fiat noise spectrum in the range 500 c to 
100 kc. These consisted of a 6D4 noise unit (see 
Section 2.3.4 below), a low-pass filter to remove 
high-level noise above 100 kc, and an amplifier. 

In one unit, the amplifier was a single stage 
using a 6SN7 and a 4,000-ohm load ; it gave an 
output of 180 V peak to peak. The other unit 
used one triode of a 6SN7 as an amplifier and 
the other as a cathode follower to generate 5 v 
peak to peak across 100 ohms. This latter gen- 
erator was designed to operate into the micro- 
phone jack of a standard communications trans- 
mitter. 


^ ® ^ Study of Commercial Tubes 

In addition to the investigations mentioned in 
the preceding section, a number of studies were 
carried out on the properties of commercial gas 
tubes as sources of video noise.^^^* 2®®- ®®^’ ^®® 

Studies of the Type 884 

The early work consisted of several investiga- 
tions of the Type 884 hot-cathode arc tube and 
similar tube types (including the 816, the 2050, 
and the 2051). Studies of the 2050 and 2051 
tubes indicated that the noise output of these 
types fell off too rapidly at higher frequen- 
cies for them to be useful as video noise 
sources.®®"’ ®®® 

The 884 (and the 816) at first seemed to be 
the most promising. These tubes were shown 
to have relatively high-level noise output up to 
about 1 me; at higher frequencies the noise 
decreased rapidly.^^^’ ®^® Special versions of the 
884 were examined®®^ which contained various 
gases at various pressures, and the effect of 
using a transformer output coupling was in- 
vestigated. 

The variation of noise output from the 884 
was studied in some detail with respect to pres- 
sure changes ; it was shown that maximum noise 
for argon-filled tubes in the 2.5- to 5.0-mc band 
occurred at approximately 300 \i of mercury, 
with or without a magnetic field which aided in 
suppressing unwanted sustained oscillation.-®® 
Other gases were tried and the best results were 
obtained with helium at 700 |i, which, with a 
field of 80 gauss, gave a noise output equal to 
that of the argon-filled tubes with a 50-gauss 
transverse magnetic field. An attempt was made 
to interpret the source of the gas-tube noise and 
it was shown that random fluctuations in glow 
light output were directly related to the current 
fluctuations in the discharge in the frequency 
range, at least to 5 me, a fact considered to be of 
significance in the understanding of the noise 
source. 

In general, in the absence of a magnetic field, 
very strong sinusoidal oscillations were present. 
These oscillations are characteristic of the dis- 
charge and independent of external circuit pa- 
rameters. They were as much as 40 db above 
the noise level and shifted in frequency from 


GAS-DISCHARGE NOISE SOURCES 


23 


tube to tube. The oscillations interfered seri- 
ously with the use of these tubes for noise 
generators. 

Other Tube Types 

It was discovered, however, that a transverse 
magnetic field would suppress the oscillations of 
many types of hot-cathode arc tubes and would 
also greatly increase the h-f components of the 
noise output. With this discovery a large num- 
ber of commercial tubes were studied^®^ in an 
effort to find the best possible source among 


Video Noise Sources 

With the advent of the 2C4 and 6D4 minia- 
ture gas triodes the search for a suitable com- 
mercial tube ceased. The small size of this tube 
and the relatively low value of magnetic field 
required for optimum noise performance made 
it a very satisfactory noise source. 

6D4 Noise Unit 

The development was undertaken, therefore, 
of a unit noise source using the 6D4 in conjunc- 



tubes already in manufacture.^^®* 

468, 473, 566, 639, 672, 769 results of this study are 
summarized in Tables 1 and 2. Typical noise 
characteristics of four commercial tubes are 
shown in Figure 1. 


tion with a magnet. A small electromagnet and 
a permanent magnet were designed at RRL.^’^^ 
These magnets produced a flux density of 375 
gauss at the tube. This noise unit made an ex- 
tremely stable source, with variations of the 


24 


NOISE SOURCES AND TRANSFORMERS 


order of 1 db from tube to tube and practically 
no aging.^ The relatively high noise output made 
possible the saving of one and in some cases 
two stages of video amplification in the noise 
modulators. At the end of World War II this 
noise unit had replaced most of the 931 sources 
in jamming modulators being manufactured. 

This unit was a compact and reliable source 


of the unit. In the GE unit a ring magnet fitted 
concentrically over the 6D4 tube has been sub- 
stituted for the two Alnico slugs. The ring mag- 
net was mounted in a spun or die-formed circular 
aluminum housing consisting of a lower shield 
base, to maintain the magnet and tube socket in 
the preferred orientation, and a removable alu- 
minum cover. This design required less mount- 


Table 1. Summary of noise and oscillation characteristics of commercial gas tubes without transverse magnetic 
field. 




Oscillation 


Noise level (db) 

♦ 

Rms noise 
voltage 

References 

Tube 

Current 

(ma) 

Fundamental 
frequency (kc) 

Amplitude 

(db)* 

50 kc 

1 me 

5 me 

4 me 


Shot noisef 

150 



-14 

-14 

-14 

41 mv 



10 



-26 

-26 

-26 

13 mv 


884 

40 

180 

76 

66 

70 

35 

0.91 V 

346, 468 


3 

440 

76 

24 

22 

-8 



2A4G 

100 

450 

52 

50 

24 

-5 

0.06 V 

566 

WL629 

40 

210 

85 1 

44 

58 



566 

WE256A 

75 

120 

51 

38 

40 

-4 

0.4 V 

566 

RK62 

1.5 

650 

34§ 

— 

1.0 

< -10 


566 

2050 

90 

150 

84 

60 

51 

14 


639 


3 

90 

78 

36 

14 

< -10 



6Q5G 

40 

550 

73 

45 

50 

17 


— 

FG178A 

125 

100 

78 


38 

0 


348 

2D21 

41 

85 

94 

«80 

54 

18 


383 

816 

125 

170 

67 

«60 

37 

9 




*Zero level = 10 /iiv/kct 

tTemperature-limited diode with 3,000-ohm plate resistor. 
tSecond-harmonic amplitude 90 db. 

§Probably another nonharmonic peak below 100 kc. 


of noise in the range from 0.1 to 5.0 me for the 
initial stage of a modulator of a jamming oscil- 
lator. The field was provided by two collinear 
Alnico slugs mounted on opposite sides of the 
tube. 

Redesign of the GBU Noise Source. In order 
to improve the mechanical design and reduce 
the weight of the unit developed at RRL, the 
General Electric Company undertook redesign 

^ Final design of assembly manufactured by the 
Cinaudagraph Corporation, Stamford, Conn., as 
Catalog No. 80-375. 


ing space, provided better shielding, and re- 
duced the weight from 9 to 4 oz. 

Flux plots of the ring magnet and of the col- 
linear slugs showed that the- field due to the 
ring magnet was much more uniform over the 
cross section of the 6D4 tube. It seems probable 
that this fact contributed to the uniformity of 
the output spectrum when the 6D4 was operated 
in the ring magnet at fields up to about 575 
gauss. Operation at somewhat higher fields in a 
collinear electromagnet introduced a large oscil- 
lation peak around 0.4 me. Operation at 575 


MECHANICAL AND OTHER NOISE SOURCES 


25 


gauss instead of 375 gauss has the advantage 
that the noise output is enhanced, particularly 
at the h-f end of the spectrum. 

A modulator unit was constructed in which 
the noise unit drove an 807 modulator tube 
through two stages of 6AK5 miniature pen- 
todes; the latter amplified the noise and com- 
pensated for the lower noise outputs at the 
high and low ends of the spectrum between 0.1 


be useful in noise modulation of jamming oscil- 
lators. 

Several varieties of constriction oscillators 
were built and tested, and noise power out- 
puts of 30 w between 0.55 and 5 me and of 4.5 w 
between 0.1 and 0.55 me were achieved for 
power inputs of 125 w. This project was finally 
dropped for the following reasons. 

1. Permanent gases like argon clean up very 


Table 2. Summary of noise characteristics of commercial gas tubes operated with transverse magnetic field. 


Tube 

I 

(ma) 

B 

(gauss) 

Up 

(volts) 

100 kc 

Noise level (db)* 

1 me 

5 me 

Notes 

References 

6D4 

5 

375 

8.2 

63 

76 

38 


384 

(2C4) 

5 

720 


66 

76 

43 


385 


20 

375 


70 

77 

53 

t 

672 









467 

884 

45 

1,050 

5.6 

56 

62 

48 


346 









468 









639 

2A4G 

100 

2,000 

8.3 

60 

60 

40 



WL629 

40 

2,500 

4.4 

71 

69 

43 



WE256A 

75 

2,000 


65 

58 

33 



RK62 

7 

620 


60 

57 

42 

t 


6Q5G 

40 

2,500 


55 

63 

37 

t 


WE323A 

100 

1,800 


62 

44 

8 



2050 

75 

500 


74 

47 

13 

t 

639 

FG178A 

200 

960 

9.9 

82 

70 

43 


348 

2D21 

41 

1,200 

5 

72 

70 

47 

t, § 

383 


30 

700 

5 

70 

64 

46 

t, II 


GL546 

13 

740 


68 

70 

48 


473 


♦Zero level = 10 juv/kcl 

tStandard RRL noise unit, Max = 80 db at 700 kc. 
JOscillation not suppressed. 

§Anode-to-cathode noise. 

11 Grid as anode. 


and 5 me. This modulator delivered about 10 w 
of noise energy to a 1,000-ohm load. 

Constriction Oscillator as a Noise Source 

A constriction oscillator is a gas-discharge 
tube in which the arc passes through a narrow 
constriction between cathode and anode. As the 
arc current is increased, a critical value is 
reached beyond which the tube is unstable. In 
mercury vapor, for example, at 50 C (13 ft pres- 
sure), the critical current for a 0.040-in. circular 
constriction is 0.5 amp, corresponding to a 
current density of 60 amp per sq cm. It was 
thought that the output of such a tube operated 
in the unstable region might include a suffi- 
ciently broad and high-level noise spectrum to 


fast. Mercury vapor can be used but the tube 
output is very sensitive to the mercury vapor 
pressure and hence to tube temperature. 

2. The tube life is only 5 to 10 hr, limited by 
cathode life. 

3. The noise spectrum is nonuniform and 
erratic. 

4. Standard tubes have been found elsewhere 
to be adequate for jamming noise sources. 


2 4 MECHANICAL AND OTHER NOISE 
SOURCES 

A variety of noise sources were tried of types 
other than those discussed above. The more im- 


26 


NOISE SOURCES AND TRANSFORMERS 


portant of these were of a mechanical nature. 
In general, they were discarded as being less 
useful than the electronic sources discussed 
above. 


Mechanical Noise Generators 

Although a considerable number of different 
mechanical methods of producing noise were 
tested, the only one which gave any real hope 



Figure 2. Detail of brush for Confuser-type 

mechanical noise source. 

of success was the so-called Confuser. Among 
the other ideas investigated were the agitation 
of carbon granules carrying a current, two de- 
vices based on electrostatic generator principles, 
and the use of a buzzer. 

Mechanical Confuser 

The Confuser consisted of a carbon disk, or 
cylinder, mounted on the shaft of a small motor 
for rotation. The speed of rotation was rela- 
tively unimportant. (The data of the curves 
were taken for a speed of 1,800 rpm.) A low- 
voltage battery supplies current through a var- 
iable resistor to two brushes bearing on the 
carbon surface. Many kinds of carbon brushes, 
carbon granules, lead shot, copper braid, and 
other devices were tried as current collectors. 
The best response was obtained with wire 
brushes made of No. 38 Nichrome Grade D wire. 
Ten or fifteen strands of wire were used for 
each of the two collecting brushes. The indi- 


vidual strands were about 1 in. long and were 
cemented to a mica support so as to be insulated 
from each other, as shown in Figure 2. The 
brushes should have sufficient resistance so that 
the current in each wire is relatively inde- 
pendent of the current carried by the others. 
Figure 3 is the circuit used. The peak voltage 
depends somewhat on the supply voltage and 
series resistance. Thus, if only one wire is carry- 
ing current and the contact opens, at first the 
voltage across the brush is the arc drop. Then 
if the arc is extinguished the brush voltage 
rises to the battery voltage. 

Output of the Confuser. When the brushes 
are both pressed hard against the surface of 
the rotating cylinder and carry a direct current 
of about 1 amp (much smaller currents may be 
used), the spectrum is as shown by Curve A 
of Figure 4. There are no peaks in the spectrum 
and the curve is smooth, as shown. When a 
light pressure is used, faint sparks develop at 
the ends of most of the wires and spectrum B 
results. When the pressure is very light, spec- 
trum C results. For condition C, very random 
pulses occur; the peaks of the pulses equal the 
battery voltage. This condition of considerable 
sparking sounds like very good audio noise 
when phones are connected across the brushes. 
Unfortunately, no audio analyzer was available 
at the time this work was performed; conse- 



Figure 3. Circuit of Confuser-type mechanical 
noise source. 


quently, audio spectrum can only be inferred 
from the trend of the video spectrum. 

The greatest output voltage at 50 kc is ob- 
tained with a National Carbon C15 disk. How- 
ever, there is no great variation of output with 
carbon. Carbons similar to National Carbon 
SA25 or SA45 sound very good in phones for 
condition C. An aluminum disk was tried, but 
it was found to have somewhat lower impedance 


MECHANICAL AND OTHER NOISE SOURCES 


27 


and less satisfactory noise characteristics than 
the carbon. 

The photograph of Figure 5 shows the ar- 
rangement of parts of a working model. In this 
arrangement the carbon cylinder is mounted 
on the shaft so that the frame of the motor 
serves as one terminal. Some d-c motors pro- 
duce considerable sparking noise. However, this 


a synchronous motor, while current was passed 
through the granules by means of brushes 
bearing on conducting end-plates. Only 1-f noise 
with occasional high peaks was observed for 
currents from 0.1 amp to 3 amp. In another 
device a rotating carbon cone or disk was intro- 
duced into a can of coarse carbon granules, but 
no improvement was observed. 


OUTPUT 

MILLIVOLTS 



Figure 4. Spectra of Confuser-type mechanical noise source under various conditions of sparking. 
Curve A represents no sparking, curve B very faint sparks from all wires, and curve C very heavy 
sparking. Zero level for the decibel scale is taken as 9.38 fiv. 


‘"noise” has strong periodic components as a 
result of the rotational speed of the motor and 
the commutator characteristics. It might be 
satisfactory for some audio purposes. 

Other Mechanical Noise Sources 

A number of other mechanical noise sources 
were tried and abandoned because of lack of 
promise. Among these were ideas for agitating 
carbon granules while they were carrying cur- 
rent. One of these consisted of an insulating cyl- 
inder filled with carbon granules and rotated by 


Two mechanical devices based on electrostatic 
generator principles were tried. One of these 
consisted of a carbonized belt rotating between 
two conducting cylinders which were connected 
to a load resistor and source of direct current. 
No appreciable noise was developed by this de- 
vice. The other consisted of a recirculating air 
stream driven by a small blower and carrying 
fine carbon granules (National Carbon Co. — 
UR80). Copper screens were placed across the 
air blast and connected to a load resistor and a 
power supply, as shown in Figure 6. Thus, par- 


28 


NOISE SOURCES AND TRANSFORMERS 


tides striking one screen would receive a charge 
and lose it when they struck the other, causing 
pulses in the load resistor. This device produced 
atmospheric-like noise with occasional strong 
bursts. The device did not seem to develop suf- 
ficient h-f noise for RCM purposes to warrant 
expending the time that would have been re- 
quired to design an efficient system. 

The noise output of a Speed-X Buzzer (1,000 
c) was measured in the frequency range 50 kc 
to 5 me. The output drops 37 db from 50 kc to 
2 me and then remains constant out to 5 me at a 
level 30 db above 13.6 pv/kei This source is 



Figure 5. Photograph of the Confuser-type 

mechanical noise source. 

too deficient in h-f noise components to be satis- 
factory. 

A rotary spark-gap noise source was designed 
and two models were built.^^^ The devices con- 
tained a pair of disks, one stationary and one 
which rotated, with studs spaced randomly 
around them. The first model employed a single 
ring (with 28 intervals between studs) on both 
rotor and stator, the second used three con- 
centric rings on each (with 28, 20, and 17 
studs). The studs were distributed according to 
a nongaussian exponential law ; after the calcu- 
lation of the proper number of irregular inter- 
vals, the order of the intervals was chosen on a 
pure chance basis. The preliminary tests indi- 
cated good properties as a noise source for com- 
munications jamming but indicated that an 


even greater number of separate stages (sets 
of rings) would be desirable. 


Other Noise Generators 

Among the other types of noise sources in- 
vestigated were the possibilities of using crys- 
tals or semiconductors for this purpose, as well 
as a variety of miscellaneous sources including 
cold-cathode gas tubes. None of these were very 
good, except that an electrolytic interrupter 
circuit offered some promise as an audio noise 
generator. 

Noise in Semiconductors and Crystals 

Some crystals have been reported as noisy 
when conducting in the high-impedance direc- 
tion. The noise level is very low (2 pv/kc^, of 
the order of diode noise with 150-ma plate cur- 
rent (see below). However, the low level ob- 
served in the preliminary tests of crystals, 
thermistors, and resistors justified the abandon- 
ment in the preliminary stage of the investiga- 
tion of these sources in favor of the gas-tube 
sources. 

Electrolytic Noise Sources. Electrolytic con- 
densers give some 1-f fluctuations when operated 
above their rated voltages. Electrolytic solu- 
tions exhibit no appreciable fluctuations. 

The possibility, however, of obtaining random 
pulses of current at audio frequencies by means 
of an electrolytic interrupter was investigated 
in some detail.^^^ The study included the ex- 
amination of the effects on the spectrum and 
output voltage of electrolyte concentration, the 
use of detergents, electrode material and con- 
struction, current density, and so forth. It was 
found possible to obtain outputs of 3 v or 4 v 
rms into a 1,000-ohm load with a spectrum 
essentially flat from 100 c to 16 kc ; beyond 50 kc 
the attenuation was too high for the output to 
be useful. The physical problems involved in the 
design of a compact electrolytic cell providing 
protection against decomposition, gassing, spill- 
ing, and freezing, as well as stability under 
vibration and tilting, caused the project to be 
dropped in favor of the gas-tube audio noise 
generator. 



NOISE-MEASURING TECHNIQUES 


29 


Miscellaneous Noise Sources 

Several miscellaneous types of noise sources 
which were considered and discarded are de- 
scribed in the following paragraphs. 

Cold-Cathode Gas Tubes. The low-pressure 
glow discharge was found to generate noise 
under certain conditions.'^^^ The noise of this 
type of discharge could be increased by a trans- 
verse magnetic field. However, the high voltage 
required to maintain this discharge made it 



Figure 6. Photograph of the air-blast type 
noise source. 


unsuitable for noise generator applications. The 
low-pressure mercury-cathode arc generated 
both noise and oscillations but was generally un- 
satisfactory. This latter tube had two mercury- 
pool electrodes and was used as a “shorting’’ 
bar on a split-anode magnetron tuning bar. The 
action of the discharge caused some random 
shifting of the operating frequency. However, 
the rate of shifting was too low for direct modu- 
lation purposes and there was insufficient time 
to develop the device. A corona tube was con- 
structed with a fine wire inside a glass tube as 
one electrode and the surrounding ground plane 


outside the envelope as the other. This tube 
required high voltage and gave only random 
pulses due to electron avalanches. 

Moving Arc. An attempt was made to develop 
noise by means of a continually moving arc 
operating at atmospheric pressure. A d-c arc 
was established between a carbon disk and a 
brass ring. It was intended to rotate the arc 
around the disk by a radial magnetic field. How- 
ever, it was found that the magnetic field neces- 
sary to rotate the arc would require an exces- 
sively large exciting magnet. Such noise as was 
observed was of low level and apparently de- 
ficient in h-f components. 

Diode. A wide-band (60-mc) amplifier was 
constructed, with a tungsten-filament diode 
(Type CV172) of low capacitance and a cathode- 
follower output stage. Since the noise output 
characteristics of a temperature-limited diode 
(i.e., maximum anode current, as determined by 
cathode emission, is drawn) may be calculated 
analytically, this device was useful in calibrat- 
ing the video spectrum analyzers. 


2 5 NOISE-MEASURING TECHNIQUES 

In order to compare various noise sources and 
to measure their outputs and spectra, tech- 
niques of noise measurement had to be de- 
veloped. This work involved a theoretical analy- 
sis of the nature of noise and the design of a 
number of devices for noise measurements. 

The experience in circuit techniques for noise 
which was gained in this way was applied to the 
development of equalizing circuits for noise 
amplifiers. 


2.5.1 Theoretical Analysis of Noise 

An extensive analysis showed that noise dif- 
fers in many important respects from periodic 
waves and single transients.'^^s Although many 
of these differences have been noted, no com- 
prehensive attempt has been made to outline 
the restrictions necessary in the application of 
standard circuit theory to noise, and to establish 
the basic and useful rules for practical applica- 
tions. 


30 


NOISE SOURCES AND TRANSFORMERS 


In the report on this analysis, frequently 
used quantities of measurement and description, 
such as average, mean square, and peak value, 
were summarized and their application to noise 
and to periodic waves compared. The main point 
of difference is that, whereas for periodic waves 
these quantities are exact and invariant with 
time, for noise they are to some degree diffuse 
and fluctuate with time. Whereas the instan- 
taneous time function of a periodic wave can 
always be expressed analytically (by means of 
the Fourier development), the time function of 
noise generally cannot. Consequently, the only 
quantities available for analysis are time aver- 
ages. 

Theoretical and experimental work on the 
effect of nonlinear distortion on the power spec- 
trum is summarized. The theory developed is 
applied to problems in the measurement of 
noise. In this connection. Section 6.2 should be 
consulted also. 


Noise-Measuring Devices 

In the course of the experimental study of 
noise it was necessary to construct a number 
of noise-measuring devices. 

Video Spectrum Analyzers 

A video spectrum analyzer (HlOO) was de- 
signed for measurements in the range 100 kc to 
9 me. It was essentially a wide-range receiver 
designed to measure noise in this frequency 
range.^^^ A cathode-follower probe provided a 
high-impedance input, and a square-law power 
output meter measured the energy in either an 
11-kc or a 33-kc band. Provision was made in 
the experimental model for a panoramic view 
of the spectrum from 1 me to 5 me. At maxi- 
mum sensitivity the instrument could measure 
a noise input level of 3.5 ^v/kc^ (100-ohm input) 
or 10 piv/kc^ (50,000-ohm input). In operation, 
the actual sensitivity is controlled by means of 
two calibrated attenuators. The gain is constant 
to 1 db from 100 kc to 9 me, and the original 
unit would measure a peak of 5 v without dis- 
tortion. Two of these units were constructed at 
RRL. The analyzer was not designed to meas- 


ure voltages with waveforms having large peak- 
to-rms ratio (such as radar pulses). 

A similar video analyzer^®^ was developed to 
cover from 30 kc to 10 me. It had a bandwidth 
of about 10 kc and at maximum sensitivity 
could measure signals of less than lO^iv. It over- 
loaded, however, with peak voltages of about 
1 V — considerably less than the reported value. 
This equipment was transferred from Ballan- 
tine to RRL, where (since the response was not 
rms) it had to be calibrated with the HlOO 
analyzer. 

In order to assist in the investigation of 931 
and other noise sources, a video spectrum 
checker (H300) was developed.®^*^ This con- 
sisted of a cathode-follower input probe, atten- 
uator, video amplifier (0 to 5 me), low-pass 
filter (0 to 2.5 me), high-pass filter (2.5 to 
5 me), and thermistor bridge bolometer for 
measuring the output current. The device was 
useful in determining the level of noise and its 
trend with frequency. 

Audio Spectrum Analyzers 

Several 1-f spectrum analyzers were devel- 
oped for research and to aid in determining the 
best operating conditions for the 884 used in 
the B3207 modulator. One of these (H500) cov- 
ered the frequency range 500 c to 200 kc,^^^ 
with a measuring pass band of 60 c, which could 
be located anywhere in this range. The instru- 
ment measured the rms value of noise com- 
ponents in the pass band, with a sensitivity of 
100 [iv/kcK The instrument comprises a cathode- 
follower input probe, an attenuator, a high-pass 
filter, one stage of preamplification, a modu- 
lator, and a local oscillator followed by a low- 
pass filter, an 1-f amplifier, and a rectifier and 
meter. 

Another 1-f analyzer*^^^ was designed to ex- 
tend the range of the General Radio Sound 
Analyzer 760 A (normal range 25 c to 7 kc) to 
200 kc. This was accomplished by means of an 
oscillator and a tuned mixer to beat the noise 
at high frequencies down to a fixed frequency 
band in the range of the sound analyzer cen- 
tered either at 500 c or 2,000 c. High input 
impedance was provided by a cathode follower. 
The minimum detectable sine-wave signal was 
0.82 mv. Although intended for the range 7 kc 


NOISE-MEASURING TECHNIQUES 


31 


to 200 kc, the response was flat to 1 db from 
15 kc to 1 me. Since the response of the General 
Radio sound analyzer is not rms, it was cali- 
brated by comparison with HIOO. 

Two other audio analyzers were developed.^^^ 
The first of these covered from 1 kc to 100 kc 
with a bandwidth of either 150 c or 250 c and 
a sensitivity of about 100 pv. The other oper- 
ated in conjunction with a Hewlett-Packard 
wave analyzer, from 200 c to 16 kc. The band- 
width was continuously variable from 60 c to 
360 c, and signals between 0.1 mv and 500 v 
could be handled. 

Peak-Reading Voltmeter 

A peak-reading voltmeter (H205) was de- 
veloped especially to meet noise requirements.^-^ 
The meaning of “maximum value'’ is vague 
when applied to a function, such as random 
noise, whose future progress is unpredictable; 
hence, an arbitrary criterion is required to de- 
fine peak voltage. For pure noise (i.e., with a 
gaussian amplitude distribution), the effective 
peak value is for many applications propor- 
tional to the rms amplitude, which can be ac- 
curately measured with a square-law meter. 
For asymmetric, clipped, highly pulsed (in 
general, nongaussian) noise, however, the pro- 
portionality between rms and effective peak 
amplitude breaks down, and direct measure- 
ment of the peak is required. Furthermore, with 
unsymmetrically clipped noise both positive and 
negative peaks must be measured. For the in- 
strument developed, a practical criterion of 
peak voltage was selected in terms of linear- 
diode clipping. It was found that a diode loaded 
by the input circuit of a cathode follower pos- 
sesses approximately constant-current charac- 
teristics. The circuit constants were chosen so 
that the average load current was small and 
underwent very small variations as a function 
of input voltage. The average output voltage 
defines the “peak” voltage. The voltmeter meas- 
ures peak-to-peak voltages from 1 v to 150 v 
and covers the frequency range 50 c to 30 me. 

Tube Testers 

The investigation of the 931 characteristics 
(Section 2.2) which revealed the great varia- 
tions existing among individual tubes and their 


aging characteristics demonstrated the need 
for a special tube tester for this photocell. The 
931 Tube Tester, Type U400, consisted of a 
light source, voltage divider, and power supply 
for the tube under test which were essentially 
like those of most 931 noise modulators. A video 
amplifier and vacuum-tube voltmeter completed 
the instrument. Provision was made for stand- 
ardizing the 931 plate voltage and anode cur- 
rent so that the noise output voltage was a 
measure of the gain of the tube. 

A checker (H206) was developed'^^® for the 
6D4 tubes so that the manufacturer (Sylvania) 
could ascertain the noise quality of his tubes. 
This device measured the noise output in a 
band centered at 200 kc (characteristic of the 
1-f level) and at 3 me (characteristic of the h-f 
level), and also integrated the noise output for 
all frequencies below 5 me (indicative of the 
“drive”). Improperly activated cathodes could 
be detected by this checker. 

Throughout much of the work, the rms value 
of noise voltage was measured by means of a 
cathode follower with a thermocouple in the 
output circuit. The bandwidth of the unit was 
15 me and it presented the necessary high im- 
pedance at its input terminals. 


^ ^ ^ Noise Equalization 

The noise output of the gas-tube sources, 
such as the 6D4 noise unit, requires both am- 
plification and equalization in order to provide 
a suitable spectrum for modulation.'^^s f^^t 

required the development of techniques that 
departed from the usual video ones. Ordinary 
video amplifiers operate Class A and are ad- 
justed so that they do not have frequency or 
phase distortion or nonlinear distortion. Noise 
amplifiers are overdriven, as a rule, in order to 
get clipped noise; thus, nonlinear distortion is 
present. Compensation networks are used to 
eliminate frequency distortion but not phase 
distortion. 

Equalizing circuits for noise amplifiers must, 
to a large extent, be adjusted empirically be- 
cause (1) grid current is drawn and (2) clip- 
ping589 causes an increase in the 1-f and h-f 
noise components.^^® For raising the h-f noise 


32 


NOISE SOURCES AND TRANSFORMERS 


level, a simple shunt or series peaking circuit 
is satisfactory. The former, serving as the load 
of the first amplifying tube, must be used to 


capacitances. Low-frequency compensation can 
be achieved by using a parallel RC circuit in 
series with the load resistance of the tube. 



FREQUENCY - Me 


Figure 7. Comparison of sine-wave and noise tests of an amplifier. Curve A shows the actual noise 
spectrum; curve B shows spectrum that would be expected from sine-wave tests. (Zero level = 10 piv/kc^.) 



2 3 4 5 6 

ll-M-S VOITS PE* TURH PE* Cm^ 


Figure 8. Effect of sine-wave excitation on core 
impedance and resistance. The following symbols 
are used: © — 200 kc; A — 500 kc; □ — 1,000 kc; 
X — 2,000 kc; and V — 3,000 kc. 


compensate for the drop-off in the spectrum of 
the 6D4 standard noise source. The series cir- 
cuit can be used to compensate for intertube 


Equalization should be done with noise voltage 
and a spectrum analyzer. It is usually not sat- 
isfactory to equalize a noise amplifier by the 
use of sine-wave and ordinary video-amplifier 
techniques, because the dynamic operating con- 
ditions change considerably when noise is am- 
plified. This is illustrated in Figure 7, where 
curve B shows the spectrum that would be ex- 
pected from sine-wave tests of a modulator, 
whereas the actual noise output spectrum was 
as given by curve A. 


2 6 VIDEO NOISE TRANSFORMERS 

Transformers as coupling elements are used 
chiefly in driving push-pull amplifier stages and 
in coupling power stages to low-impedance 
loads. These two applications are widely used 
in a-f amplifiers, and the problems of designing 
suitable transformers in that frequency range 
are well understood. If it is necessary to use 
transformer coupling in a broad-band amplifier 
which must pass frequencies from several kilo- 
cycles to several megacycles, a number of prob- 
lems arise which cannot be answered without 
much investigation of transformer materials. 
If the transformers are required to pass wide- 
band random noise, the problem is further com- 
plicated, since it cannot be assumed that the 
performance of a transformer with sine-wave 
is an accurate index of its behavior with noise 
excitation. 


VIDEO NOISE TRANSFORMERS 


33 


A project was therefore undertaken^^^ 
two general objectives: (1) to make a thorough 
study of the properties of transformer iron at 
frequencies up to 5 me, for both sine-wave and 
noise excitation, and (2) to make use of this 
information to design suitable interstage and 


in the standard Type C core made by Westing- 
house Electric Company. Some measurements 
were also made on Permalloy-ribbon cores of 
similar construction. The other materials stud- 
ied were Monimax and B9W4A, a nickel-silicon- 
iron alloy. These materials were available in 



I 2 3 456789 10 

BANDWIDTH - Me 

Figure 9. Specific impedance of a transformer core as a function of the bandwidth of the exciting noise. 


output transformers for a Class B wide-band 
noise amplifier. 


Transformer Materials 

In general, there are two major points to be 
kept in mind in choosing the type of trans- 
former iron to use. The first is the desirability 
of keeping the power loss in the iron, due to 
both hysteresis and eddy currents, to a mini- 
mum. A theoretical analysis”^®^ of eddy-current 
losses in transformers is described in Section 
6.2.3. The second important point is the desira- 
bility of low current in the transformer wind- 
ings — that is, high exciting impedance, to mini- 
mize copper losses. 

The investigation was confined to relatively 
few kinds of transformer iron. The cores stud- 
ied were supplied by the manufacturers in 
finished form ready for winding. The material 
studied most thoroughly was Hipersil, as used 


standard punchings, which were stacked to 
form cores of the desired size. The thickness of 
the laminations was as follows : 

Hipersil 0.001 in. and 0.002 in. 

Permalloy 0.001 in. 

B9W4A 0.004 in. 

Monimax 0.003 in. 

Experimental Results 

Measurements were made of the exciting im- 
pedance of the cores and of the core losses, for 
both sine-wave and noise excitation. 

Impedance Measurements, Practically all of 
the impedance data were obtained with Type C 
Hipersil cores of various dimensions. For the 
most part the Hipersil was 0.002 in. thick, al- 
though some information was obtained for 
0.001-in. Hipersil. 

The exciting impedance (and resistance) 
was measured as a function of frequency for 
both sine-wave and narrow-band noise excita- 
tion, for a wide range of values of all the param- 


34 


NOISE SOURCES AND TRANSFORMERS 


eters involved. Typical results are shown in 
Figure 8, which gives some impedance values 
for a Hipersil core. These curves were obtained 
with sine-wave excitations and show how the 
impedance and effective resistance vary with 
excitation for different frequencies. The im- 
pedance is very little dependent on excitation. 
This fact simplifies the investigations consid- 


that the impedance is nearly proportional to 
the square root of the bandwidth, as long as the 
frequency is not high enough to permit shunt- 
ing capacities to be important. 

Core Losses. Measurements were made of 
specific core loss as a function of excitation by 
sine waves and by noise. The materials studied 
included Hipersil, Permalloy, Monimax, and 



I 1.5 2 2.5 3 4 5 6 7 8 9 10 15 20 25 30 40 50 60 70 80 90100 

R-M-S VOLTS PER TURN PER Cm^ 

Figure 10. Loss curves for 0.002-in. Hipersil, sine-wave excitation. 


erably. It will be noted that both the impedance 
and the resistance increase with increasing 
frequency. 

The wide-band noise impedance was investi- 
gated as thoroughly as the narrow-band. The 
dependence of wide-band impedance on band- 
width is shown in Figure 9 for one coil. The 
line is drawn to have a slope of 0.5. The near 
coincidence of the points with the line shows 


B9W4A. Typical loss curves for sine-wave ex- 
citation are shown in Figure 10, for 2-mil 
Hipersil. 

Typical core losses for noise excitation are 
shown in Figures 11 and 12. The former is a 
comparison between the losses in 2-mil Hipersil, 
4-mil B9W4A, and 3-mil Monimax. The com- 
parison was made on this seemingly illogical 
basis because these three are available in suffi- 



VIDEO NOISE TRANSFORMERS 


35 


cient quantity to meet production demands. 
The Monimax appears to have the lov^est loss. 
Figure 12 shows the losses in 3-mil Monimax 
with excitations of different noise bandwidths. 
The losses in general decrease as the bandwidth 
is increased at constant excitations ; in fact, the 
loss appears to be inversely proportional to the 


made to separate hysteresis from eddy-current 
losses by combining the results from the theory 
of eddy-current losses with rough estimates of 
the hysteresis losses made on the basis of a 
series of permeability and hysteresis measure- 
ments. The attempt was only partially success- 
ful, but it was possible to obtain approximate 



0.1 .15 .2 .3 A .5 .6 .8 I.O 2 2.5 3 i* 5 6 7 8 9 10 

RMS VOLTS PER TURN PER Cm^ 

Figure 11. Noise losses in various materials for 0.1- to 2.5-mc band. 


square root of the bandwidth. In other words, 
as the energy in the h-f components increases 
at the expense of the 1-f components, the losses 
are due largely to the 1-f end of the noise spec- 
trum. 

The dependence of loss on the excitation and 
the bandwidth appears to be in qualitative 
agreement with the results of the theoretical 
analysis. 

Other Measurements. An attempt was also 


estimates as to the proportional division of 
the losses. 

The effect of a superimposed d-c magnetizing 
force on the a-c losses was checked and found 
to be very small, even when the d-c field was 
many times greater than the a-c. 

It was found also that an air gap in the 
magnetic circuit increases the magnetizing 
force and decreases both the impedance and 
the core losses. 



36 


NOISE SOURCES AND TRANSFORMERS 


Transformer Design 

The information obtained about transformer 
iron is directly applicable to transformer de- 
sign in general. The transformers discussed in 


formers for use in a Class B power amplifier for 
noise. The required bandwidth was 2.5 me, and it 
was desired to obtain 350 w of noise power in a 
50-ohm resistance load. The power stage was to 
consist of four 813 tubes in push-pull parallel. 



EXCITATION - VOLTS PER TURN PER Cm^ 

Figure 12. Noise losses in 0.003-in. Monimax for various bandwidths. Excitation measured in rms volts. 


this section were intended to be used in a Class 
B modulator with wide-band noise excitation. 
There are thus a number of complicating prob- 
lems to be solved simultaneously. 

The method of approach to the problem of 
designing a transformer for a specific purpose 
is illustrated by the work done in developing 
two transformers for a noise amplifier.'^^^ 
development is therefore described here in some 
detail. 

Design of Transformers 

It was desired to design two different trans- 


The interstage driver or preamplifier output 
tube was a single 813. 

The design of the interstage transformer was 
not carried to the optimum point because the 
proper impedance on the secondary side was 
never definitely determined. There were prob- 
lems involved here of clipping in the preampli- 
fier and in the grid circuit of the push-pull 
stage. Much work remained to be done in bal- 
ancing the various conflicting factors. 

The particular transformer used in these 
tests was of shell-type construction, using four 
2-mil Hipersil cores (V 2 xi/ 2 -in. cross section. 


VIDEO NOISE TRANSFORMERS 


37 


i/ 2 xl%-in. window) . The impedance seen by the 
secondary was arbitrarily chosen as 4,000 ohms, 
shunted by the indeterminate effective resist- 
ance of the grid circuit. Experience indicated 
that the total effective grid-to-grid impedance 
was about 3,500 ohms. A resistance of about 
3,500 ohms was found to be a suitable plate 
load for the driver 813, so a total turns ratio 
of unity was chosen. Of course, the 4,000 ohms 
chosen for the secondary could have been de- 
creased with decreased output voltage, or in- 
creased with decreased bandwidth. The pri- 
mary consisted of 120 turns of No. 40 Formax 
wire, reverse-wound and paralleled; and the 
secondary consisted of 120 turns of No. 36 
Formax, center-tapped. The core impedance at 
100 kc was 37,000 ohms. The exciting voltage 
across the primary was 735 v rms. This voltage 
should result in a core loss of about 9 w. Fur- 
ther investigation of the effects of clipping in 
the preamplifier showed that a lower excitation 
voltage was adequate to produce the required 
power output. Unfortunately, time did not per- 
mit completion of a design to meet the new 
specification. 

The design of the output transformer was more 
straightforward because the secondary voltage 
(132 v) and load resistance (50 ohms) were 
specified. From consideration of the tube char- 
acteristics, a plate-to-plate impedance of 3,200 
ohms was thought desirable, so the turns ratio 
was fixed at 8. The primary excitation voltage 
obtained by multiplying the corrected secondary 
voltage (to account for losses) by the turns 
ratio was 1,225 v. Monimax was chosen as the 
core material because of its low losses. The 
limited selection of available Monimax punch- 
ings forced the choice of a core having a mag- 
netic path about one-third longer than was 
required by a reasonable winding length. The 
longer path would require a lower excitation 
E in order to keep down the total losses. If 
E/NA is taken very conservatively as 1.5, NA 
must be of the order of 800 ampere-turns. The 
exciting impedance Z was chosen to be about 
30,000 ohms. The value of Z/N-A for Monimax 
at 100 kc was found to be 0.64, so that N-A 
must be of the order of 5xl0'^. Solving for 
N and A, one obtains values of 60 turns and 
12 sq cm, approximately. Actually, it was found 


that a somewhat larger number of turns could 
be used without disturbing the h-f character- 
istics. The number of primary turns was set at 
80, with 10 turns on the secondary, so that a 
smaller amount of iron could be used. The cross 
section chosen was 9.65 sq cm. The primary was 
wound with No. 38 Formax, while the secondary 
was wound with No. 24 Formax and contained 
two windings of ten turns, reverse-wound. 

A feature of these transformers was the 
insulation used between windings. The usual 
dielectrics were found to be unsuitable because 
of the h-f loss characteristics and the low maxi- 
mum temperatures tolerated. The insulation 
finally used was Poly F-1114 (Teflon, a low-loss 
material with high dielectric strength 1,000 to 
2,000 V per mil) and a maximum tolerable tem- 
perature of 300 C. Teflon is available in tape 
form of any desired width, with a minimum 
available thickness of 5 mils. Two thicknesses 
of the 5-mil tape were used in each transformer 
to separate the windings. This permitted very 
low leakage reactances, although the capaci- 
tances were undoubtedly somewhat increased. 
The optimum thickness must be obtained by a 
trial-and-error process. Since the Teflon is very 
slippery and does not adhere to any known 
cement, it was necessary to devise special 
clamps to hold the insulation in place. The 
clamps were also used as terminal boards for 
the winding ends. 

Tests of Transformers 

The transformers described above were tested 
for frequency response, loss characteristics, 
temperature rise, and overall performance. The 
preamplifler stage consisted of a 6D4 gas-tube 
noise source, followed by a 6AB7, a 6L6, and 
an 813. The modulator stage contained four 
813 tubes in push-pull parallel. The preamplifier 
design was based on much experience with simi- 
lar circuits used in Class A modulators. 

The transformers appeared to be satisfactory 
in their ability to transform the required 
amounts of power with good fidelity and with- 
out excessive losses. It was not possible to 
obtain adequate spectrum measurements on the 
high-impedance sides of these transformers be- 
cause of distortion introduced by the shunting 
capacitances of the measuring equipment. A 


38 


NOISE SOURCES AND TRANSFORMERS 


lack of flatness in the spectrum was caused by 
the preamplifier. It was not found possible to 
obtain a flat spectrum at the required power 
level, i.e., 350 w. The actual sine-wave response 
of the transformer was flat to within 2 db over 
the required range; however, the effect of the 
various causes of distortion was to make the 
overall spectrum produced flat only to within 
5 db over the frequency range. 

The actual power lost in the transformers 
was measured in a crude calorimeter which was 
probably accurate to at least 20 per cent. With 
a load power of 380 w, the output transformer 
had a loss of about 45 w. The total input power 
to the plates of the push-pull tubes was 840 w. 
Hence, the plate dissipation was about 415 w, 
which is just about the limit for four 813's 
(rated dissipation, 100 w per tube). The plate 


efficiency was about 51 per cent, with an overall 
plate-circuit efficiency of 45 per cent. The losses 
measured in the input transformer for this con- 
dition were about 6 w. 

A second check on the heat loss was made 
with the transformers immersed in oil in cop- 
per cans to simulate actual operating conditions. 
The output transformer was placed in a can 
4x6x7 in. and the interstage, in a can 4x3%x3% 
in. The transformers were allowed to run for 
about an hour until approximately steady-state 
conditions prevailed. The final temperature for 
the output transformer was 64 C and for the 
interstage, 55 C. These temperatures were meas- 
ured at the top of the oil, since thermocouple 
measurements indicate that this temperature is 
about the same as that of the core. Room tem- 
perature was about 30 C. 


Chapter 3 

ELECTRON TUBE DEVELOPMENT 


INTRODUCTION 

T he countermeasures work done under 
Division 15 required considerable vacuum- 
tube development work, both in the design of 
new tubes and in the modification of existing 
ones. Most of this work was carried on by the 
General Electric Company (under contracts 
OEMsr-931 and 1019), the Westinghouse Re- 
search Laboratories (under contract OEMsr- 
747), the Federal Telecommunication Labora- 
tories, Inc. (under contract OEMsr-1034 and 
1430), the Bell Telephone Laboratories, Inc. 
(under contract OEMsr-1222), the Litton En- 
gineering Laboratories (under contract OEMsr- 
1357) , the Radio Corporation of America (under 
contract OEMsr-1043), the Radio Research 
Laboratory, Harvard University (under con- 
tract OEMsr-411), and Sylvania Electric Prod- 
ucts, Inc. (under contract OEMsr-1456). 

The work under these various contracts is 
summarized in this chapter. A theoretical study 
of magnetrons is discussed in Section 6.4.1. 

The majority of the tubes developed are de- 
scribed in detail in an RRL monograph.®"^ A 
discussion is given there, also, of the principles 
and methods of operation of these tubes and 
of their applications and the circuits in which 
they are used. For this reason, the discussion 
that follows is limited to a brief outline of 
how the tube development progressed, together 
with tables listing the tubes and their principal 
characteristics. 

All the tubes considered in this chapter went 
through considerable development. A large 
number of other experimental tube types were 
investigated and partially tested, and then 
dropped, either because of technical difficulties 
or because of lack of interest on the part of the 
National Defense Research Committee [NDRC] 
and/or the Armed Services. 

3 2 LOW- AND MEDIUM-POWER TUBES 

Several low-power tubes were developed, in- 
cluding magnetrons and other types, with 


powers of less than 100 w. In addition, a con- 
siderable number of medium-power magnetrons 
were designed, with powers ranging from 100 w 
to 300 w, but mostly about 150 w. 

^ Low-Power Tubes 

The tubes which were developed with powers 
below 100 w included squirrel-cage magnetrons, 
tubes for use in local oscillators and similar ap- 
plications, and parallel-plane triodes and 
tetrodes. The more important ones made by 
the General Electric Company under Contract 
OEMsr-931 and by the Sylvania Electric Pro- 
ducts Company are listed in Part A of Table 1. 
In the same table in Part B are listed medium- 
power tubes also made by the General Electric 
Company and by the Radio Corporation of 
America ; these are discussed at greater length 
in Section 3.2.2, page 42. 

Low-Power Squirrel-Cage Magnetrons 

A project was carried out jointly by Radio 
Research Laboratory [RRL] and Sylvania 
Electric Products, Inc., with the assistance of 
the Radiation Laboratory [RL], Massachusetts 
Institute of Technology (under Division 14), 
for the development and testing of a low-power 
squirrel-cage type of magnetron for use at 
S-band frequencies (10-cm region) 

A considerable amount of work was done in 
determining the mechanism of operation of 
these tubes. A number of modes of operation 
were discovered by use of cold-test measure- 
ments and were verified with hot-test measure- 
ments. The ratio of air gap to copper thickness 
in assembled anodes, the ratio of anode diam- 
eter to finger length, and the size and shape of 
the end cap were all studied as parameters 
affecting the operation of the tube."^^^ 

The equipment used at RRL in these tests 
was finally transferred to Sylvania Electric 
Products, where it was expected that the pro- 
ject would be continued by direct Service con- 
tract. 


39 


40 


ELECTRON TUBE DEVELOPMENT 




Table 1. Characteristics of loW' 

-power 

and medium- 

•power 

electron tubes. 









Max. 

Max. 


Status! 1 


Tube 

Contractor Div. 15 


Approx. 

Approx. Approx. 

Mag- 

anode 

anode 

Type 

at end 


devel. 

RMA and 

proj. 

Tube 

freq. 

c-w 

eff. 

netic 

poten- 

cur- 

of 

of 

Refer- Remarks 

no. 

no. contract 

no. 

typet 

range 

output 

(%) 

field 

tial 

rent 

out- 

World 

ences 


no.* 



(me) 

(w) 


(gauss) 

(kv) 

(amp) 

put! 

War II 







A. Low-power tubes. 






ZP-633 

GE-931 

RP-244A, 

S.A.Mag. 

300-1,500 

25-10 


3,300 

1.2 

0.1 

P.L. 

I 

Section Double-ended. Sim- 



430A 










3.2.2. ilar to ZP-646 













Discontinued. 

ZP-652 

GE-931 

RP-430A 

Mag. 

1,000-3,000 

25 





Coax. 

I 

Discontinued. 

L-14 

GE-931 

RP-396, 

P.P. 

1,500-3,000 

20-10 

10 


1 + 


Coax. 

III 

135 Discontinued. 



430A 

Tri. 










X-6041 

Sylv. 

RP-430B 

Mag. 

3,500-5,500 

50 


2,000 

1.2 


Coax. 

I 






B. Medium-power tubes {Flute project). 




ZP-590 

5J30 GE-931 

RP-244A 

S.A.Mag. 

10-375 

150 

25-55- 

1,500 

2.5 

0.40 

P.L. 

IV 








40 







ZP-646 

5J32 GE-931 

RP-244A 

S.A.Mag. 

90-450 

150 

30-50- 

1,500 

2.5 

0.40 

P.L. 

IV 

Double-ended. 







30 







ZP-666 

GE-931 

RP-244A 

S.A.Mag. 

120-230 

150 

40 

1,500 

2.0 

0.40 

P.L. 

III 

Production com- 













pleted. Similar to 
ZP-590. 

ZP-579 

5J29 GE-931 

RP-244A 

S.A.Mag. 

350-770 

150 

40-20 

1,500 

2.5 

0.40 

P.L. 

IV 

129 

ZP-675 

GE-931 

RP-244A 

N.Mag. 

425-775 

150 

50 

1,500 

2.5 

0.40 

P.L. 

II 

To replace ZP-579. 

ZP-584 

5J31 GE-931 

RP-244A 

S.A.Mag. 

700-1,200 

150 


2,600 

2.5 

0.40 

P.L. 


Similar to ZP-579. 

ZP-676 

5J33 GE-931 

RP-244A 

N.Mag. 

750-1,150 

150 

50-35 

1,500 

2.5 

0.40 

P.L. 

III 

Replaced ZP-584. 

ZP-677 

GE-931 

RP-244A 

N.Mag. 

1,100-1,650 

300 

50-35 

1,500 

2.5 

0.40 

P.L. 

I 


A-131 

RCA-1043 

R P-244 B 


8,500-10,300 100-200 



2.0 


W.G. 

II 

290, 291, 













292, 294, 













295 


♦Contractors and contract numbers: 

GE-931 = General Electric Company; OEMsr-931. 
RCA-1043 = Radio Corp. of America; OEMsr-1043. 
Sylv. = Sylvania Electric Products Company. 


Jin general, anode voltage and current should not simultaneously 
be a maximum. 

§Type of output: 

P.L. = Parallel line. 


Coax. = Coaxial line. 


tTube types: 

Mag-Magnetron 
P.P.Tri = Parallel-plane triode. 
S.A.Mag. = Split-anode magnetron. 
N. Mag. = Neutrode magnetron. 


W.G. = Wave guide. 

1 1 Status: 

I = First research stage. 

II = Concluding research stage. 

III = Preproduction stage. 

IV = Factory production stage. 


Local Oscillator Tubes 

A project was initiated to explore the possi- 
bilities of developing local oscillator tubes capa- 
ble of operating over a very wide frequency 
range. A tuning range of from 3,000 to 10,000 
me with an output power sufficient to operate 
a crystal mixer was required. Ease of manu- 
facture and mechanical ruggedness were im- 
portant requirements. Two tubes, the 2K48 and 
the 2K49, were developed by Bell Telephone 
Laboratories, Inc., and approximately 90 tubes 
were supplied to RRL for comments and for use 


in developing receivers.^^^ 

Description of Tubes. The 2K48 and 2K49 
vacuum tubes were velocity-variation tubes of 
the reflex type employing focused electron 
beams. They required external cavities in the 
form of a tunable coaxial line, the center con- 
ductor of which forms an integral part of the 
tube as supplied. Tuning was achieved by an 
adjustable piston which varied the effective 
length of the coaxial line. This piston could be 
of the positive-contact type or it could employ 
resonant chokes. The tubes required two d-c 
voltages in addition to the normal heater sup- 


LOW- AND MEDIUM-POWER TUBES 


41 


ply, one being a fixed potential of either 1,000 
or 1,250 V and the other being adjustable be- 
tween 0 and 500 v, the exact value varying 
with the operating frequency. The two tubes 
were externally identical; differing only in in- 
ternal design to permit best operation over dif- 
ferent portions of the desired frequency range. 

The electrically significant details of these 
tubes are an electron gun which directs the 
electron beam through a high-frequency aper- 
ture or gap, two copper disks containing holes 
which define this gap, and a repeller electrode 
which produces a reflecting and focusing field 
to redirect the electron beam through the h-f 
gap after a critically valued time of transit in 
the reflex region. The determination of the 
optimum shape and size of these electrodes and 
the mechanical problems associated with their 
construction and assembly to the required tol- 
erances formed a major part of the development 
work.31® 

Special Problems. A number of rather special 
problems were encountered in the design of a 
wide tuning range reflex oscillator which are 
not present in the usual reflex tube. 

In the first place, the efficiency with which 
the r-f gap performs its function is dependent 
upon the length and diameter of the gap and 
upon the beam velocity as these are related to 
the operating frequency, so that a compromise 
design was necessary. 

The electron transit time in the reflex region 
is critically valued and dependent upon the 
operating frequency. It could be controlled by 
the potential of the repeller; but the repeller 
field must also focus the reflected beam on the 
gap, and this requires a definite repeller poten- 
tial conflicting with the transit time require- 
ments. Another compromise is necessary. 

Then there exists a number of discrete 
regions of the repeller potential for which os- 
cillations at any specified frequency can be 
obtained. These regions, designated as repeller 
modes, correspond to electron transit times in 
the repeller field centering around values given 
by 0 = iV -f %, where 0 is the number of com- 
plete cycles at the operating frequency corre- 
sponding to the transit time and N is any 
integer. Only certain of these modes can oper- 
ate with sufficient power to be useful, and the 
frequency ranges of these vary. The most useful 


tube is one in which one mode is particularly 
strong and persists over the entire frequency 
range to be covered. 

The situation is further complicated by the 
fact that there are a multiplicity of different 
frequencies at which any given cavity will oscil- 
late with a fixed tuning adjustment. These dif- 
ferent frequencies lie in different ranges which, 
for the coaxial line cavity, correspond to lengths 
of one-quarter, three-quarter, five-quarter 
wavelengths, etc. Only the first two of these 
ranges are useful, but operation on any others 
interferes with the use of the tube. The princi- 
pal problem in the construction of a wide-range 
reflex oscillator is, therefore, related to the 
proper distribution of the repeller modes and 
of the cavity ranges, so that unfortunate com- 
binations of these do not give overlapping op- 
erating regions. 

Finally, the returned electrons must not be 
allowed to re-enter the gun region or an unde- 
sirable hysteresis effect is produced. This effect 
is manifested by a shift in repeller voltage re- 
quired for operation depending upon the direc- 
tion from which this range is approached. In 
the 2K48 and the 2K49, this effect was mini- 
mized by the use of a different hole size in the 
two gap electrodes. 

Parallel-Plane Triodes and Tetrodes 

The L-14 was a modified version of the 
ZP-572 (RMA No. 2C39) lighthouse triode or 
so-called oilcan tube and was redesigned for 
use at high frequencies in the Peter system (see 
Section 13.3.1). Three important changes were 
made in the ZP-572 structure: (1) The mesh 
grid of the ZP-572 was replaced by a parallel- 
wire grid in which each wire is mounted under 
tension; (2) the grid-cathode spacing was re- 
duced from 0.004 in. to 0.002 in.; and (3) the 
improved transconductance due to the reduc- 
tion of the grid-cathode spacing permitted an 
increase in the grid-anode spacing from 0.020 
in. to 0.045 in. Bench tests showed that these 
changes improved the operation.^^s (gee part A 

of Table 1.) 

The L-14 has found extensive use in the Peter 
system as an amplifier, both in the 500- to 
700-mc range and in the 3,000-mc range. A 
further variation of the L-14 was built for oper- 
ation at 2,000-v anode voltage instead of the 


42 


ELECTRON TUBE DEVELOPMENT 


1,000-v anode potential which is now used. 

Lower-Frequency Versions. A preliminary 
investigation was carried out on the practica- 
bility of scaling the parallel-plane lighthouse 
tube geometry up to achieve high power in the 
frequency range between 100 and 350 me. Sev- 
eral triodes (L-200 type) and tetrodes (L-201 
type) were designed for operation at voltages 
up to 5,000 V and currents up to 2 amp. The 
triode was scaled from the ZP-464 (RMA No. 
2C43). This project was dropped at an early 
stage because of low radio countermeasures 
[RCM] interest and increased pressure on 
other projects; but sufficient experience was 
gained to make it fairly clear that the problems 
involved in scaling the lighthouse structure to 
high power are soluble and that the power out- 
put predicted by the scaling formulas can prob- 
ably be realized. 


^ Medium-Power Magnetrons 

Enemy radar was concentrated, for the most 
part, in the range between 100 and 1,000 me, 
over most of which no standard tubes existed 
capable of generating high continuous power 
for jamming. It was therefore necessary to 
carry on a program of tube development in this 
range, known as the Flute project. At the same 
time efforts were made to extend the frequency 
range upward to cover other possible enemy 
radar developments. The tubes developed under 
the Flute project are summarized below. Part B 
of Table 1 gives the characteristics of the major 
types. 

Split-Anode Magnetrons 

It has been known for some time®^^*^^^ that 
split-anode magnetrons were capable of gen- 
erating considerable power in this frequency 
range. During the period between the invention 
of the split-anode magnetron in 1924 and 1940, 
a number of difficulties were uncovered which 
prevented the acceptance of magnetrons for use 
in communications. 

Drawbacks of Magnetrons. These traditional 
drawbacks were the subject of a comprehensive 
investigation by the General Electric Research 


Laboratories, with the result that great strides 
were made in the design of this type of tube. 
Some of these problems, and their solutions, 
which have been worked out under contract 
OEMsr-931, are as follows. 

1. Power limitations due to decreasing size 
at high frequencies. A split-anode magnetron 
will not achieve an efficiency higher than 20 
per cent or so at 1,000 me unless the applied 
magnetic field is higher than 2,000 gauss. If the 
anode voltage is to remain below 3,000 v, the 
anode diameter must be so small that it is im- 
possible to dissipate large quantities of power 
by radiation or lead conduction. This problem 
was solved by the introduction of liquid cooling. 

2. Filament hack heating. Except at fre- 
quencies so low that the transit time of electrons 
from cathode to anode is a very small fraction 
of 1 cycle, appreciable numbers of electrons 
return to the cathode with energy which they 
have picked up from the h-f fields. This problem 
has been dealt with in two ways: by making 
the cathodes of rugged tungsten wires or spirals 
and by liquid cooling (see also Section 6.5.3). 

3. Glass bombardment at low frequencies. At 
frequencies below 150 me or so in fields of the 
order of 1,500 gauss, electrons escape in large 
numbers from the anode and bombard the glass 
walls of the tube and the electrode seals. This 
problem was solved in two ways, in two of the 
1-f tubes. In one (ZP-590), electrically floating 
shields were mounted on the anode leads; in 
another (ZP-646), a complex system of shields 
across the anode gaps prevented the escape of 
the electrons. 

4. Modulation characteristics. For amplitude 
modulation, the magnetron has two undesirable 
characteristics : the frequency does not remain 
constant with amplitude variation, and the out- 
put cannot be reduced continuously to zero. No 
good technique was evolved for dealing with 
either of these properties, but for jamming they 
are not detrimental. A little frequency modu- 
lation of the carrier improves the spectrum, 
whereas the nonoscillation at low voltages does 
not mar the spectrum, provided the modulator 
can drive the tube back into oscillation without 
an appreciable hiatus in time. 

5. Frequency limitations consistent with tun- 
ability. For jamming applications it was highly 


LOW- AND MEDIUM-POWER TUBES 


43 


desirable that the oscillator be tunable over a 
wide frequency range. This is most easily 
achieved by having part of the oscillator tank 
circuit outside the tube, but at high frequencies 
the usual Lecher wire tank circuit is so short 
that no part of the tank could be brought out- 
side of the vacuum. This difficulty has been 
overcome by the use of an extra internal 
loop, which forms a half-wave line combination 
with the external Lecher wire system. 

Tube Types. Four main tube types were 
employed at medium levels of power (see 
Table 1). 

1. ZP-590 type. The ZP-590 (RMA No. 
5J30) operated nominally over a range from 
175 to 375 me; the lower limit of the frequency 
range, however, was set by the transmitter in 
which it was used. With a suitable external 
tank, the frequency could be run down indefi- 
nitely. The ZP-666 was a tube of the same type 
except that its anodes were loaded with extra- 
capacity plates to cover the frequency range 
120 to 230 me. 

2. ZP-579 type. The ZP-579129 (rmA No. 
5J29) had essentially the same operating char- 
acteristics as the ZP-590. The ZP-584 (RMA 
No. 5J31) was of the same type except that it 
had a smaller internal loop and operated in a 
field of 2,600 gauss. Both of these tubes suffered 
from severe back heating of their filaments. 

3. ZP-6Jf6 type. The ZP-646 (RMA No. 
5J32) was of double-ended construction to per- 
mit the connection of short circuits or capaci- 
ties across the extra pair of leads and thus 
extend the frequency range. Its operating 
characteristics were essentially the same as for 
the above tubes. The ZP-633 in principle was 
the same as the ZP-646 but was scaled down 
to operate (air-cooled) at 25- to 10-w output 
over the range 300 to 1,500 me. It was con- 
tained in a stainless steel shell, with built-in 
magnet pole pieces, and tuned by symmetrically 
sliding shorts on two Lecher wire systems con- 
nected to the two pairs of anode leads. Satis- 
factory operating life was not achieved for 
this tube. 

Future Work. Much remains to be done on 
tubes of this type. All of these tubes were de- 
signed and started for production on an 
accelerated schedule, so that the research pro- 


gram was restricted to work directly applicable 
to the operation of the tubes. It would be very 
desirable to develop a tube in a metal envelope 
with built-in pole pieces. Several unsolved 
problems related to envelope and seal bombard- 
ment by electrons, drop-off in efficiency during 
operation (apparently associated with the 
secondary electron emission properties of the 
anode faces), drop-out of oscillation at low 
levels, and so forth, still remain to challenge 
the magnetron designer. 

High-Frequency Tunable Magnetron 

The A-131 tunable magnetron was developed 
for use in airborne, X-band jammers.-^^* 2®“*’ 

A number of tubes were built, and a fairly 
uniform output over most of the tuning range 
was achieved, although one “hole” existed in 
the spectrum. Difficulties with cracks in the 
mica window seals were overcome by eliminat- 
ing thermal shock during assembly.^^o Cathode 
studies indicated a possibility for simplifying 
constructional problems^®^ (see Table 1). 

Neutrode Magnetrons 

It was discovered at the General Electric 
Research Laboratory that the addition of a 
third electrode to the split-anode magnetron 
structure permits the tube to operate as though 
it were a four-gap tube. Suitable variations of 
this geometry would allow operation equivalent 
to that with six, eight, or more gaps. Since the 
extra electrode is located in an electrically 
neutral plane and presumably operates at zero 
r-f potential, the tube was referred to as a 
“neutrode.” Higher-order operation presented 
several important advantages: h-f operation 
was possible with low magnetic fields ; filament 
back heating was materially decreased; and 
higher efficiencies were realized. 

The basic tube of this type was the ZP-676. 
The tank circuit for this tube operated in a 
full-wave mode. The ZP-676 was to supersede 
the ZP-584 (see above). The ZP-675 is a lower- 
frequency tube of the same type, to supersede 
the ZP-579. The ZP-677 is another neutrode 
covering a higher frequency range (see Table 
1). The ZP-647 and ZP-685, discussed in the 
following section, are also neutrode-type tubes 
(see Table 2). 


44 


ELECTRON TUBE DEVELOPMENT 


Table 2. Characteristics of 1-kw magnetrons (Piccolo project tubes). 


Tube 

devel. 

no. 

Contractor 

and 

contract 

no.* 

Div. 15 
proj. 

no. 

Tube 

typet 

Approx. 

freq. 

range 

(me) 

Approx. 

c-w 

output 

(kw) 

Approx. 

eff. 

(%) 

Mag- 

netic 

field 

(gauss) 

Max. 

anode 

poten- 

tial! 

(kv) 

Max. 

anode 

cur- 

rent 

(amp) 

Type 

of 

out- 
put § 

StatuslI 
at end 
of 

World 
War II 

Refer- 

ences 

Remarks 

ZP-599 

GE-931 

RP-158F 

S.A.Mag 

90-260 

1 

40-55 

1,750 

2.5 

1.0 

P.L. 

III 

Section 

3.2.2 

Similar to ZP-590. 

ZP-647 

GE-931 

RP-158F 

N.Mag. 

240-500 


50 

1,250 

2.5 

1.0 

P.L. 

IV 



ZP-685 

GE-931 

RP-158F 

N.Mag. 

450-660 

1 

50-55 

1,500 

2.5 

1.0 

P.L. 

I 


Turned over to RCA. 
Similar to ZP-676. 

A-132 

RCA-1043 

RP-158D 

M.A.M. 

(4) 

400-700 

1 

60 

1,500 

2.5 

1.0 

P.L. 

II 

292, 296 

Development com- 
pleted. Modifica- 
tion of ZP-685. 

A-133 

RCA-1043 

RP-158D 

M.A.M. 

(6) 

620-930 

1 

50 

1,500 

2.5 

1.0 

P.L. 

II 

292, 297 

Development 

stopped. 

ZP-594 

GE-1019 

RP-158A 

M.A.M. 

(8) 

460-640 

1 

50-60 

900- 

1,650 

4 

0.5 

Coax. 

II 

253, 491 

Discontinued. 

ZP-615 

GE-1019 & 
FTR-1430 

RP-158A, 

158C 

M.A.M. 

(10) 

600-840 

1 

65 

1,000- 

2,000 

4 

0.5 

Coax. 

I 


T ur ned over to FT R . 

ZP-616 

GE-1019 & 
FTR-1430 

RP-158A, 

158C 

M.A.M. 

(10) 

760-1,160 

2 

50-75 

1,500- 

2,650 

5 

0.5 

Coax. 

II 

248, 339 

Development com- 
pleted, by FTR. 

ZP-597 

GE-1019 

RP-158A 

M.A.M. 

(12) 

1,000-1,400 

1 

50-60 

1,500- 

3,350 

4 

0.5 

Coax. 

III 

250, 254 


Z P-838 

Litt-1357 

RP-158B 

M.A.M. 

(12) 

1,250-1,900 

1 

50 

1,500 

5 

0.5 

Coax. 

I 


Discontinued. 

ZP-639 

GE-1019 & 
Litt-1357 

RP-158A, 

158B 

M.A.M. 

(12) 

1,750-2,600 

1 

50-60 

2,000- 

2,500 

5 

0.5 

Coax. 

II 


Development com- 
pleted. 

ZP-612 

(RMA:5J21) 

GE-1019 

RP-158A 

M.A.M. 

(12) 

2,600-3,350 

1 

50 

2,200- 

3,200 

5 

0.5 

W.G. 

II 

632 

Turned over to 
Litton. 

612L 

Litt-1357 

RP-158B 

M.A.M. 

(12) 

2,460-3,610 

1 

50-65 

3,600 

5 

0.5 

W.G. 

III 

337 

Modification of 
ZP-612. 

ZP-693 

GE-1019 & 
Litt-1357 

RP-158A, 

158B 

M.A.M. 
(12 or 16) 

3,400-5,100 

1 

50 

3,000- 

4,000 

5 

0.4 

W.G. 

I 


Development 

stopped. 

L-104 

GE-1019 & 
Sylv. 

RP-158A, 

158C 

M.A.M. 

(12) 

6,950- 

10,400 

0.5 

35 

5,000 

5 

0.4 

W.G. 

I 

263 

Discontinued. 


*Contractors and contract numbers: 

GE-931 = General Electric Company; OEMsr-931. 

GE-1019 = General Electric Company; OEMsr-1019. 

FTR-1430 = Federal Tele. & Radio Corp; OEMsr-1430. 

Litt-1357 = Litton Engineering Labs; OEMsr-1357. 

RCA-1043 = Radio Corp. of America; OEMsr-1043. 

Sylv. = Sylvania Electric Products Company. 
tTube types: 

S.A.Mag. = Split-anode magnetron. 

M.A.M. (N) = Multianode magnetron {N elements), 
tin general, anode voltage and current should not simultaneously be a 
maximum. 


§Type of output: 

P.L. = Parallel line. 

Coax. = Coaxial line. 

W.G. = Wave guide. 

11 Status: 

I = First research stage. 

II = Concluding research stage. 

III = Preproduction stage. 

IV = Factory production stage. 


3 3 ONE-KILOWATT MAGNETRONS 

In April 1943, a program known as the 
Piccolo project was begun at General Electric 
Company with the aim of developing a line 
of magnetrons for jamming purposes, as a 
countermeasure to the German radar systems 


then in use and as preparation against future 
enemy developments in the radar field. 

The tubes were to generate continuous wave 
and were to cover the frequency range 500 to 
10,000 me at a power level which was not com- 
pletely specified but which was to be of the 
order of 0.25 to 1 kw. They were to be capable 


ONE-KILOWATT MAGNETRONS 


45 


of modulation over a bandwidth of about 10 
me, and, since the complete frequency range 
was to be covered continuously, each tube had 
to be tunable over as wide a range as possible. 
Originally, the airborne use of Piccolos was 
foremost, with the consequence that 2 kv was 
set as the upper practical limit of the voltage. 

Throughout the program, the emphasis was 
on speed of development rather than on per- 
fection. For this reason, it was decided that, 
except in special cases, redesign of early tubes 
would not be undertaken in the light of later 
experience. As far as possible the program was 
kept unified, so that there would be as much 
resemblance as was practicable between differ- 
ent tubes, with the object of simplifying the 
apparatus problem. The tube characteristics 
are summarized in Table 2. 

Redesign of Flute Tubes 

At the start of the program, the two-anode 
and neutrode types of magnetrons were already 
under development in the Flute project (see 
Section 3.2.2) for medium powers. It was 
decided, therefore, that an attempt should be 
made to redesign these tubes to operate at the 
higher powers required. 

It was found relatively easy to increase the 
power output of the medium-power types of 
split-anode and neutrode magnetrons to 1 kw, 
without changing the external dimensions of 
the tube. This was accomplished by the use 
of heavy-spiral filament cathodes, larger anode 
blocks, and more complete shielding to prevent 
electron bombardment of the glass. These 
changes generally increased the anode-to-anode 
capacity and loaded the tank circuit so that 
with the usual transmission-line circuit the 
frequency range covered with a single tube 
was not so great as the range covered by the 
equivalent Flute tubes. 

Four basic tube types were thus developed 
for the 1-kw level. These tubes, whose char- 
acteristics are listed in Table 2, were as follows. 

1. ZP-590 type. The ZP-599 was a 1-kw tube 
of the ZP-590 type. It covered the range 90 
to 260 me at voltages up to 2,500 and currents 
of 1 amp, in a magnetic field of 1,750 gauss. 


2. ZP-6U7 type. The ZP-647 was a neutrode 
redesigned for the frequency range 240 to 500 
me, which it covered at voltages up to 2,500 
V and currents of 1.0 amp in a magnetic field 
of 1,250 gauss. 

3. ZP-676 type. The ZP-685 is a 1-kw tube 
of the ZP-676 type, covering the frequency 
range 450 to 660 me at voltages up to 2,500 v 
and currents of 1.0 amp in a magnetic field of 
1,500 gauss. The design of this tube was later 
changed from a neutrode to a true four-pole 
anode structure; it was then known as the 
A-132. This change increased both the efficiency 
and the frequency range. 

4. A-133 type. The A-133 was a six-pole 
multianode magnetron, similar to the A-132 
but covering the frequency range 620 to 930 
me. One operable tube for this range was 

produced.292 . 297 

^ Development of Multianode 
Magnetrons 

There were several considerations which led 
to the development of a series of multianode 
magnetrons in addition to the redesigned Flute 
types. It would have been necessary, at the 
higher frequencies, to use the latter type in 
any case. A structure to operate at the long- 
wave limit of the range did not appear to be 
too cumbersome to be practical. Moreover, the 
Flute (two-anode) tubes were less efficient 
than could be expected for multianodes, and 
at the higher power level of Piccolos efficiency 
became more important. 

In the development of the multianode tube, 
the experience of RL was available to draw 
on. The scaling technique held the hope that 
rapid adaptation could be made of their suc- 
cessful designs to the very different voltages, 
powers, and frequencies required in ROM. 

Summary of Development 

An outline of the development^^! is given 
below. The specific characteristics of the tubes 
can be found in Table 2. 

Number of Tubes. The range 460 to 5,100 
me and 6,950 to 10,400 me was covered by a 
total of nine tubes, eight in the former and 
one in the latter range. This represents an 


46 


ELECTRON TUBE DEVELOPMENT 


average ratio of 1.3:1 between successive tubes. 
The individual tube ranges themselves average 
1.45:1, the lower-frequency tubes up to 1,400 
me averaging 1.40:1 and the higher-frequency 
ones up to 5,100 me averaging 1.5:1. 

Tube Type, Except for the ZP-616, all the 
tubes were of the radial-vane type (see Figure 
1), double-strapped at one or both ends of the 
anodes. The radial-vane structure rather than 
the slot-and-hole was dictated by the need for 
a maximum of inductance and a minimum of 
nonvariable capacitance. (The ZP-616 was un- 



Figure 1. “Corny”-type tuner in experimental 
ZP-594 magnetron. This tube has vane anode, 
broken straps, and overvane loop output. 

dertaken as a separate effort not coordinated 
with the main program.) Axially supported 
cathodes were used exclusively. They gave the 
advantages of symmetry, left one end of the 
cavity free for a symmetrical tuning arrange- 
ment, made rugged construction possible, sim- 
plified assembly, and did not interfere with the 
attainment of sufficiently uniform magnetic 
fields. 

The tubes are essentially all-metal, except 
for the r-f output terminal. 

Magnetic Field Design. With pierced pole 
pieces it was not difficult to design pole shapes 
which gave uniformity of field within ± 2 per 
cent over the interaction space, with a gap 
length not over 2.5 times the anode length and 
a pole diameter slightly less than gap length.^^^ 
Less favorable geometry was often made neces- 
sary by space requirements of individual tube 
designs. In general, experience indicates that 
the fields were designed a good deal more con- 
servatively than necessary. 


Magnetron Output, Jf60 to 2,600 Me. In this 
frequency range a loop coupler feeding out 
through a constant or variable impedance line 
was used. The loop which proved to be most 
satisfactory was of the overvane type (see 
Figure 1), which starts at the edge of a vane, 
extends a short distance parallel to the tube 
axis, then turns and extends radially outward 
to envelope (or casing), where it joins onto 
the inner conductor of the coaxial section of 
the output. The size of the loop determines the 
general level of the tube loading which is 
expressed as the external Q. Several other types 
of loops and other outputs were tried and 
discarded as being less satisfactory than this. 

Magnetron Output, above 2,380 Me. Here a 
wave-guide output was used. The design is 
entirely new. In essence it makes use of the 
principle of the dumbbell cross-section wave 
guide, in order to maintain cutoff wavelength 
and decrease impedance in making the transi- 
tion from the large rectangular guide used for 
transmission to the much smaller cross section 
which can be arranged to couple power out of 
the magnetron cavity. In the ZP-612, the shell 
of this wave-guide transformer tapers from 
the rectangular cross section of the standard 
guide to a 1-in. diameter circle just before it 
joins the magnetron cavity wall (see Figure 2). 
In the same length two coplanar metal vanes 
extend inward from opposite sides of the shell, 
their opposing edges starting from the full 
guide-width separation and approaching to a 
separation of a few mils where they reach the 
inside of the cavity at the roots of the vanes. 
This close approach forms a slot and adds 
capacitive loading to the line. The slot is placed 
midway between two adjacent vanes from be- 
tween which, but inside the output shell, a 
considerable portion of the casing wall has been 
removed so that current flowing from the root 
of one vane to the other cannot flow over the 
casing wall but encounters the impedance pre- 
sented by the slot. 

Tuning Methods. Four tuning methods were 
tried, of which one (with modifications in 
several cases) was universally adopted. 

One discarded scheme was the use of Mumbo. 
This was a section of coaxial line closed at one 
end, the other end of the inner conductor being 


ONE-KILOWATT MAGNETRONS 


47 


terminated in a flat plate which formed a 
variable condenser with a flat flexible end cover 
on the outer conductor. The end cover was 
manipulated through the rigid vacuum envelope 



Figure 2. Early wave guide output for ZP-612 
magnetron showing {top) outer end (from which 
the glass window has been broken out) with 
ramps leading back toward the anode, and 
(bottom) the inner end between roots of (cut- 
off) vanes at circumference of anode structure. 
(The output became inverted between pictures.) 

by a metal bellows. This cavity was joined 
directly to the straps of the tank circuit by a 
section of low-impedance coaxial line which 
pierced the cavity’s cylindrical side wall near 


the latter’s closed end, the outer conductor join- 
ing the side wall and the inner conductor pro- 
jecting in to join onto the inner conductor. 
Thus, Mumbo was effectively a step-up trans- 
former which would convert small changes in 
susceptance at the variable condenser into large 
changes at the connecting line. 

This could have been developed into a prac- 
tical method. It suffered, however, from two 
disadvantages. The circulating energy in 
Mumbo, evidenced by marked heating, caused 
an additional power drain and the line-plus- 
Mumbo system had other modes besides the 
desired one so that the jt mode of the cavity 
was no longer uniquely defined. The result was 
that three distinct modes of oscillation were 
found in operating a tube so equipped. 

A third method which evolved out of the 
principle underlying Mumbo was to achieve the 
transformer action in a straight section of coax 
by expanding the outer conductor and con- 
tracting the inner conductor up to the termina- 
tion in a variable condenser as before. This is 
shown in Figure 1. Here one of the vanes was 
cut down by the diameter of the outer con- 
ductor so that this conductor, projecting 
through the casing, replaced the cutaway por- 
tion of the vane. This was known as '‘Corny” 
because it looked like a cornucopia (and for no 
other reason). On cold test it showed two 
modes and a desirable tuning range. It, too, 
would suffer from additional power loss. It 
was never actually operated because “LC” was 
by that time well under way. 

This last, “LC,” was the generally useful 
tuning method. It arose from the combination 
of two separate methods, the variation of the 
effective capacitance of the tank circuit on 
the one hand and the variation of the effective 
inductance on the other. The capacitance was 
changed by using coplanar straps which had 
been widened radially and opposing them with 
a copper disk or ring, called the C-Ring, which 
was movable toward and away from them (see 
Figure 3). This was modified in the ZP-612 
by not using the straps but by getting the 
capacitance with a system of fingers reaching 
in between the vanes near their tips. The 
ZP-639 embodies the same scheme. 

The variation of inductance was achieved by 


48 


ELECTRON TUBE DEVELOPMENT 


affecting the cross section available to the r-f 
magnetic field in its path through each sector 
and around the edge of each vane into the 
adjacent sector. A plain annulus, called the 
L-Ring, parallel to the plane of the anode, 
which when brought close to the vanes choked 
the field through the outer two-thirds of each 
sector was the earliest form tried. This was 
modified by adding extensions of various depth 
which reach into each sector until, in the L-104, 
the annulus disappeared and the arrangement 



Figure 3. ZP597 magnetron disassembled show- 
ing cathode header with oxide-coated cathode, 
tank circuit with wide straps, and tuning header 
with “LC” tuner, L-Ring being next to header. 
Visual window and output with unformed loop 
are also shown. 

is a ‘‘crown of thorns” adapted to the vane 
structure. 

“LC” consists in having these two tuning 
methods operate simultaneously. Generally, this 
was accomplished by assigning one face of the 
anode structure to the C-tuning, placing the 
C-Ring there, assigning the other face to the 
L-tuning with the L-Ring there, and connecting 
the two together rigidly by metallic rods ex- 
tending through the middle of three or more 
of the sectors. The exceptions are the L-104, 
in which L-tuning only is used, and the ZP-616, 
in which the different anode structure permits 
a single annulus to perform both L- and C- 
tuning functions. 

Cathode, The nickel mesh oxide-coated 
cathode was usable in the ZP-594 and ZP-597 
when they were used at the 2-kv rating. Their 
use was, however, attended by the need of 
rather extreme precautions to keep the end 
hats cool so that they would not emit even after 
being sensitized by the barium which inevitably 


got strewed around the tube after it had been 
run for some time. 

Tests of secondary emitters were unsuccess- 
ful. At 2 kv, temporary operation was obtained 
with one or two such sources, but these invari- 
ably failed after short periods of operation. At 
5 kv, slightly better performance was obtained, 
but it was not of a grade to warrant further 
experimentation in view of the availability of 
hot emitters. 

Most of the ZP-612’s which were made used 
a cathode of overwound tungsten coated with 
thoria wound on a thoria cylinder. The switch 
from the oxide-coated cathode was made be- 
cause the higher operating temperature made 
the thoria-coated cathode better able to with- 
stand the more concentrated back heating 
which resulted from the smaller cathode size. 
This cathode suffered from the difficulty that 
at operating temperature the thoria cylinder 
became sufficiently conductive to short-circuit 
and burn out. 

The development of the Flute series of mag- 
netrons and the independent work on ZP-616 
showed that the simple geometry of the cylinder 
was not a requisite of a satisfactory cathode. 
Among those tubes are many with helical 
tungsten wire filamentary cathodes. Also, the 
change of tube voltage to 5 kv made it doubtful, 
on the basis of previous experience with other 
types of vacuum tubes, that the oxide-coated 
cathodes would stand up. This led to the adop- 
tion of helical tungsten filaments for a number 
of the tubes (in the range 460 to 1,400 me). 

For the smaller cathodes required in the 
ZP-612, it was determined that the requisite 
emission can only be furnished if the properties 
of thoriated tungsten are taken advantage of. 
Accordingly, this tube has a helical thoriated 
tungsten wire filamentary cathode. 

Except for the L-104 all of the cathode helices 
are double-wound so that the current in adja- 
cent turns flows antiparallel. In the ZP-612, 
where the turns are rather closely spaced, this 
is important for mechanical reasons. The mag- 
netic repulsion of adjacent turns gives a 
stabilizing action against the approach of such 
turns toward each other. There is also an im- 
portant electronic effect. The filament-heating 
current in a single helix produces a frequency 


ONE-KILOWATT MAGNETRONS 


49 


modulation (and at low powers an amplitude 
modulation) of the magnetron output. The cur- 
rent counterflow of the double helix greatly 
reduces this effect at the same time that the 
effect period becomes 120 c instead of 60 c for 
the usual 60-c a-c supply. 

A complication in the structure of the 
cathode support, which has nothing to do with 
electron emission, has been found to be neces- 
sary in several cases. This is the use of a 
qitarter-tvave choke to keep power from flowing 
out of the cathode leads. The use of two wide 
straps necessarily of very different radii cre- 
ates an unbalance in the resonant structure 
which excites the cathode with ultrahigh fre- 
quency. This is the case in the ZP-594, ZP-615, 
and ZP-597. In the latter tube, the choke 
creates a difficulty of its own by giving rise 
to a resonance at the short-wave end of its 
range. 

The Midtianode (Piccolo) Tubes, General 
information with regard to each Piccolo tube 
is contained in Table 2. In view of the foregoing 
discussion, this table is largely self-explanatory. 
There are, however, some comments to be made. 

ZP-594 (see Figure 3) was the first tube to 
be developed. It and the L-104 are the only 
tubes with double-ring strapping at both ends 
of the anode. It has completely external pole 
pieces, insulators (quartz) in the LC tuning- 
rod structure, and multiple tuning knobs. The 
plan was to gang these mechanically. Work on 
it was suspended at the model shop stage 
because of the promise of tubes like the ZP-685 
to put out 1 kw of power in essentially simpler 
tubes. 

ZP-615 is an interpolation between the 
ZP-597 and the ZP-594. The LC tuning-rod 
structure is completely conducting. 

ZP-616 represents a deviation from general 
family characteristics. Each spoke of the anode 
is made of a doubled-back piece of copper 
tubing, which is roughly L-shaped with the 
stem of the L radial and the tip of its base 
expanded into a rectangular loop. The base, 
extending into one side of the loop, forms an 
anode face. The strap connections start from a 
second side of the loop, thread through the next 
adjoining loop, and end on a third side of still 
the next loop. This is essentially “echelon” 


strapping. A single annulus serves for tuning. 
In its lowest position, it blocks the flux through 
the sectors formed by the stems of the L's and, 
in its highest position, it adds capacitance by 
its approach to flat pie-shaped lands brazed to 
the third side of the loops mentioned above. The 
annulus is fastened rigidly to the upper pole 
piece and this whole assembly moves axially in 
the tuning operation. 

The effective water cooling of the anode 
faces allows this tube to be given a rating of 
2.5-kw continuous output and necessitates more 
careful attention to the cooling of the output 
seal. Cooling is accomplished by an air blast 
projected against the inner edge of the seal 
from a series of oblique holes in the inner 
conductor. 

ZP-597 was the second tube to be developed. 
ZP-638 was to be an interpolation between the 
ZP-639 and the ZP-597, probably lying closer 
to the 639 because that tube represents a much 
later stage in the general development. 

ZP-639 is patterned to a large extent after 
the 612L. It is the last tube on a decreasing 
wavelength scale in which coax output is used. 
The 612L embodies many features which are 
different from its predecessors, namely, the 
broad-band wave-guide output transformer 
and 707 glass window, plunger C-Ring, tuning 
mechanism actuated by six tuning rods project- 
ing through the magnetic pole outside the pole 
face proper, LC structure rigidly guided by 12 
parallel tungsten rods sliding in copper inserts 
in pole pieces, thoriated cathode, and grounding 
of L-Ring to casing by tungsten spiral. 

ZP-693 has been given no attention beyond 
debating whether to come out into standard 
S-band wave guide or nonstandard lx2-in. 
inside diameter guide. Cathode requirements 
may dictate the use of 16 vanes. 

L-104 has essentially crown-of -thorns tuning, 
with the thorns trapezoidal in shape to fit the 
22V2-degree sectors formed by the vanes. One 
thorn has been left out at the sector from which 
the output leads. Clearance between thorns and 
vanes and between thorns and the walls of 
their channels through the pole pieces is 0.005 
in. The total length of thorn is about 0.62 in. 
and at the short-wave end of the tuning range 
the thorns extend through to the far side of 


50 


ELECTRON TUBE DEVELOPMENT 


the anode, the length of which is 0.236 in. The 
tapered wave-guide output is terminated by a 
0.003-in. to 0.004-in. thick mica window of 
full wave-guide cross section — no attempt has 
had to be made to adjust it for zero reflection 
at the center of the band. 

General Recommendations. The one phe- 
nomenon which the Piccolo work served to 
emphasize and concerning which there is only 
slight empirical understanding is the diode 
cutout. This is a refusal of the tube to oscillate 
in the wanted mode. Whether the tube simply 
goes into a cutoff condition in which it passes 
(practically) zero anode current or jumps to 
another mode depends simply on the relation 
of the power-supply characteristic to the start- 
ing conditions for the other mode and the 
loading of that mode. It is doubtful that the 
loading of that mode has any effect on whether 
or not the original mode quits. 

There appear to be two causes. One is over- 
loading of the tube, in which case reducing the 
external Q either by using a different output 
transformer or by applying a suitable standing- 
wave ratio relieves the condition and permits 
the tube to resume normal oscillation. The other 
cause is a deficiency of electron emission, in 
which case increasing the supply by increasing 
the cathode temperature, for instance, is effec- 
tive. 

This phenomenon should certainly be investi- 
gated with the purpose of explaining its cause 
and mechanism. 

Present Piccolos show frequency shifts ivith 
envelope temperature and loading conditions. 
Means of reducing this should be explored. 

In extending the range of the series toward 
still higher frequencies there are the possi- 
bilities connected with basic shapes of reso- 
nator structure other than the radial, such as 
the cage type, the linear magnetron, and the 
neutrode type. 


3 4 HIGH-POWER TUBES 

Two general types of high-power tubes 
were investigated — magnetrons and resna- 
trons. Both types were found to be satisfactory 


for RCM use, although no large numbers of 
equipments using such tubes were built because 
of the specialized nature of their application 
and the relatively high cost of the tubes and 
associated equipment. 


3-4.1 High-Power Magnetrons 

At power levels above 1 kw, the techniques 
which have been described are no longer ade- 
quate for handling the anode dissipation and 
electronic envelope bombardment or, at high 
frequencies, for dissipating the power due to 
back bombardment of the cathode. Two entirely 
different tube types, the ZP-636 and the ZP-595, 
have been evolved for this power range and 
are described below. 

ZP-636 Type Tube 

This is a double-ended coaxial structure 
which covers the frequency range 85 to 350 
me by sliding shorts symmetrically placed in 
coaxial lines connected at the opposite ends of 
the tube. The cathode is a heavy tungsten spiral 
inserted through an arm which passes through 
the center of one pole of the magnet. This tube 
generates a power output which varies from 
3,000 w at the center of the frequency range 
down to 1,000 w at the ends of the range. Its 
efficiency is about 50 per cent. It operates at 
voltages up to 4,000 v and currents up to 1.0 
amp in a magnetic field of 2,000 gauss. 

ZP-595 Type Tube 

This is nominally a 10-kw tube and will cover 
a 15 per cent tuning range around a center 
frequency which can be set when the tube is 
designed, anywhere between 400 and 1,000 me 
or so. Peak power outputs as high as 17 kw 
have been reached around 500 me. Tuning is 
accomplished by motion, through a vacuum- 
tight bellows, of a plate which changes the 
capacity between the anode segments. The 
cathode is a water-cooled secondary emitter 
which takes the form of a copper bar coated 
with a magnesium alloy. A tungsten filament 
recessed into the cathode face provides enough 


HIGH-POWER TUBES 


51 


electrons to initiate oscillation. Returning high- 
energy electrons supply secondaries in sufficient 
numbers once oscillation is started. The ZP-595 
operates in magnetic fields between 1,000 and 
2,000 gauss, at plate voltages up to 20,000 and 
plate currents up to 1.5 amp. Its efficiency is 
of the order of 60 per cent. 

A variation-^ of the ZP-595 has been worked 
out by the Westinghouse Research Laboratory. 
This tube is identical with the ZP-595 as far 
as its electrical design is concerned. Its tank 
circuit and tuning mechanism have been 
changed, however, to give it a wider tuning 


tubes are required to cover the frequency range 
350 to 700 me. 

The principal difficulty with the above tube 
is limited cathode life. Further improvement in 
elimination of fluorescence of the output seal 
and in coupling power out of the tube should 
also be made before the tube can be said to be 
entirely successful. 

The Resnatron 

Until very recently no tubes were available 
in the range of wavelengths from 300 to 1,500 
me which could deliver more than a few hun- 


Table 3. Characteristics of high-power magnetrons and resnatrons. 









Max. 

Max. 


Statusll 



Tube 

Contractor 

Div. 15 


Approx. 

Approx. Approx. 

Mag- 

anode 

anode 

Type 

at end 



devel. 

and 

proj. 

Tube 

freq. 

c-w eff. 

netic 

poten- 

cur- 

of 

of 

Refer- 

Remarks 

no. 

contract 

no. 

typet 

range 

output (%) 

field 

tialt 

rent 

out- 

World 

ences 



no.* 



(me) 

(kw) 

(gauss) 

(kv) 

(amp) 

put§ 

War II 








High-Power Magnetrons 






Z P-636 

GE-931 

RP-116A 

S.A.Mag. 

85-375 

1-3-1 50 

2,000 

4 

1.0 

Coax. 

I 


Double-ended. Dis- 













continued. 

Mod.*" 34 

West -747 

RP-351A 

S.A.Mag. 

335-500 

10 65 

1,550 

13 

2.4 

W.G. 

II 

23, 24 

No production 













planned. 

ZP-595 

GE-931 

RP-116A 

S.A.Mag. 

450-525** 10 -t-** 60-65 

1,000- 

14-20 

1.3 

Coax. 

II 

130 

No production 







2,000 






planned. Center 
frequency ad- 
justable.** 

Mod.*: 36 

West-747 

RP.351A 

S.A.Mag. 

400-700 

10 65 

1,550 



W.G. 

I 

23, 24 

No production 













planned. Similar 
to Mod. 34. 






Resnatron 







Mod.*; 21 

W'est-747 

R P-353 A 

Resn. 

375-600 

25-1- 75 


15 

5.0 

Coax. 

111 

25, 290 

Demountable. Pro- 


duction completed 


♦Contractors and contract numbers: 

GE-931 = General Electric Company: OEMsr-931. 

We8t-747 = WestinRhouse Research Labs.; OEMsr-747. 
tTube types: 

S.A.Mag. = Split-anode maRnetron. 

Resn. = Resnatron. 

tin Reneral, anode voltaRe and current should not simultaneously be a 
maximum. 

5Type of output: 

Coax. = Coaxial line. 

W.G. = Wave guide. 

range and to permit it to operate into a wave 
guide instead of a coaxial line. A considerable 
number of these tubes have been made, includ- 
ing several variations of the fundamental de- 
sign. The final models are sealed-off tubes, 
which employ Dowmetal-sprayed cathodes. 
These tubes have output seals which are 
specially treated to prevent fluorescence. Two 


llStatus: 

I = First research stage. 

II = Concluding research stage. 

III = Preproduction stage. 

IV = Factory production stage. 

^These were the numbers assigned to the final models. Earlier develop- 
ment models were given other numbers, as referred to in the text. 

**The ZP-59o covers a 15 per cent frequency range about a central fre- 
quency determined by the design of the tube. It can be chosen anywhere 
between about 400 and 1,000 me, and the power output depends upon this 
choice. 

dred watts continuously. In 1938, however, a 
new type of tube (called the resnatron) was in- 
vented which showed promise of becoming a 
good source in this range. In 1940, the tube 
had been developed to the point where it was 
interesting to NDRC and a development con- 
tract was let to the University of California 
by Division 14. The work was continued at the 


52 


ELECTRON TUBE DEVELOPMENT 


Westinghouse Research Laboratories by Divi- 
sion 14 and Avas later transferred to Division 
15, supported by OSRD Contract OEMsr-747. 
Tubes of this type were installed in operational 
ground barrage-jamming stations in the 
European Theater of Operations. This work 
has been reported in detaiU^. 24 ^ brief sum- 
mary of the design features with be given in 
this volume. 

As the operating frequency of vacuum tubes 
is increased, the transit time effects of the 
electrons become increasingly important so that 
a tube to be operated by grid control must 
have closer spacing of elements; but as the 
elements of the tube are decreased in size to 
obtain the closer spacing, the problem of dissi- 
pating heat generated by collision of the elec- 
trons with the different elements of the tube 
becomes serious. As the frequency is increased, 
there seems to be only one possible way of 
avoiding melting the electrodes, that is, by 
keeping the power output of the tube down. 
As a result, many tubes oscillating at high 
frequencies but giving little power have been 
designed. In a tube operating at very high 
frequency, it is impossible to avoid the effect 
of transit time. Rather than attempting to 
avoid this, the resnatron takes advantage of 
the transit time of electrons in such a way 
that larger spacings of the electrodes and lower 
voltages may be used. In this way adequate 
cooling of the various electrodes is made 
possible. 

Another feature of the design is the focusing 
of the electrons in such a way that very few 
of them strike any electrode except the anode. 
Thus, the cooling problem of the intermediate 
electrodes is much reduced. Other features of 
the tube are that the tank circuit and grid 
circuit elements are connected directly to the 
electrodes without intermediate leads and are 
entirely inside the vacuum envelope surround- 
ing the tube. This tends to make the tube large 
at long wavelengths. However, there are no 
external circuit elements involved except the 
output transmission line. 

These fundamental principles of design have 
been incorporated into most of the various 
models of the resnatron which have been built. 
The first tube which gave large c-w power was 


a tetrode designed in 1940 and tested first at 
the University of California. In it were six pure 
tungsten filaments arranged so that the elec- 
trons traveled along the axis of the tube. It 
delivered 8 -kw average power at 860 me with 
an efficiency of almost 50 per cent. This opera- 
tion was very encouraging and the testing of 
the tube was transferred during the summer 
of 1941 to the Westinghouse Research Labora- 
tories, where a more adequate power supply 
and better facilities were made available for 
continuation of the development. The design 
and construction of the power supply took a 
year and the tests on the 860-mc tetrode were 
completed in the summer of 1942. This tube 
required a voltage of 20 kv on the second grid 
(called the accelerator grid) and 25 kv on the 
anode because of the large spacings in the tube. 
It was designed on a strictly experimental 
basis. The tube was demountable and included 
many rubber gaskets and was consequently 
extremely subject to vacuum leaks. However, 
the operation was sufficiently promising to 
warrant further development. The next tube 
which was developed was a triode for wave- 
lengths of approximately 1,500 me. It was not a 
successful tube because, although it oscillated 
and gave about 1 -kw output, its efficiency was 
quite low. The next tube which was developed 
was a tunable tetrode for the wavelength range 
475 to 500 me for use in a ground barrage- 
jamming station as the countermeasure for the 
German night-fighter radar (see Chapter 11). 
This tube, with suitable later improvements, 
proved to be quite satisfactory for the purpose, 
and a considerable number were manufactured 
for operational use. 

Development of a Sealed-off Resnatron 

A project for the development of a special 
tetrode of the sealed-off type giving an r-f 
output power of 3 to 4 kw at 600 me with an 
efficiency of 60 to 70 per cent was undertaken 
by the Federal Telephone and Radio Corpora- 
tion. This tetrode was supposed to be scaled 
down from the higher-power tube described 
above. 

A large number of tetrodes were constructed 
and tested-^^ without reaching the desired 
results (the highest efficiency obtained at 600 


HIGH-POWER TUBES 


53 


me was 30 per cent) . After considerable studies 
and measurements of all the effects involved, 
the following conclusions were reached. 

1. Geometric scaling probably cannot be 
applied to this problem because such scaling 
does not take into account the secondary emis- 
sion of the anode. 

2. The secondary electrons present in the 
screen-grid anode space may have a consid- 
erable effect on the behavior of the tube, even 
though they do not reach the screen grid, by 
absorbing energy from the r-f field. 

3. The methods for suppressing secondary 
electrons used at lower frequencies, such as 
formation of virtual cathodes or introduction 
of a third grid, are probably not adapted to 


ultra-high frequency, where the transit time in 
the screen-grid anode space has to be con- 
sidered. 

4. The early theories of operation of the 
resnatron were probably not satisfactory. The 
success of the resnatron can probably be 
accredited to the high voltage used, which 
minimizes all transit time effects and eliminates 
secondary emission and to the extremely effi- 
cient cooling, which allows very high dissi- 
pations per unit area. 

5. The development was terminated before 
all methods of suppressing secondary emission 
had been fully investigated. Additional develop- 
ment work in this field is certainly warranted. 



Chapter 4 

ANTENNAS AND RADIO-FREQUENCY POWER TRANSMISSION 


INTRODUCTION 

T he effectiveness of any transmitter is 
greatly dependent upon the efficiency with 
which the associated antenna system radiates 
the output power of the transmitter. Trans- 
mitters used for jamming never have so great 
an amount of power available that any appre- 
ciable loss due to an inefficient radiating system 
can be tolerated. This is particularly true for 
radar jamming, since, as is pointed out in 
Chapter 11, the closer the target is to the 
radar, the more jamming power is required to 
screen the target effectively. 

An efficient antenna system is likewise essen- 
tial if the full capabilities of search receivers 
are to be realized. Except for direction-finding 
[DF] antennas, requirements are not so strin- 
gent, however, as for transmitters. Neverthe- 
less, good reception requires an antenna system 
that is designed for the particular application. 
This is especially the case where a simple but 
not highly sensitive receiver is involved. 

Similar considerations apply to the problem 
of r-f power transmission, since the efficiency 
of the overall system depends not only on the 
antenna and the transmitter or receiver but 
also on the means used to connect the two. 

Most of the work described in this chap- 
ter on antennas and power transmission for 
radar countermeasures was done by the 
Radio Research Laboratory (under contract 
OEMsr-411). Most of the work on nonradar 
countermeasures was done by the Ohio State 
University Research Foundation (under con- 
tracts OEMsr-759 and NDCrc-100), the Radio 
Corporation of America (under contract 
OEMsr-895), and the Airborne Instruments 
Laboratory (under contract OEMsr-1305). 
The design considerations for all counter- 
measures antennas are discussed in the follow- 
ing sections ; the actual antennas developed for 
radar countermeasures and nonradar counter- 
measures are then discussed in separate sec- 
tions. This division of the discussion on actual 
antennas into nonradar and radar applications 


is made largely not for technical reasons but 
because of the fairly sharp division maintained 
within Division 15 between these two types of 
work : laboratories working on communications 
and other nonradar countermeasures (together 
with associated antennas) did but little work 
on radar countermeasures (and associated 
antennas) and vice versa. 

4 2 DESIGN CONSIDERATIONS 

Factors which must be considered in the 
design of antennas for radio countermeasures 
[RCM] include bandwidth requirements, direc- 
tional characteristics, polarization require- 
ments, and installation problems. 

Antenna Bandwidth 

Where operation is to be undertaken on a 
single frequency, or over a very narrow band 
of frequencies, the design of a transmitting 
or receiving antenna is not very difficult. Un- 
fortunately, in RCM work a wide band of 
frequencies is almost always involved. Since 
the enemy communications or radar signals 
may appear' on any frequency, it is desirable 
that each jamming transmitter have an 
antenna that will radiate efficiently over the 
entire frequency range of the transmitter. 

This is particularly desirable in airborne 
applications, where it is generally impracticable 
(except with trailing-wire antennas) to make 
any changes in the antenna while in flight and 
where it is difficult, because of aerodynamic 
considerations, to modify an existing antenna 
even at a maintenance depot. 

In practice, it is often found that the band 
of frequencies over which a transmitter is 
capable of being tuned cannot be conveniently 
covered by a single antenna structure. Under 
these circumstances the best compromise is to 
install an antenna that efficiently covers the 
known band of enemy frequencies and to re- 
place or modify this antenna if operations in a 
new band of enemy frequencies must be under- 
taken. 


54 


DESIGN CONSIDERATIONS 


55 


Practical antennas for airborne applications 
cover frequency ranges varying from as little 
as 1 per cent of the operating frequency to 
as much as two octaves in total bandwidth, 
e.g., a 200- to 800-mc antenna covers two 
octaves: one from 200 to 400 me and another 
from 400 to 800 me. Antennas for search 
receivers, on the other hand, are available for 
operation over bands in excess of 3 octaves, e.g., 
from 300 to over 2,400 me. The wider frequency 
range for receiving antennas is the result of 
less stringent impedance requirements for re- 
ceiving antennas. 

In general, as the diameter of an antenna 
increases (its length remaining fixed), the 
band of frequencies over which it is capable of 
operating increases. For this reason, all wide- 
band antennas have a relatively large cross 
section and, when intended for airborne appli- 
cations, often present mechanical design prob- 
lems, particularly as regards the method of 
mounting. Conversely, the configuration of the 
mount may greatly influence the electrical 
operating characteristics of the antenna. For 
these reasons it is important that wide-band 
antennas be installed without modification of 
their mountings or housings. 

Ground-based and ship-borne RCM installa- 
tions frequently require less bandwidth than 
airborne applications, since it is often feasible 
to make the antenna adjustable or to employ 
several antennas for a given frequency range. 

The above discussion of antenna bandwidth 
leads one to inquire just what is meant by the 
term bandwidth as applied to receiving and 
transmitting antennas. It has been found that 
most RCM transmitters will work very effi- 
ciently into a standing-wave ratio of 1.5 to 1 
or less, and that most transmitters will operate 
satisfactorily into a standing-wave ratio of 2 
to 1 or less. Receivers have been found to 
operate fairly satisfactorily into standing-wave 
ratios up to 5 to 1. 


Antenna Directional Patterns 

A very important consideration in the choice 
of an antenna or an antenna system is the 
manner in which the field strength of the 


radiated wave, or the response of a receiving 
antenna, depends upon direction. For some 
purposes it is desirable to confine the radiation 
in a very narrow beam; for others it is desir- 
able that the antenna radiate or respond equally 
in all directions. The manner in which the 
radiated energy varies with direction is indi- 
cated by means of a “radiation pattern.’’ Such 
a pattern is constructed by determining, theo- 
retically or experimentally, the field strength 
at a constant distance from the antenna in 
various directions. Points are plotted whose 
directions from a common origin are the direc- 
tions in which the radiation is measured and 
whose distances from the origin are propor- 
tional to the field strengths in these directions. 
The radiation pattern consists of the surface 
containing the points. The directional charac- 
teristics of a given antenna are, of course, the 
same for receiving as for transmitting. 

When a highly directive antenna system is 
required, a number of antenna elements may 
be used, properly spaced and excited. Such a 
system of antennas is called an “antenna 
array.” The high directivity of an antenna 
array results from the fact that the fields 
radiated by the various antennas that compose 
the array reinforce only in certain directions 
and cancel partly or totally in other directions. 
Directivity can also be increased by the use 
of reflectors, which may have a variety of 
shapes, such as a paraboloid, a V-shaped 
trough, etc. Still another type of directive 
radiator is the open end of a wave guide, 
preferably flared to form a horn. 

In using airborne jamming transmitters 
against ground communications or radar in- 
stallations, it is generally desirable for the 
airborne antenna to be nondirectional in azi- 
muth but to have downward directivity in 
elevation. An antenna of this kind will radiate 
equally well toward all ground-based stations 
regardless of their azimuth and, in addition, 
all the power will be directed downward where 
it will be of the most value. Sometimes, how- 
ever, it is desirable to have a pattern which 
has some gain in a forward direction, since 
the only stations of interest may be those ahead 
of the aircraft. 

In antennas for ground-based or ship-borne 


56 


ANTENNAS AND RADIO-FREQUENCY POWER TRANSMISSION 


transmitters, on the other hand, directivity in 
azimuth is often of considerable value. By 
using directional antennas for this application, 
not only is it possible to direct the maximum 
amount of the available po'wer toward the 
victim station, but also the possibility of inter- 
fering with one’s own channels is minimized. 

Antennas for ship-borne applications may 
require a relatively narrow beam in azimuth, 
to take advantage of the maximum gain com- 
patible with accurate directional setting, but 
may require a fairly wide coverage in elevation, 
to compensate for the roll of the ship. It is 
always necessary, for a given application, to 
consider carefully the question of whether it 
is better to use the larger amount of jamming 
power required for this larger angle in eleva- 
tion or to stabilize the antenna. 

One precaution must be observed in using a 
directional antenna with ground-based jam- 
ming transmitters that are operating against 
enemy aircraft-interception [AI] radar or 
ground-to-air communications channels of 
ground-controlled-interception [GCI] systems. 
In both of these cases, jamming signals may 
be beamed along the path that is to be taken 
by the aircraft that are to be protected. How- 
ever, if this beam is made extremely narrow 
in order to concentrate the maximum amount 
of power along the path, two adverse effects 
result. 

1. The proposed course of flight is accurately 
defined for the enemy’s benefit. 

2. While staying outside of the beam the 
enemy might conceivably be directed close 
enough to the target to permit closing by visual 
observation. 

Under these circumstances it is obviously 
prudent to sacrifice power concentration in the 
interest of not revealing one’s plans in detail. 

Broad-band directional systems in the h-f 
range present difficult antenna problems. In 
general, such antenna systems are designed as 
an integral part of the complete DF system. 
For this reason, no DF or homing antennas are 
described in this section as individual units. 
Instead, they are catalogued in Chapter 10. In 
passing, however, it should be pointed out that, 
although indications can generally be obtained 
from a DF system at frequencies outside of the 


band of operation for which the system is 
designed, these results are likely to be ambigu- 
ous. It is therefore important to use these 
systems only in the range of frequencies in 
which they are intended to operate. 


Antenna Polarization 

The radiation from simple dipoles, whips, 
and stubs is plane-polarized. In other words, 
the direction of the radiated electric field is 
parallel to the axis of the antenna. Such a 
field has maximum effect upon a receiving 
antenna when the latter is normal to the direc- 
tion of propagation and parallel to the electric 
field, and zero effect when the receiving antenna 
is normal to the field. By special antenna design 
it is also possible to produce a circularly polar- 
ized field, for which the direction of the electric 
field at any point rotates at the radiated fre- 
quency. The receiving antenna then responds 
regardless of its orientation in a plane normal 
to the direction of propagation. 

The importance of employing an antenna 
system whose plane of polarization corresponds 
to that of the enemy equipment cannot be over- 
emphasized. If the victim receiver uses a 
vertical antenna, it is important that the 
jammer antenna also be oriented in the verti- 
cal plane. If this is not done, only that com- 
ponent of the radiated power corresponding 
to the vertical component of the radiated wave 
will be effective in jamming. 

The choice between vertical and horizontal 
polarization involves more than just mounting 
a given antenna in one direction or the other. 
The questions of directivity patterns, relation 
of antenna to the ground plane, etc., are all 
involved. Consequently, it is desirable that the 
antenna system be designed for the intended 
service and that it be installed as originally 
contemplated. When the desired plane of polari- 
zation is not known or is mixed, the antenna 
may be mounted at a 45-degree angle, rather 
than either horizontally or vertically. If this is 
done, the antenna will radiate (or respond to) 
components in both planes, but with a loss in 
efficiency over that which could be obtained 


DESIGN CONSIDERATIONS 


57 


from an antenna mounted in the most favorable 
position for the wave being received. 

Antennas having shapes other than that of 
an elongated cylinder, such as cones, for ex- 
ample, generally radiate (or receive) energy in 
various planes of polarization. The exact polari- 
zation of antennas of this type is complex and 
depends upon their specific configuration, their 
relation to the ground planes, and other factors. 
The advisability of tilting antennas of this type 
can best be determined from a study of the 
actual radiation pattern of the antenna in- 
volved. 


Antenna Installation 

The mechanical design of the antenna and 
its method of installation must always be such 
that it will withstand the severe service to 
which it will probably be exposed. Since all 
antennas of the type under discussion are for 
airborne, ship-borne, ground-based, mobile, or 
portable applications, the effect of wind, tem- 
perature, ice, vibration, and shock must be 
taken into consideration. In addition, for ship- 
borne antennas the effect of salt spray must 
also be considered. These mechanical design 
requirements, when combined with the electri- 
cal ones, often produce a difficult problem. 

As a general rule, antenna installations 
should be made in such a way that, under nor- 
mal operating conditions, an unobstructed 
‘‘view’' is had of the transmitter to be observed 
or of the receiver that is to be jammed. It is 
especially important to observe this precau- 
tion at the higher frequencies used for radar 
purposes. 

In airborne applications, this requirement 
can generally be met by mounting the antenna 
on the underside of the fuselage. This location 
is not always practical, however, since the an- 
tenna may be too long for the clearance that 
exists when the airplane is on the ground. 
When warranted, retractable mounts may be 
used to overcome this handicap. As a second 
choice, the antenna may be mounted on the nose 
or on the side of the fuselage. Both of these 
locations have distinct disadvantages, however. 


In the former, the antenna is shielded towards 
the rear, in the latter, towards one side. Loca- 
tion of the antenna on top of the fuselage is 
particularly poor practice where jamming (or 
reception) of ground stations is involved, since 
the antenna is very likely to have predomi- 
nantly upward directivity; however, this does 
not necessarily apply to relatively long anten- 
nas that may be supported between the tail and 
wings of the aircraft. 

Ship-borne antennas must be installed in such 
positions that the superstructure of the vessel 
will not interfere with radiation patterns. It is 
generally necessary either to mount the an- 
tenna high enough so that no interference will 
be encountered or to mount two antennas, one 
on either side of the ship, and to use whichever 
one can be pointed in the correct direction. 

An important consideration in the installa- 
tion of any antenna is its position with respect 
to the metal surface that serves as a “ground” 
plane. Most airborne antennas are designed 
for mounting on the metal skin of an airplane 
and consequently will not perform properly if 
used without the metal ground plane. They can- 
not, for example, be located on the top of a mast 
nor can they be used on a nonmetallic airplane 
unless a metallic ground screen is provided. A 
conducting screen or netting, several wave- 
lengths in extent, should prove entirely satis- 
factory for this purpose. 

In considering the problem of providing an 
antenna that will respond to both horizontally 
and vertically polarized waves, it was suggested 
above that an antenna might be mounted at a 
45-degree angle. It is to be noted that if an 
antenna designed for mounting on a metal sur- 
face is arbitrarily tilted with respect to that 
surface, the antenna characteristics are very 
likely to be considerably altered. Therefore, 
antennas that are to be mounted at an angle 
to a metal surface must be designed with this 
in mind. In some installations, as for example 
in some armored vehicles and aircraft, advan- 
tage may be taken of the contours of the vehicle 
to mount the antenna in the proper relation to 
the metal surface while still keeping it at an 
angle to the vertical and the horizontal. The 
proper tilt and relation to the metal surface 
may be attained in aircraft by mounting the 


58 


ANTENNAS AND RADIO-FREQUENCY POWER TRANSMISSION 


antenna part way up from the bottom of the 
fuselage. Some shielding then occurs, however. 


Transmission Lines and Accessories 

The installation of many antennas is such 
that a transmission line (which may be coaxial 
line, wave guide, or other type) is required 
between the transmitter and the antenna. It is 
important that the transmission line have ade- 
quate power-handling capacity and that it be 
of the impedance value for which the associ- 
ated components have been designed. Since the 
impedance of the antenna is in general different 
from that of the line, some form of impedance- 
matching unit must be used. Although not al- 
ways evident upon casual observation, imped- 
ance-matching units are built into the bases of 
many antennas in order to match them to 
standard-impedance transmission lines. In some 
installations, however, often in connection with 
broad-band antennas, technical limitations may 
require the use of transmission lines having 
other than standard-impedance values. 


Care must be exercised in the selection and 
installation of antenna and transmission line fit- 
tings. At the very high frequencies even the 
best of these fittings introduce discontinuities 
into the circuit. Consequently only specified 
fittings can be used and no more should be 
installed than absolutely necessary. The same 
comments apply to r-f switches for these fre- 
quencies. 


ANTENNAS FOR RADAR 
COUNTERMEASURES USE 

The techniques employed in the development 
of antennas for radar countermeasures use 
have been thoroughly discussed in an RRL 
monograph,®®® so no further comment is neces- 
sary. The antennas which were carried through 
to the stage of building a prototype model, 
together with some of their characteristics, are 
shown in Table 1. A ca^logue^®® is available 
which treats each of these antennas in some 
detail, giving a complete description, discus- 
sion of operation and installation, etc. 


Table 1. Radar countermeasures antenna and transmission line developments. 


Identification 

nos. 


Description 


Frequency 
range (me) 


References 


Remarks 


Ship-Borne and Ground-Based Antennas 


RRL: F-3701 

Div. 15: RP-138 

Navy: AS-71/SPT-2 

Dipoles and 
tor. 

corner 

reflec- 

450-720* 

430 

Tunable by adjusting lengths 
of dipoles. 

RRL: F-3702 

Div. 15: RP-138 

Navy: AS-145/SPT-6 

Dipole and 
tor. 

corner 

refiec- 

625-1,250* 

818 

Tunable by adjusting lengths 
of dipoles. 

RRL: F-3903 

Div. 15: RP-138 

Dipole and 
tor. 

corner 

reflec- 

175-550* 

819 

Tunable by adjusting lengths 
of dipoles. 

RRL: F-4700 

Div. 15: RP-138 

Army /Navy: 
AS-236/APT 

Dipoles and 
tor. 

corner 

reflec- 

350-1,700* 

820 

Uses three interchangeable ad- 
justable dipoles. 

RRL: M-2906 

Div. 15: RP-138 

Navy: CAKZ-66/AKL 

Dipole with 
tor. 

corner 

reflec- 

143-275* 

708 


RRL: M-2907 

Div. 15: RP-138 

Navy: CAKZ-66/AKM 
CAPR-66/ALS 

* Standing-wave ratio 2 to 1 

Dipole with 
tor. 

l or less. 

corner 

reflec- 

265-530* 

708 



ANTENNAS FOR RADAR COUNTERMEASURES USE 


59 


Table 1. — (Continued) 


Identification 

nos. 


Description 


Frequency 
range (me) 


References 


RRL: M-2908 Dipole with corner reflec- 445-820’*' 708 

Div. 15: R P-1 38 tor. 

Navy: CAKZ-66/ALT 
CAPR-66/ALT 

RRL: M-2910 Dipole with corner reflec- 810-1,385* 708 

M-2913 tor. 

Div. 15: RP-138 
Navy: CAPR-66/ALU 

RRL: M-2926 Dipole with corner reflec- 145-310* 708 

Div. 15: RP-138 tor. 

Navy: CAPR-66/ALR 

RRL: M-1201 Dipole and reflector. 340-400* 

Div. 15: RP-138 
Navy: AS-37/SPT-4 


Remarks 


RRL: M-2924 Dipole and plane reflector. 88-174* 

Div. 15: RP-138 


Navy: CAPR-66/ALQ 



RRL: M-2901 

Div. 15: RP-138 

Navy: CAKZ-66/AJA 

Sleeve dipole and reflector. 

350-680* 

RRL: M-2902 

Div. 15: RP-138 

Navy: CAKZ-66/AJB 

Sleeve dipole and reflector. 

647-810* 

RRL: M-2903 

Div. 15: RP-138 

Navy: CAKZ-66/AJM 

Sleeve dipole and reflector. 

175-350* 

RRL: M-2904 

Div. 15: RP-138 

Navy: CAKZ-66/AJN 

Sleeve dipole and reflector. 

85-175* 

RRL: M-2909 

Div. 15: RP-138 

Navy: CAKZ-66/AJR 

Horn. 

790-1,420* 

RRL: M-2912 

Horn. 

1,375-2,440* 


M-2915 

Div. 15: RP-138 

RRL: M-2503 
M-2504 
M-2508 

Div. 15: RP-279 
Army: AS-49/TPT-1 

RRL: M-2509 Two dipoles and W reflec- 150-210* 435 For ground-based operation. 

M-2510 tor plus balun and trans- 

M-2511 former. 

Div. 15: RP-279 
Army; AS-50/TPT-1 

• Standing-wave ratio 2 to 1 or less. 


Two dipoles and W reflec- 90-150* 434 For ground-based operation, 

tor plus balun and trans- 
former. 


Dipole shortened by T loading 
element. 


60 


ANTENNAS AND RADIO-FREQUENCY POWER TRANSMISSION 


Table 1. — {Continued) 


Identification 

nos. 


Description 


Frequency 
range (me) 


References 


Remarks 


RRL: M-2414 

Div. 15: RP-138 

Double cone. 

900-3, OOOt 



RRL: M-2409 

M-2410 

Div. 15: RP-138 
Navy: CU-19/SPR-1 
AS-56/SPR-1 

Double cone plus balun. 

225-l,000t 

405, 433 

Furnishes coaxial input for 
search receivers. 

RRL: M-2406 

M-2408 

Div. 15: RP-138 
Navy: CU-19/SPR-1 
AS-56/SPR-1 

Baiun and thick dipole. 

75-300t 

432 

Furnishes coaxial input for 
search receivers. 



Airhoy'ne Antennas 



RRL: J-303 

Div. 15: RP-138 
Army/Navy: 
AS-33/APT-2 

Thick stub. 

460-775* 



RRL: M-313 

M-318 

Div. 15: RP-138 
Army/Navy: 
AT-36/APT 
AT-41/APT 
AT-52/APT 
AS-114/APT 

Thick stub. 

165-230* 

655, 443 

Available with several types of 
mounting. 

RRL: M-313 

M-318 

Div. 15: RP-138 

Army /Navy: 
AT-37/APT 
AT-42/APT 
AT-53/APT 

Thick stub. 

120-175* 

655, 443 

Available with several types of 
mounting. 

RRL: M-313 

M-318, M-801 

Div. 15: RP-138 

Army /Navy: 
AT-38/APT 
AT-43/APT 
AT-54/APT 
AS-25/APR-2 

Thick stub. 

88-130* 

70-400t 

655, 443 

Available with several types of 
mounting. 

RRL: M-907 

Div. 15: RP-138 

Army /Navy: 
AS-36/APQ-2 
AS-65/APQ-2 
AS-116/APR-3 
AS-117/APR-3 

Thin stub (cut to length). 

185-725* 


Available with several types of 
mounting. Several stubs sup- 
plied which can be cut to 
various lengths to cover var- 
ious parts of range. 

RRL: M-1203 

Div. 15: RP-138 

Army /Navy: 
AS-67/APQ-2B 

Very thick stub. 

190-2,800* 


Standing-wave ratio rises to 
2.4 to 1 in range 1,700 to 
1,850 me. Patterns above 750 
me not satisfactory for many 


applications. 


* Standing-wave ratio 2 to 1 or less, 
t Standing-wave ratio 5 to 1 or less. 


ANTENNAS FOR RADAR COUNTERMEASURES USE 


61 


Table 1. — {Continued) 


Identification 

nos. 

Description 

Frequency 
range (me) 

References 

Remarks 

RRL: M-4008 

Div. 15: RP-303 

Tapered stub with 
grounded sleeve. 

88-175* 

783 

Streamlined for high-speed air- 
craft. 

RRL: M-4011 
M-4012, M-4013, 
M-4015 

Div. 15: RP-303 

Series of tapered stubs 
with grounded sleeves. 

90-147* 

134-257* 

250-500* 

500-935* 

783 

Series of streamlined stubs for 
high-speed aircraft. Inter- 
changeable in single mount. 

RRL: M-801 

Div. 15: RP-138 
Army/Navy: 
AS-26/APR-2 

Cone. 

215-3, OOOt 
300-830* 

444, 405 


RRL: M-801 

Div. 15: RP-138 
Army/Navy : 
AS-124/APR 

Tilted cone. 

270-1, OOOt 
400-800* 



RRL: M-2101 
M-2102, M-2103 
Div. 15: RP-138 
Army/Navy: 
AT-49A/APT 
AT-49/APR-4 
AS-115/APT 

Cone. 

180-3,000t 

290-2,500* 

431, 443 

Available with several types of 
mounting. 

RRL: M-6000 

Div. 15: RP-138 

Tilted cone. 

1,000-3,5001 


Available with several types of 
mounting. 

RRL: A-2612 

Div. 15: RP-138 
Army/Navy: 
AS-44/APR-5 

Cone and high-pass filter. 

l,000-3,500t 

465 


RRL: A-2608 

Div. 15: RP-138 
Army/Navy : 
AS-125/APR 

Tilted cone and high-pass 
filter. 

l,000-3,500t 

465 


RRL: M-2807 

Div. 15: RP-303 

Two stubs plus balun. 

66-86t 


Stubs have fineness ratio 0.25 
for use on high-speed air- 
craft and are mounted tilted 
on side of plane. 

RRL: M-2803 

Div. 15: RP-303 
Army/Navy: 
CU-64/APT 

Stubs plus balun. 

95-150* 

821 

Uses pair of AT-42/APT stubs 
or pair of AT-43/APT stubs 
(for different parts of fre- 
quency range) plus balun. 

RRL: M-2804 

Div. 15: RP-303 
Army/Navy: 
CU-63/APT 

Stubs plus balun. 

150-210* 

821 

Uses pair of AT-41/APT stubs 
plus balun. 

RRL: M-3203 

M-3204 

Div. 15: RP-303 
Army/Navy: 
AS-181/AP 

Set of balanced V sleeves. 

195-675* 

474 

For horizontal polarization. 
Consists of one mount and 
three interchangeable an- 
tenna heads to cover range. 

RRL: M-3211 

Div. 15: RP-303 

U-shaped sleeve dipole. 

160-235* 


Streamlined. 


• Standing-wave ratio 2 to 1 or less, 
t Standing-wave ratio 5 to 1 or less. 


62 


ANTENNAS AND RADIO-FREQUENCY POWER TRANSMISSION 


Table 1. — {Continued) 


Identification 

nos. 

Description 

Frequency 
range (me) 

References 

Remarks 

RRL: M-3212 

Div. 15: RP-303 

U-shaped sleeve dipole. 

176-245* 


Streamlined. 

RRL: M-3301 

Div. 15: RP-303 
Army /Navy: 
AS-108/APT 

Split can. 

575-1,400* 

822 

Horizontal polarization. 

RRL: M-3302 

Div. 15: RP-303 

Split can. 

650-1,850* 


Horizontal polarization. Scaled 
model of above antenna. 

RRL: M-2202 

Div. 15: RP-303 
Army /Navy: 
AS-69/APT 
CU-42/APT 

Two crossed bent dipoles 
plus conversion unit. 

530-580* 

404 

Circular polarization. When 
fed from two separate trans- 
mitters, may be used from 
490 to 630 me. 

RRL: M-2203 

Div. 15: RP-303 

Two crossed bent sleeve di- 
poles. 

500-700t 


Circular polarization. 

RRL: M-2204 

Div. 15: RP-303 
Army /Navy: 
AS-251/AP 

Two crossed bent sleeve di- 
poles. 

440-660t 

823 

Circular polarization. 

RRL: M-2205 

Div. 15: RP-303 

Two crossed bent sleeve di- 
poles. 

310-455t 


Circular polarization. 

RRL: A-2702 

Div. 15: RP-291 
Army /Navy: 
AS-45/APR-6 

Open-end wave guide. 

3,000-6,0001 

465 


RRL: M-4902 

Div. 15: RP-303 
Army/Navy: 
AS-259/AP 

Horn. 

2,070-4,140* 

824 

Contains built-in probe for 
output monitoring. 

RRL: M-6806 

Div. 15: RP-303 

Slot. 

1,050-2,100* 

669, 760 


RRL: M-6807 

Div. 15: RP-303 
Army/Navy : 
AS-316/AP 

Slot. 

2,030-4,230* 

669, 760 


RRL: M-6808 

Div. 15: RP-303 

Slot. 

500-1,000* 

760 


RRL: M-6809 

Div. 15: RP-303 

Slot. 

395-646* 

760 


RRL: M-6811 

Div. 15: RP-303 

Slot. 

708-1,350* 

760 


RRL: M-6812 

Div. 15: RP-303 

Slot. 

1,240-2,430* 

760 


RRL: M-7302 

M-7305 

Div. 15 : RP-303 

Curved slot. 

500-l,000t 

760 

For mounting on leading edge 
of wing. 

RRL: M-7304 

M-7306 

Div. 15: RP-303 

Curved slot. 

l,000-2,000t 

760 

For mounting on leading edge 
of wing. 


* standing-wave ratio 2 to 1 or less, 
t Standing-wave ratio 5 to 1 or less. 


ANTENNAS FOR NONRADAR COUNTERMEASURES 63 



Table 1. — {Continued) 



Identification 

nos. 

Description 

Frequency 
range (me) 

References 

Remarks 


Antenna and Transmission Line Accessories 


RRL: M-2404 

Div. 15: RP-138 
Army/Navy : 
SA-14/APR-1 

12-position r-f switch. 

Up to 1,000$ 

825 


RRL: M-2415 

M-2413 

Army/Navy: 

SA-44/APR 

6-position r-f switch. 

Up to 4,000$ 

825 


RRL: M-2911 

Div. 15: RP-138 

R-f switch. 

Up to 1,700$ 


Motor-driven three-position 
switch. 

RRL: M-2914 

Div. 15: RP-138 

R-f switch. 

Up to 1,250$ 

716 

Single -pole double -throw r-f 
relay. 

RRL: R-1000 

Div. 15: RP-107 

Wave-guide Y switch. 

3,000-6,000* 

495 


RRL: M-4601 

Div. 15: RP-138 

High-pass filter. 

800 high-pass 

611 


RRL: M-4602 

Div. 15: RP-138 
RRL: Z-2905 

Z-2906 

Div. 15: RP-286 

High-pass filter. 

Band-pass filter. 

900 high-pass 

500-600 

611 


RRL: Q-1911 

Q-1912 

Div. 15: RP-442 

Band-pass filter. 

2,200-3,500 

666, 697, 
613 


RRL: Q-1911 

Q-1913 

Div. 15: RP-442 

Band-pass filter. 

2,200-4,100 

666, 697, 
613 


RRL: Q-1928 

Div. 15: RP-442 

Set of filters. 

Various bands 
in 1,000-5,000 
range. 


For use in identifying image 
and harmonic responses of 
search receivers. 

RRL: R-1000 

Div. 15: RP-107 

Variable high-pass filter. 

3,000-6,000 

664 

For use in identifying spurious 
responses in search receivers. 

RRL: Q-1902 

Q-1905 

Div. 15: RP-442 

Coaxial-line to wave-guide 
junction. 

2,400-5,300 

687 



• Standing-wave ratio 2 to 1 or less, 
t Standing-wave ratio 5 to 1 or less. 
t Standing-wave ratio 1.5 to 1 or less. 


ANTENNAS FOR NONRADAR 
COUNTERMEASURES 

A number of antennas and transmission lines 
have been developed for applications to non- 
radar countermeasures. Although the total 
number of such antennas is far less than the 
total number of the antennas developed for 
radar countermeasures purposes, there is, if 
anything, an even greater variety of types. A 
brief discussion of each general type will be 
given. 


» Developments for Ground-Based and 
Ship-Borne Equipments 

Standard antenna design can generally be 
used for communications jamming purposes, 
especially from ground-based or ship-borne 
jammers. Some work has been found necessary, 
however, in modifications of the standard de- 
signs. These are usually of a specialized nature 
concerned with the problem at hand, and their 
solution uses standard techniques; hence, no 
discussion will be given here of such problems. 
The special problems deserve mention. 


64 


ANTENNAS AND RADIO-FREQUENCY POWER TRANSMISSION 


Antenna System for AN/GRQ-1 Ground 
Jammer 

It was learned from intelligence sources, be- 
fore the V-2 rockets were actually launched, 
that they were to be provided with at least par- 
tial radio control. The AN/GRQ-1 ground jam- 
mer was available for countermeasures pur- 
poses, and it was found necessary to design 
special antennas which would cover all conceiv- 
able needs before the launchings were started. 
Eight antennas were designed for each trans- 
mitter in order to cover the frequency ranges 
20 to 35 me and 35 to 60 me in two different 
general directions and two polarizations from 
ground locations in England. The vertically 
polarized antennas were of the terminated ver- 
tical half-rhombic type, whereas those for hori- 
zontal polarization were terminated full-rhombic 
antennas. The angular coverage of each antenna 
was about 30 degrees. 

These antennas were later made portable for 
use on the European Continent. 

Radio-Frequency Switches for Model ‘Tea” 
Jamming Equipment 

A coaxial line switch^^^ (Type CLU-24314) 
was developed to provide means for selectively 
connecting a coaxial input cable to any one of a 
number of coaxial antenna feeders. This switch 
was especially designed for ship-borne use with 
the Model Tea jamming transmitter. The switch 
has very good standing-wave ratio characteris- 
tics up to 900 me and allows connection to any 
one of eight output coaxial lines, feeding an- 
tennas. 

A revised model of the switch^ss has been con- 
structed which gives satisfactory performance 
up to at least 1,500 me. 

The Wave Antenna 

An investigation^^’ ^^s made of the pos- 
sibility of using the standard Beverage-type 
wave antenna for countermeasures purposes. 
Initial tests indicated that the antenna might be 
of considerable value in the 100- to 200-kc range. 
The principal virtues of this antenna are the 
abolition of the requirement for high towers 
and the nonselective input impedance obtained. 
The principal disadvantage is that radiation in 


the direction of the conductor is obtained only 
at the cost of loss of energy in the soil.^ 

Because of the lack of efficiency involved, this 
antenna cannot be considered as a competitor 
to other directive systems consisting of arrays 
of elements having high radiation efficiency; 
however, the simplicity of such an antenna 
means that, for military purposes at least, it 
may offer worth-while advantages at frequen- 
cies up to 10 or 20 me. 

Antennas for Airborne Use 

A number of airborne antennas have been de- 
signed for nonradar countermeasures use. Most 
of the designs were in the lower-frequency 
ranges, since standard radar countermeasures 
designs could generally be used elsewhere. Some 
antennas, however, were developed for higher- 
frequency ranges, especially for uses which re- 
quired somewhat less bandwidth than provided 
by standard radar countermeasures antennas. 

V-Antennas for Horizontal Polarization 

A series of quarter-wave V-type dipoles were 
developed to give horizontal polarization with a 
reasonably uniform radiation pattern in the 
horizontal plane. A set of four antennas was de- 
veloped for the frequency range 500 to 1,500 me. 
Four more were designed for the range 1,500 to 
3,000 me. These antennas are interchangeable 
on a standard-type mounting base. 

Trailing-Wire Antennas 

The difficulty of mounting antennas on an air- 
craft fuselage for use in the upper-high-fre- 
quency and very-high-frequency bands without 
introducing serious pattern distortion caused by 
resonant and shielding effects of the nearby 
wings, tail, propeller, other antennas, etc., led 
to the development of antennas which can be 
removed from the immediate vicinity of the air- 
craft. A relatively broad-band (approximately 
20 per cent) doublet antenna was designed 
which could be trailed behind the aircraft, using 

a Radiation from this antenna (in the direction of the 
conductor) is due to refraction of the wave by the 
ground. The tilt of the electric vector depends upon the 
dielectric constant and resistivity of the ground as well 
as the frequency. There is no wave tilt over a perfect 
conductor. 


ANTENNAS FOR NONRADAR COUNTERMEASURES 


65 


a coaxial-feed cable as a tow line. When vertical 
polarization is desired, a 30-lb weight is em- 
ployed at the end of the antenna to fly at ap- 
proximately 45 degrees from the vertical. A 
small wind sock is used when horizontal polari- 
zation is desired, causing the antennas to fly 
within 10 degrees in the horizontal. This per- 
formance is for aircraft speeds of the order of 
200 mph. 

This type of antenna was investigated in the 
20- to 50-mc range, over power-handling capa- 
bilities®^ up to 3 kw. Reports have been issued 
on design details-^ and on field tests.^^-* 

Sleeve-Type Antennas 

Sleeve antennas are series-resonant antennas 
of the stub type having relatively small dimen- 
sions and impedance characteristics which, 
while not flat, are intrinsically broad-band. 
These antennas are so adjusted as to permit 
broad-band impedance matching by means of a 
simple series line-section transformer. The 
theory of such antennas is discussed else- 
where.®®® Two series of such antennas have been 
developed for nonradar countermeasures use. 
The first of these series consists of four an- 
tennas,^®* ®®* ®® which are cylindrical with the 
maximum diameter of approximately 1 in. and 
length comparable with a quarter-wavelength 
at the center frequencies of their respective 
bands. This series covers the frequency range 
200 to 850 me. These antennas are retractable 
and interchangeable in a single mounting fix- 
ture and are primarily designed for use on rela- 
tively low-speed aircraft. The second series of 
antennas consists of two antennas made of 
streamlined tubing suitable for use on aircraft 
at speeds up to about 600 mph. The antennas 
cover the bands 100 to 200 me and 190 to 450 
me, respectively, but are not easily interchange- 
able. 

Faired-in Antennas for High-Speed 
Aircraft 

Several types of relatively 1-f faired-in an- 
tennas for particular applications have been de- 


veloped where the frequency band is relatively 
narrow and where the radiation coverage is 
only over particular ranges of angle.^^®* An- 
tennas of this type are very desirable for high- 
speed aircraft, but, when a reasonably uniform 
radiation pattern is necessary, the problems in- 
volved are extremely difficult to solve, especially 
for lower radio frequencies. The slot antennas 
used widely in radar countermeasures applica- 
tions have not as yet been extended down in 
frequency range to include frequencies below 
about 100 me. It has been suggested that a 
satisfactory solution to the problem of 1-f cov- 
erage might be obtained by use of superaudible 
frequency switching between several antennas ; 
however, this has not been tried. 

Directly Fed Wing Antennas 

Some consideration has been given to the use 
of a directly fed airplane wing (i. e., a plane 
whose wing tips are isolated from the rest of 
the wing and fed directly from lines running 
out through the inboard wing section) as an 
antenna for the lower radio frequencies. Pre- 
liminary results have not been too encouraging, 
since aerodynamical considerations prohibit in- 
sulating the wing tips for large distances. This 
means that wide-band coverage is very difficult 
to achieve. 


Investigation of Hs-293 Antenna 
Directivity 

A one-third scale model of the German Hs-293 
glider bomb was constructed from information 
obtained from captured parts. A calibrated re- 
ceiver was mounted inside the missile in such 
a way that the output meter was visible from 
the exterior and the whole was mounted in nor- 
mal flight attitude on top of a wooden tower. 
Antenna patterns were obtained-^"^ in a horizon- 
tal plane for horizontally polarized waves, in a 
longitudinal vertical plane for horizontally 
polarized waves, and in a transverse vertical 
plane for horizontally polarized waves. 


Chapter 5 

TEST METHODS, TEST EQUIPMENT, AND RADIO COUNTERMEASURES 

TRAINING 


51 INTRODUCTION 

A LARGE VARIETY of test methods and equip- 
ment has been developed in connection 
with the radio countermeasures [RCM] pro- 
gram. These can be divided roughly into two 
categories : first, equipment and methods which 
were developed for use in the laboratory for the 
furtherance of research and development work, 
and, second, methods and equipment which were 
designed for the adjustment and maintenance 
of RCM facilities in the field. Because of similar 
techniques involved, the related topic of RCM 
training is discussed in this chapter. 

The majority of the work on test methods 
and equipment was done by the Radio Research 
Laboratory [RRL] under contract OEMsr-411 ; 
other important parts of the work were done by 
the General Electric Company under contract 
OEMsr-931, the Airborne Instruments Labora- 
tory under contract OEMsr-1305, the Columbia 
Broadcasting System under contract OEMsr- 
867, and the General Radio Company under 
several contract numbers, especially OEMsr- 
1005 and OEMsr-923. 


5 2 LABORATORY METHODS AND TEST 
EQUIPMENT 

A considerable number of new techniques and 
devices were developed for laboratory use in 
connection with the research and development 
program of Division 15. This is not surprising, 
in view of the fact that the RCM investigations 
made covered practically the entire usable fre- 
quency spectrum, involved measurements of 
virtually all types (power, frequency, band- 
width, etc.), and frequently made use of ex- 
tremely wide-band techniques. 

Most of the important laboratory methods 
developed by the Radio Research Laboratory 
are discussed in a monograph;®®® the RRL de- 
veloped methods which are not covered therein. 


together with laboratory test methods and 
equipment developed by the remainder of Divi- 
sion 15, are discussed in the following section. 

Test Equipment for Communications 
Receiver Vulnerability Studies 

The General Radio Company (under contract 
OEMsr-1005) undertook a development pro- 
gram to provide Jansky and Bailey (under con- 
tract OEMsr-1024) with various laboratory 
equipment needed for their work contract cov- 
ering tests of the vulnerability of a-m and f-m 
communications receivers to various types of 
jamming (see Chapter 9). In order to simulate 
the various possible interfering signals it was 
necessary to provide signal generators capable 
of pulse modulation and of simultaneous fre- 
quency and amplitude modulation. The essen- 
tial carrier-frequency range was from 20 to 156 
me, although some equipment was required to 
test lower-frequency a-m receivers. A suitable 
noise generator for noise modulation was also 
required. 

The aim of the work was to provide relatively 
small numbers of the instruments developed. 
Also, it was important that the development 
program tie in as closely as possible with Jansky 
and Bailey’s test program to provide generators 
for any particular frequency range when 
needed. Hence, the development schedule of this 
contract was planned in close cooperation with 
Jansky and Bailey. The experience of the Radio 
Research Laboratory at Harvard University 
and of the General Electric Company on radar 
jamming and frequency modulation, respec- 
tively, were made available to the General Radio 
engineers for this contract. 

To test a communications receiver for vulner- 
ability to jamming, two signal generators are 
necessary. One, which may be of a more or less 
conventional type, provides the desired signal. 
The second provides the jamming signal, which 


66 


LABORATORY METHODS AND TEST EQUIPMENT 


67 


may be simultaneously amplitude- and fre- 
quency-modulated or pulsed. Since many of the 
receivers tested were f-m receivers and operated 
in a region where no standard f-m signal gen- 
erators were available, two special generators 
were required for some of the tests. 

Signal Generator, Type P-519 

The first instrument developed was the Type 
P-519 signal generator, capable of amplitude 
modulation, frequency modulation, and pulsing, 
and covering the carrier range from 20 to 40 me. 
Four of these units were constructed and deliv- 
ered to Jansky and Bailey. These generators are 
of the beat-frequency type, in which the output 
frequency is varied by changing the tuning of 
one of the beating oscillators. Frequency modu- 
lation is obtained by a Miller-type reactance 
tube attached to the fixed oscillator circuit. Am- 
plitude modulation and pulsing are applied to 
the mixer. A capacitance-type output attenu- 
ator was used. 

Frequency Modulator, Type P-550 

The second project, carried out simultane- 
ously, involved the development of a reactance- 
tube modulator to be used with the General Radio 
Type 605-B standard signal generator over the 
carrier range between 1 and 20 me. This pro- 
vided satisfactory f-m signals for determining 
the effects of f-m interference on a-m receivers 
operating in this range. The instrument was 
known as the Type P-550 frequency modulator. 
A General Radio Type 605-B signal generator 
was also supplied to Jansky and Bailey for use 
with the modulator. This generator was spe- 
cially modified to be capable of pulsing, and a 
Type 869-A pulse generator was supplied for 
this purpose. 

Noise Generator, Type P-551 

The third project involved the development 
of an audio-frequency noise source covering the 
range from 20 c to 20 kc, with a substantially 
constant noise output. The various noise gen- 
erators developed in other laboratories were 
studied, and, on the basis of experience with 
these units, it was decided to use resistance 
noise to obtain the most even distribution of 


noise components in the spectrum. The amount 
of amplification required, however, made a 
straight 1-f circuit unsuitable because of hum 
and microphonic difficulties, and a heterodyne 
system was used. In the resulting instrument, 
the P-551 noise generator, the noise is gen- 
erated in a band at approximately 500 kc and 
heterodyned down to the audio-frequency range. 
The result is an extremely smooth amplitude- 
frequency characteristic. The instrument also 
includes both peak and rms voltmeters, and 
clipping circuits for adjusting the ratio of rms 
to peak voltage. The output power of the noise 
generator is sufficient for modulating the Type 
P-519 and other signal generators. The unit can 
also be used as a straight modulating amplifier 
for the Type P-519 generator when the latter is 
used with modulation sources of low power out- 
put. 

Signal Generator, Type P-552 

In the meantime, a fourth instrument, the 
Type P-552 signal generator, had been planned. 
This instrument was a more ambitious under- 
taking, since it was desired in this one unit to 
cover the entire carrier range from 20 to 156 
me in a single beat-frequency type signal gen- 
erator. 

One complete model of the Type P-552 signal 
generator was assembled, and parts have been 
made for three more. The project has been 
turned over to the Signal Corps for further de- 
velopmental work. The generator consists es- 
sentially of two butterfly-type h-f oscillators 
operating at approximately 600 me. Each is of 
the push-pull type utilizing two GLr446 light- 
house tubes, an arrangement which has been 
found to produce an unusually high degree of 
constancy of output Voltage as the tuning is 
varied. One oscillator is variable over a range 
of 156 me to provide the main tuning control. 
The other oscillator is variable over a narrow 
frequency range to allow for setting of the 
calibration and to provide an incremental fre- 
quency control for running selectivity curves. 
So far as possible, both oscillators are made 
exactly alike to provide a high degree of sta- 
bility in the output frequency, which is the 
difference frequency between the two oscilla- 
tors. A GL-446 lighthouse-type tube is used as 


68 


TEST METHODS, TEST EQUIPMENT, AND RCM TRAINING 


the mixer-detector and operates into a broad- 
band tuned amplifier. This in turn feeds through 
a constant-impedance, variable-capacitance type 
of volume control into a resistance-type at- 
tenuator. This combination provides constant 
output impedance at all frequencies and smooth 
adjustment of the output voltage from the 
minimum value up to the full capability of the 
instrument. Frequency modulation is applied 
to the fixed oscillator, and amplitude modulation 
and pulsing to the detector-mixer. 

Signal Generator, Type P-553 

Still another design was the Type P-553 sig- 
nal generator, which covered the carrier range 
from 100 to 156 me. This was of the master 
oscillator, tuned amplifier type with a Miller- 
type reactance-tube modulator operating di- 
rectly on the oscillator. Amplitude modulation 
and pulsing were applied to the amplifying 
stage. 

The signal generator development program 
was interrupted for the construction of the 
Type P-554 frequency multiplier, to cover 
the frequency range from 40 to 160 me. 
In order to obtain a satisfactory test signal 
with a minimum of development time, this unit 
was built as a frequency multiplier rather than 
as a complete signal generator, and it was in- 
tended to be used in conjunction with a Type 
P-519 signal generator. The frequency multi- 
plier doubles or quadruples the frequency of an 
f-m signal from the Type P-519. Provision for 
amplitude modulation is included in the fre- 
quency multiplier. 

With the completion of the Type P-554 fre- 
quency multiplier, the entire frequency range 
planned for this contract had been covered with 
equipment suitable for the antijamming [AJ] 
tests. However, the tentative specifications for 
the Type P-552 signal generator, covering in 
one unit the frequency range from 20 to 156 me, 
made this instrument seem unusually attractive 
as a general-purpose signal generator for use 
by the Armed Services and other government 
laboratories for many types of receiver testing. 
It was decided to continue this project to com- 
pletion, since no such signal generator was 
available. 

In all the equipment developed on this proj- 


ect, simplicity of control has been considered of 
paramount importance, so that a large number 
of tests can be run quickly and easily. Hence, 
all controls are direct reading. Output voltages 
and modulation percentages are indicated con- 
tinuously and directly on panel meters, and 
trimmer or balancing adjustments have been 
kept to a minimum. 

Miscellaneous Developments 

In addition to the various special instruments 
developed for this contract, modifications of 
several standard instruments were also supplied 
to Jansky and Bailey. These included one Gen- 
eral Radio Type 804-B signal generator, two 
Type 805-A signal generators, one of which was 
modified for pulsing, two additional Type 869-A 
pulse generators and various attenuators, re- 
sistors, etc., to allow Jansky and Bailey to con- 
struct the various coupling circuits required for 
connecting the generators to the receivers under 
test. 


^ Spectrum Analyzers 

Spectrum analyzers, preferably panoramic, 
are essential for many phases of RCM research 
and development, especially for the study of 
the behavior of oscillators under wide-band 
modulation. Two basic types of spectrum ana- 
lyzers were developed by Division 15 contrac- 
tors. One of these types provided a means 
(through a double-oscillator system) for obtain- 
ing frequency modulation of the local oscillator 
in the spectrum analyzer, which was essentially 
a superheterodyne receiver. Another type of 
spectrum analyzer consisted of a superhetero- 
dyne receiver with an extremely wide-band i-f 
amplifier. This wide-band i-f amplifier was used 
to feed a signal into a narrow-band sweeping 
receiver covering its entire bandwidth. 

Spectrum Analyzer, 100 to 1,400 mc. 

Type OCC 

Since no wide-range spectrum analyzers were 
available at the beginning of the magnetron 
program (see Chapter 3), a spectrum analyzer 
project was set up at the General Electric Com- 
pany (under contract OEMsr-931) and a 


LABORATORY METHODS AND TEST EQUIPMENT 


69 


variety of techniques have been evolved for 
presentation of wide spectra in the range 100 
to 1,400 me, within which most of the low- 
power magnetrons are operated. 

One spectrum analyzer design'34. m which 
has proved useful included as its basic com- 
ponent a superheterodyne receiver whose local 
oscillator is tunable over a wide range and can, 
at the same time, be swept over a narrower 
range at a 60-c rate. Attempts to sweep the 


gram in Figure 1. The incoming signal to be 
analyzed is mixed with the signals from two 
723-A/B's in a crystal which serves as a triple 
mixer. It then enters a 50-mc i-f channel about 
1 me wide. After two stages of amplification, 
it is converted to 4 me and passes through one 
narrow-band (50 kc wide) stage. This stage 
defines the overall resolution of the device. For 
60-c sweeping over a 50-mc range, 50 kc is the 
minimum bandwidth consistent with adequate 



narrow range mechanically were abandoned at 
an early stage, and the final design employs the 
beat between two 723-A/B X-band reflex klys- 
trons as a local oscillator signal. One of these 
tubes is tuned over some 1,400 me around its 
operating frequency. This requirement is not 
unduly severe since the operating frequency is 
of the order of 9,000 me. The narrow sweep is 
obtained by varying the voltage on the reflector 
of the other 723-A/B. In this way a 60-c fre- 
quency modulation of the order of 50 me is 
achieved. 

The complete analyzer is shown in block dia- 


amplitude response of the system. Finally, the 
signal is detected and amplified in a video am- 
plifier in which particular attention has been 
paid to avoiding effects due to overloading from 
strong signals and to the 1-f response which is 
extended below 50 c. Neglect of these factors 
results in a distorted picture on the panoramic 
presentation. The video signal is applied to the 
vertical plates of a 5-in. oscilloscope whose sweep 
is synchronized with the voltage which provides 
the frequency sweep on the local oscillator. 

This equipment has been built in small lots 
in two versions. The first, or RP-SJf? analyzer, 


70 


TEST METHODS, TEST EQUIPMENT, AND RCM TRAINING 


is in a cabinet rack roughly 20x22x15 in. and 
weighs 135 lb. The second and final model is 
known as the OCC analyzer. It is about 16x16x18 
in. and weighs about 125 lb. It meets Navy 
specifications and has been in limited produc- 
tion. 

The sensitivity of this analyzer is such that 


signal appears twice as the instrument is 
tuned, at two points 100 me apart (since the 
first intermediate frequency is 50 me). Several 
other spurious images and harmonics appear 
at reduced intensity. 

The spurious signals would be exceedingly 
troublesome if this instrument were to be used 



Figure 2. Block diagram of 10- to 3,500-mc spectrum analyzer. 


a 100-^v signal will appear on the screen at 
about twice the noise level. 

This analyzer can be calibrated in mega- 
cycles per inch of sweep on the face of the 
oscilloscope. Its absolute frequency calibration 
is approximate, since the absolute frequency 
of operation of the 723-A/B's is dependent 
to some extent on operating parameters. The 
input attenuator has been calibrated at one 
frequency but is slightly frequency dependent. 
No attempt has been made at image suppres- 
sion in this instrument. As a result, a given 


as a search receiver. As a laboratory instru- 
ment for spectrum analysis, used in conjunc- 
tion with a calibrated signal generator, it has 
been quite useful. 

Spectrum Analyzer, 10 to 3,500 mc 

The Type OCC spectrum analyzer described 
above has three important drawbacks. 

1. The main image and a number of spurious 
responses are present. 

2. There is no accurate calibration of fre- 
quency. 





LABORATORY METHODS AND TEST EQUIPMENT 


71 


3. The sweep frequency is not variable but 
is fixed at 60 c. 

Another analyzer was designed and built, in 
which these undesirable features are minimized 
or eliminated. At the same time, the frequency 
range covered was extended considerably. 

This analyzer^^® is also the double-super- 
heterodyne type, but the intermediate frequen- 
cies are 22,000 and 115 me instead of 50 and 
4 me. The circuits involved are shown in block 
diagram in Figure 2. The first local oscillator 
tunes from 22,010 to 25,500 me so that the 
first crystal is really a modulator rather than 
a mixer.^^® The second local oscillator (a 
2K33 “Oxford tube’O runs at a fixed frequency 
of 21,885 me and is held at this frequency by 
an AFC system. The first i-f channel at 22,000 
me consists of a tuned cavity. Suitable filters 
reject images and spurious responses. 

The overall bandwidth of the system is de- 
fined by the 115-mc i-f channel which passes 
a band 200 kc wide. This amplifier is discussed 
in more detail later. 

It will be clear from inspection of the block 
diagram in Figure 2 that images and spurious 
responses will undergo high attenuation. In 
practice it has been found possible to keep these 
signals down by at least 30 db. On signals 
strong enough to produce spurious responses, 
the amplifier design is such that limiting action 
occurs which gives warning of their presence. 

The first local oscillator is a Z-668 reflex 
klystron. It is mechanically tunable over the 
required range and can be frequency-modulated 
over 60 to 80 me by sweeping the reflector 
voltage. All but 30 me of this range is com- 
pressed near the ends of the active range, but 
expansion of the various regions of the range 
is possible. 

The frequency of the sweep is normally 60 c 
but can be varied if desired. 

The sensitivity of this analyzer is such that 
a 100-pv signal applied across 50 ohms appears 
at twice the noise level. 

Over the frequency range 500 to 3,500 me, 
an accurate frequency marker permits absolute 
frequency determination within 5 me. This 
marker is generated in a spark-excited, tunable, 
calibrated resonant line which is similar in 
construction to a standard coaxial wavemeter. 


Production of this analyzer was held up 
indefinitely by the lack of a procurement pro- 
gram on the Z-668 first local oscillator, which, 
apparently, has no other applications than this 
one. This situation has necessitated the evolu- 
tion of compromise designs using standard 
tubes and discussed in the next section. 

Other Spectrum Analyzer Considerations 
(Sweeping Local Oscillator Type) 

Many modifications of the above designs and 
incidental studies to improve them have been 
made. A wide-range spectrum analyzer^^-* 
similar to the analyzer described above has 
been developed. Several important changes 
have been made to permit the use of commer- 
cially available thermally tuned K-band tubes 
and to improve the overall performance of the 
analyzer. These changes are as follows. 

1. The first local oscillator is a Western 
Electric Type 1462 tube (which is a develop- 
mental Type 2K50) tunable over the range 
24,600 to 21,600 me. 

2. The first transmission filter is set at 
24,600 me to match the 1462 range and is 
double-tuned to give a wider band and minimize 
the stability difficulties experienced with ther- 
mally tuned tubes. The double-tuned circuit 
shows materially improved off -band rejection. 

3. The improved selectivity of the first trans- 
mission filter made it possible to eliminate the 
image- and noise-rejection filter. 

4. The second local oscillator is a 2K50 tube 
and is held on frequency by an AFC circuit. 

5. The frequency marker is a K-band wave- 
meter inserted in the wave guide adjacent to 
the first local oscillator. With this marker it is 
possible to calibrate the analyzer over the whole 
10- to 3,000-mc range. 

This analyzer has been in limited production. 

Narrow-Band Amplifier, 115-mc. One of the 
spectrum analyzers described above uses a 
second i-f channel 200 kc wide at 115 me. This 
channel was required to be logarithmic in re- 
sponse over a range of 35 db and to saturate 
at the upper limit of this range. 

The narrow bandwidth has been achieved 
by using capacity-loaded coaxial lines as reso- 
nant circuits. Used in the grid circuits of the 
amplifier, these resonant circuits achieve a 


72 


TEST METHODS, TEST EQUIPMENT, AND RCM TRAINING 


Q of 300, so that with seven stages of amplifi- 
cation the narrow bandwidth is easily obtained. 
A very close approach to a logarithmic response 
is achieved by operating in the correct region 
of the characteristic of 6AK5 pentodes. 

A photograph of the amplifier strip which 
also includes a second detector and video 
amplifier is given in Figure 3. 

A variable input impedance has been in- 
corporated in this amplifier by the introduction 
into the input circuit of a three-plate condenser, 
with two fixed plates in the grid circuit of the 
input tube and a movable intermediate plate 
to which the input is connected. 


Studies on Crystals. The spectrum analyzers 
described above employ the heterodyne prin- 
ciple in an abnormal fashion, in that the inter- 
mediate frequency is close to that of the local 
oscillator and the input signal frequency is low 
compared with both. The crystal mixer is thus 
used as a modulator, rather than as a con- 
verter.i^^ The crystal mixer plus local oscillator 
system has frequently been treated theo- 
retically as a four-terminal network with an 
h-f output, that is, with the normal heterodyne 
connections. The reciprocity theorem allows the 
results to be used for a system in which input 
and output are interchanged. In mixer systems 



Figure 3. 115-mc center frequency narrow-band amplifier. 


It has been demonstrated that the bandwidth 
of this amplifier can be made as small as 50 
kc by introduction of regeneration. 

Impedance Bridge 115-mc. To permit im- 
pedance measurements in connection with the 
115-mc narrow-band amplifier described above, 
a Schering impedance bridge®^^- was con- 
structed. Particular attention was paid to the 
physical size and component arrangement for 
this bridge, so that it was possible to avoid 
the use of two compensating components. 

This impedance bridge is used to measure 
impedances from 50 to 500 ohms. The accuracy 
of these measurements is adequate to make the 
bridge a useful tool in the design of amplifiers 
for this frequency range. 


employing silicon crystals, deductions from the 
reciprocity theorem are borne out by experi- 
ment. If germanium crystals are used, however, 
the theorem appears to break down. German- 
ium crystals have several desirable properties 
when used as modulators — in particular, very 
low conversion losses are attainable. To clarify 
this situation, a program was initiated to in- 
vestigate the four-terminal network in which 
the germanium crystal is used as a modulator. 

The reciprocity theorem has been shown to 
be totally unreliable in the case of germanium 
crystals.^^^’ In some cases the theorem fails 
to predict the improved behavior of germanium 
as a modulator, and in others germanium crys- 
tals are less satisfactory as modulators than the 





LABORATORY METHODS AND TEST EQUIPMENT 


73 


theorem would predict. The theoretical impli- 
cations of this work were not fully understood. 

Wide-Band Intermediate-Frequency 
Spectrum Analyzers, TS-54/AP 

A portable instrument covering the fre- 
quency range 80 to 1,000 me, which is suitable 
for either laboratory or field use, has been 
developed by Radio Research Laboratory (under 
contract OEMsr-411). This spectrum an- 
alyzer^^^*®®-' has been produced in reasonable 
quantities and was rather widely used, both for 


heterodyne process to related components lying 
in the 20-mc band between 20 and 40 me. Input 
signals below 500 me heterodyne with the 
fundamental frequency of the first oscillator 
to produce the aforesaid conversion, and those 
above 500 me heterodyne with the second har- 
monic of the oscillator. 

The difference-frequency components at the 
output of the crystal mixer are fed to an i-f 
amplifier which has a substantially constant 
gain between 20 and 40 me. The output of this 
amplifier is fed to a second (vacuum tube) 


A V c 



I I 


LEFT HAND PANEL 
UNIT NO. 3 

Figure 4. Block diagram of 70- to 1,000-mc spectrum analyzer. 


laboratory and field applications. It is especially 
useful in the field for determining the barrage 
spectrum furnished by a number of jamming 
transmitters set for adjacent channels. 

The techniques of the oscillator design, mixer 
design, etc., which were used in this spectrum 
analyzer have been discussed elsewhere.®^® A 
block diagram of the unit is shown in Figure 
4. The principle of operation is as follows. 

By means of a tunable oscillator, hereinafter 
referred to as the first oscillator, and an un- 
tuned crystal mixer, all input signal com- 
ponents within any 20-mc band situated in the 
range 70 to 1,000 me are converted by the 


mixer, where another heterodyning process is 
accomplished with the aid of a second oscillator 
tunable from 20 to 40 me. The related differ- 
ence-frequency components resulting from this 
second conversion are amplified by a video 
amplifier which amplifies uniformly all fre- 
quency components contained in a 100-kc por- 
tion of the i-f pass band (this is the ‘‘resolving 
power’' of the instrument). Since the ampli- 
tudes of the components in the i-f amplifier are 
also proportional to those of the input signal 
components and the output of the video ampli- 
fier is proportional to the components present 
in the i-f amplifier, the output of the video 


74 


TEST METHODS, TEST EQUIPMENT, AND RCM TRAINING 


amplifier is a function of the signal input con- 
tained in any desired 100-kc portion of the 
input signal. The location of this 100-kc portion 
with respect to the input signal band is 
dependent upon the setting of the first and 
second oscillators. The first oscillator is manu- 
ally tuned and the second oscillator can be 
tuned manually or automatically driven by a 
motor, which makes possible the visible presen- 

POWER 2N0 OSCILLATOR FIRST OSCILUTOR 

MEASUREMENT 30 MC 




SAW-TOOTH SWEEP VOLTAGE 
B 



BLANKING VOLTAGE 
C 

Figure 5. Diagram illustrating the operation of 
the 70- to 1,000-mc spectrum analyzer. For an ex- 
planation of the figure, see text. 

tation of the spectrum of a signal on the 
oscilloscope screen. The output of the video 
amplifier can be applied to a bolometer measur- 
ing circuit or to the vertical deflecting plates 
of the cathode-ray tube. 

The double-conversion (two mixers) system, 
described in the function of the spectrum 
analyzer, yields both a wide-tuning range and 
an analyzing bandwidth (100-kc resolving 
power) which are constant and independent 
of the frequency of the signal. 

A graphical representation of the function- 
ing of the spectrum analyzer can be reviewed 
by reference to Figure 5. In this example, the 
spectrum to be analyzed is located between 


290 and 310 me. The first oscillator, tuned to 
330 me, heterodynes with the components in 
the band 290 to 310 me to produce difference- 
frequency components between 20 and 40 me. 
The second oscillator, tuned to 30 me, then 
heterodynes with the latter components and 
likewise produces difference-frequency compo- 
nents; those whose frequencies are less than 
50 kc are amplified by the video amplifier. Thus, 
the output of the video amplifier is proportional 
to the components of the original input lying 
between 299.95 and 300.05 me. When the fre- 
quency of the second oscillator is varied by 
hand, it is possible to move the 100-kc band 
so as to explore the entire spectrum in the 
intermediate frequency between 20 and 40 me, 
and, consequently, the spectrum between 290 
and 310 me, because of the proportionality 
previously mentioned. It should also be noted 
that frequency components between 350 and 
370 me can also beat with the first oscillator 
to produce the i-f frequency used in the ex- 
ample. This image response should not be dis- 
regarded in the use of the analyzer. 

The power output of the video amplifier is 
determined by a bolometer-bridge circuit 
coupled to a vacuum-tube voltmeter which is 
calibrated to obtain decibel readings of power 
distribution with frequency. 

If the second oscillator is motor-driven, so 
as to cyclicly sweep over the 20- to 40-mc or 
the 27.5- to 32.5-mc range, the proportional 
voltage amplitude corresponding to all com- 
ponent signals between 290 and 310 me or 
297.5 and 302.5 me can be delineated as a 
function of frequency on an oscilloscope. This 
feature has been made a part of the spectrum 
analyzer by the inclusion of a calibrated, 2-in. 
cathode-ray tube. Provisions for connecting an 
external cathode-ray oscilloscope are included. 


5.2.3 Miscellaneous Laboratory Test 
Methods and Equipment 

A number of relatively unrelated miscellan- 
eous developments were undertaken by several 
Division 15 contractors. Several of the devices 
produced are described below, and a consider- 


TEST EQUIPMENT FOR FIELD USE 


75 


ably larger number of them are described in 
the accompanying monograph.®®^ 

High-Frequency Calorimetric Wattmeter 

Chapter 3 described the development of mag- 
netrons operating in the 100- to 1,600-mc range. 
At the time this development program was 
initiated, no simple techniques were available 
for speedy measurement of power over wide 
frequency ranges at these frequencies. It was 
necessary, therefore, to develop such tech- 
niques. 

The first wattmeters tested were sections of 
lossy coaxial line, usually at least 30 ft long, 
which were cooled by water flowing in the 
annular space between the outside of the line 
and a coaxial external copper tube. Measure- 
ments of entrance and exit water temperatures 
and rates of water flow gave reliable measure- 
ments of power dissipated, but the system 
required several minutes to come to equilibrium 
and end reflections caused difficulties at low 
frequencies, even for 50 ft or more of line. 

The power-measuring load consists of a short 
glass tube, usually an inch or two long, con- 
nected across the oscillator tank circuit at the 
point at which an external load would normally 
be attached. Through this load flows salt water 
whose salinity is adjusted until the resistance 
from end to end of the glass tube is equal 
to the normal resistive load — usually 50 ohms. 
The ends of the tube are sealed to short Fernico 
sections which are clamped to the appropriate 
points on the oscillator tank circuit. The salt 
water is pumped through a heat exchanger 
where it is cooled by tap water. The power 
dissipated in the salt water follows, as before, 
from measurements of entrance and exit 
temperatures of the salt water and of the rate 
of salt-water flow. This system comes to 
equilibrium in a few seconds. It has proved 
equally satisfactory at all frequencies up to at 
least 2,000 me and has been operated at power 
levels up to over 2 kw. 

Coaxial versions of this load have been 
designed for terminations for coaxial lines. 

Miscellaneous Items 

A very considerable number of miscellaneous 
items of more or less conventional design were 


required in the research and development pro- 
gram. These included instruments of virtually 
every type. Many of these are described in the 
chapters of this volume or of the accompanying 
monograph^^^^ dealing with the developments in 
connection with which the items were used. 
Speciflcally, these developments included syn- 
thetic radar sets, copies of enemy radar sets, 
various types of noise-analyzing equipment, 
wattmeters, crystal voltmeters, wide-band oscil- 
loscopes, frequency meters, special tube-test 
sets, antenna-measuring equipment, and a num- 
ber of other devices. For references to complete 
descriptions of these test equipments and 
methods, see the sections on test equipment in 
the Appendix. 


5 3 test equipment for field use 

As for all radio equipment, it is essential to 
supply adequate test equipment for the adjust- 
ment and maintenance of RCM facilities. Aside 
from the test equipment commonly used for the 
maintenance of radio apparatus, probably the 
most important item in the RCM field is an 
accurate and stable frequency meter. As has 
already been pointed out in the introductions 
to the receiver and the transmitter sections, 
this instrument is essential for accurately de- 
termining the exact operating frequencies of 
enemy communications and radar channels and 
for setting jammers to these frequencies. 

Next in importance for maintenance of 
transmitters are instruments for checking the 
power output of the transmitters and their 
modulation capabilities. In the maintenance of 
receivers, test oscillators or signal generators 
are useful for checking the performance in the 
various frequency bands. 

Test equipment needed for the maintenance 
of communications countermeasures facilities 
is, with minor exceptions, quite standard and 
required but little of the development time of 
Division 15 laboratories. In the case of radar 
countermeasures test equipment, on the other 
hand, the wide frequency coverage required in 
frequency bands hitherto unused demanded the 
development of virtually a complete line of 


76 


TEST METHODS, TEST EQUIPMENT, AND RCM TRAINING 


frequency meters, power-measuring devices, 
etc., over the range 100 to 10,000 me. 


* ^ ^ Radar Countermeasures Test 
Equipment Needs 

Accurate means for measuring frequencies 
are essential in RCM receiving and trans- 
mitting activities. In receiving activities, it is 
important to keep a careful check on the fre- 
quencies that are used by the enemy ; in trans- 
mitting, means are required for accurately 
adjusting the transmitters to those frequencies. 
The presetting of transmitter frequencies with 
sufficient accuracy for spot jamming is not gen- 
erally feasible. For barrage jamming, however, 
not only is it feasible to do this, but from a 
practical standpoint it is essential to do so. 
This point is discussed in somewhat greater 
detail in Chapter 11. 

If the same frequency meter can be used 
both for measuring the enemy frequency and 
for adjusting the jammer, the absolute accuracy 
of the meter is not too consequential. Its sta- 
bility, as a function of temperature, humidity, 
and pressure (altitude), may be very impor- 
tant, however. 

A simple but effective method of accurately 
setting spot jammers is to make use of an in- 
sensitive, narrow-band receiver which is tuned 
to the victim frequency and subsequently used 
to monitor, not only the jamming transmitter, 
but also the victim signal. This method is even 
more convenient in case the receiver used em- 
ploys panoramic presentation of a relatively 
wide frequency range. Receivers and receiver 
modifications for this type of use are described 
in Chapters 10 and 11. 

The need for equipment to measure the power 
output of transmitters on the test bench is self- 
evident and equipment suitable for this purpose 
was developed. In addition, however, it is 
prudent to check the performance of such 
transmitters after they are installed and con- 
nected to their regular antennas. This may be 
done with simple crystal probes and similar 
devices. Although checks of this kind are 
qualitative, they are very useful, since, being 
made under actual operating conditions, they 


are comprehensive and will, therefore, expose 
shortcomings of the overall system. 

The distribution of the energy in the side 
bands of a barrage jammer is often a function 
of the particular tuning adjustments that are 
used. Some transmitters are more critical than 
others in this respect. With such transmitters, 
the use of some simple means for determining 
the shape of the sideband energy-distribution 
curve is desirable. In addition to the spectrum- 
analyzing devices and the panoramic-receiving 
attachments mentioned above, which can obvi- 
ously be used for this purpose, it is often pos- 
sible to employ other relatively simple devices 
for specific applications. One device of this type 
is the so-called double-peaking amplifier- 
alignment unit, which assures proper alignment 
of a wide-band amplifier used as a part of many 
barrage jammers by adjusting the two peaks of 
the response curve of the amplifier so that they 
have the proper frequency separation. 

Sometimes the complete absence of signals in 
a certain band of frequencies (generally the 
very high ones) made it impossible to ascertain 
whether a receiver operating in this region was 
in good working condition. As may well be 
appreciated, after many hours of fruitless 
search over a band of frequencies wherein no 
signals are present doubts may exist concerning 
the functioning of the receiver. Test oscillators, 
capable of supplying a signal at the frequencies 
in question, are very useful for checking the 
performance of receivers under these circum- 
stances. 

For more careful measurements on the test 
bench and for alignment of the various tuned 
circuits in the receiver, use can be made of 
standard signal generators. Standard signal 
generators differ from test oscillators in that 
known and adjustable output voltages are avail- 
able, either unmodulated or modulated to a 
known degree by waves of various forms. 

The importance of having adequate test 
equipment available for the maintenance and 
repair of RCM facilities cannot be overempha- 
sized. The units mentioned above are only those 
which have been specifically developed for, or 
are particularly applicable to, the RCM field. 
In planning complete servicing facilities, there- 
fore, it is essential to make provision not only 


RCM TRAINING 


77 


for the various standard types of radio test and 
servicing equipment but for items demanded by 
the considerations mentioned above. 


Summary of Test Equipment 
Developments 

The Division 15 RCM test equipment de- 
velopments are summarized in Table 1. The 
bulk of these projects were undertaken by the 
Radio Research Laboratory (under contract 
OEMsr-411). Division 15 activity in this field 
was supplemented by commercially available 
test equipment in this frequency range, and 
by Service laboratory developments described 
elsewhere. The equipment represented here, 
however, comprises a very large percentage of 
the total required for the comprehensive RCM 
program and thus represents a fair solution 
to the requirements mentioned above. 

It was not found necessary to develop special 
field-type test equipment for nonradar RCM 
needs. 


RCM TRAINING 

Closely related to the subject of test equip- 
ment and methods because of similar techniques 
is the problem of providing proper aids to RCM 
training. Both the use of countermeasures and 


the defense against enemy use of counter- 
measures depend very strongly upon the skill 
of the personnel involved, so a very consider- 
able training program was undertaken by the 
Armed Services. Division 15 of NDRC partici- 
pated in this program, both by furnishing in- 
structors for early training courses and by 
developing specific equipments and aids to be 
used by the Armed Services in their training 
program. 


Training Courses 

In the early days of countermeasures de- 
velopment, the subject was so new and novel 
that it was necessary to train the Armed 
Services personnel who were going to be 
responsible for operational use of the equip- 
ment being developed at various research 
laboratories. RRL gave about fifteen 1- and 
2-week training courses to groups averaging 
thirty officers. The trained personnel thus pro- 
vided did the early operational application of 
countermeasures and also formed the nucleus 
for the later extensive program instituted by 
the Army and Navy for RCM training. 

A closely related activity of RRL was the 
preparation of sound motion pictures for train- 
ing use. These films®®® covered such subjects 
as operation of transmitters, use of direction- 
finding equipment, etc. 


Table 1. Summary of field-type test equipment. 


Identification 

Nos. 

Use 

Tuning 
range (me) 

References 

Comments 

RRL: A-1501 

Div. 15: RP-173 

Test oscillator. 

Signal sources 
1,000-3,000 507 


RRL: A-1700 

Div. 15: RP-191 

Jamming signal 
generator. 

2,400-3,700 

347 

Includes provisions for virtually all types 
of modulation. Designed for laboratory 
and field use in studying susceptibil- 
ities to jamming of radar sets, and as 
a standard signal source in this fre- 
quency range. 

RRL: A-2651 

Div. 15: RP-292 

Test oscillator. 

2,500-3,500 

349, 464 

Pulsed fixed frequency signal source, 
variable over specified tuning range by 
fairly complex adjustments. 

RRL: F-2200 

Div. 15: RP-289 
Army/Navy: 
TS-62/APQ-1 

R-f pulse genera- 
tor. 

460-600 

358 

For use as simulated radar for checking 
operation of automatic lock-on jam- 
ming transmitters. 


78 


TEST METHODS, TEST EQUIPMENT, AND RCM TRAINING 


Table 1. — {Continued) 


Identification 

Nos. 

Use 

Tuning 
range (me) 

References 

Comments 

RRL: Q-2105 

Div. 15: RP-286 

Test oscillator. 

5,000-10,000 

809 


RRL: U-800 

Div. 15: RP-306 

Microwave test 
oscillator. 

1,500-3,500 

811 


RRL: U-1100 

Div. 15: RP-476 
Army/Navy : 
TS-406/UP 

Test oscillator. 

1,000-3,500 

812 

Consists of resonant cavity using buzzer 
for excitation. 

RRL: U-1150 

Div. 15: RP-476 

Test oscillator. 

3,000-10,000 


Same as U-1100 except for type of cavity. 

RRL: U-1500 

Div. 15: RP-469 
Army/ Navy 
TS-403/U 

Standard signal 
generator. 

1,800-4,000 

769 


GR: P-523A 

RRL: U-500 

Div. 15: RP-195 
Army/Navy: 
TS-47/APR 

Test oscillator. 

40-500, har- 
monics use- 
ful to 3,000. 

448 


GR: P-525 A 

Div. 15: RP-160 
Army/Navy: 
AN/TPQ-T2 

Signal generator. 

90-270 

123 

Also useful for AJ training. 

RRL: M-3010 

Div. 15: RP-298 

Test oscillator. 

270-280 


Test oscillator for use in checking direc- 
tivity patterns of direction-finding 
equipment. 



Frequency meters 


RRL: B-2700 

Div. 15: RP-294 
Army: BC-1255A 

Heterodyne fre- 
quency meter. 

70-145 

356 

Superseded by RRL U/B-3000. 

RRL: U/B-3000 
Div. 15 : RP-245 
Army/Navy: 
TS-99/AP 

Heterodyne fre- 
quency meter. 

60-225 

359 

Harmonic operation up to 1,000 me. 

RRL: U/B-3100Y 
Div. 15: RP-293 
Army/Navy: 
TS-92/AP 

Double-peaking 
alignment de- 
vice. 

20-500 

402 

For adjusting double-peaked amplifiers 
of bandwidths 0.2-7.0 me. 

RRL: Y-700 

Div. 15: RP-293 

Double-peaking 
alignment at- 
tachment. 

20-500 

446 

Plug-in attachment for use with com- 
munications receivers tuning from 0.5- 
7.0 me, to perform same function as 
RRL U/B-3100Y. 

RRL: F-3600 

Div. 15: RP-290 
Army/Navy: 
TS-53/AP 

Transmitter test 
set. 

200-450 

400-700 


Combination frequency measuring and 
power-output measuring device for 
checking operation of transmitters. 

RRL: F-4000 

Div. 15: RP-306 

Wavemeter. 

240-450,400-700. 
Also 700- 
1,500 by har- 
monic opera- 
tion. 

813 

Coaxial wavemeter. 


RCM TRAINING 


79 




Table 1. — 

■{Continued) 


Identification 

Nos. 

Use 

Tuning 
range (me) 

References 

Comments 


Power measurements and miscellaneous 

RRL: F-2300 

Div. 15: RP-290 
Army: CV-9/APT 
Army /Navy: 
TS-157/AP 

Transmitter out- 
put indicator. 

Untuned 

629 

Crystal probe for checking transmitter 
output. Various mounting modifica- 
tions were developed. 

RRL: Z-1600 

Div. 15: RP-306 
Army/Navy: 
TS-118/AP 

Thermocouple 

wattmeter. 

Up to 1,000 

386 


RRL: H-300 

Div. 15: RP-306 

Noise analyzer. 


595 

Measuring device for studying the 
spectra of various noise sources. 

RRL: U-440 

Div. 15: RP-266 

Tube tester for 
Type 931 elec- 
tron multipliers. 


416 

Used for testing Type 931 tubes as noise 
sources. 


5.4.2 Training Equipment Development 

A number of devices especially adapted to 
use in training operators to recognize and com- 
bat jamming were developed. Still other devices 
were developed for training operators in the 
use of RCM transmitters and in the use of 
RCM direction-finding equipment. 

Radar Operator Training Aids 

It was recognized quite early that some pro- 
visions should be made for training radar 
operators to recognize and combat any jam- 
ming that they might encounter. The first 
equipment developed for this use consisted of 
modifications of then existing jamming trans- 
mitters. The so-called Carpet (450 to 720 me) 
and Rug (200 to 550 me) transmitters (see 
Section 11.3.1) were modified^’^^^ so as to provide 
sine wave and pulsed operation as well as 
noise-modulated operation. There was also 
developed a small plug-in unit^^^- for use with 
almost any radar jamming transmitter pro- 
vided with noise modulation, which served to 
remove the noise modulation from the trans- 
mitter and substitute sine wave or pulse 
modulation. These units were especially useful 
in training operators in the use of antijamming 
devices (see Chapter 13). 


A number of special signal generators were 
also developed which proved useful in operator 
training. Two of these (RRL A-1700 and GR 
P-525A) have already been mentioned in Table 
1 as standard field test equipment. Another 
similar training signal generator^^^ was de- 
veloped for the frequency range 500 to 1,000 
me, especially for use in conjunction with the 
Navy Mark IV radar. A still further develop- 
ment along this line was the TS-109/SPA 
interference generator,®^^ which was an attach- 
ment for the Mark I trainer for the Mark III 
and Mark IV radars. 

Spot- Jammer Operator Training 

The American-British Laboratory undertook 
a considerable program of training operators 
for the Eighth Air Force in spot-jamming 
technique. This activity necessitated the de- 
velopment of synthetic radar transmitters and 
mocking-up of special installations which re- 
sembled those used operationally. 

Direction-Finding Trainers 

A ground trainer to assist in training Ferret 
RCM observers the proper methods of direction 
finding (AN/APA-24 and other systems) was 
developed. A prototype model was constructed 
for the Army Air Forces. 


Chapter 6 

THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


INTRODUCTION " Basic Noise Studies 


T he origin and development of equipment 
necessary for the successful prosecution of the 
radar countermeasures program in many cases 
required considerable recourse to theory, not only 
because of the extremely varied nature of the 
problems encountered, but also because it was 
often necessary to determine the feasibility of an 
idea or project before the design and construction 
of equipment was undertaken. Then, too, once 
the apparatus had been made, it was often neces- 
sary to estimate its operational capabilities in 
different tactical situations. Theoretical studies 
of both the “basic” and the operational type 
were carried out, covering a wide range of prob- 
lems involving noise, frequency modulation, 
propagation, confusion reflectors, transformer 
design, and so forth (to name a number of the 
more important topics). A summary of the 
theoretical work carried out under the auspices 
of Division 15, along with an account of miscel- 
laneous developments, appears in this chapter. 
This work was carried out by various laboratories 
including the Radio Research Laboratory (under 
contract OEMsr-411), the Airborne Instruments 
Laboratory (under contract OEMsr-1305), and 
the Bell Telephone Laboratories (under contract 
OEMsr-966). 

6 2 STUDIES OF JAMMING SIGNALS 
Because of its importance as a limiting factor 


One of the first problems considered concerned 
the general (theoretical) shape of the output 
spectrum from a jamming transmitter broad- 
casting noise or a noise-modulated wave. To 
jam successfully one or more channels (spot or 
barrage) a complex interfering signal is required 
to obscure the radar pip on the receiver screen 
(see Chapter 13, Section 13.3.2). Noise was sug- 
gested early in the program as having the neces- 
sary characteristics. Further, a broad and 
reasonably uniform output spectrum, of sufficient 
spectral intensity, is a minimum requirement. 
Spectral breadth is needed to cover the desired 
channels, and uniformity to provide enough 
radiated energy in a particular frequency range 
to obliterate the enemy’s signal. With these 
attributes in mind, it was also suggested that 
frequency modulation by a continuous wave of 
suitable form might provide, in conjunction with 
noise, the needed breadth and uniformity. 

Noise Modulations 

A study of five different types of transmitted 
waves involving noise and continuous wave was 
accordingly undertaken. ^^5 general spectrum 

of the output when simultaneous but uncorre- 
lated frequency and amplitude modulation of a 
carrier (of frequency fc) by random noise takes 
place, along with frequency modulation by a 
sine wave of frequency /o, was determined to be 


ifm - f S J- 


I 


(1 + A{u) [cos (nwo + co)u + cos {no)o — co)u] du, (1) 


in electronic performance, a detailed study of 
noise, with special emphasis on its jamming 
properties, was undertaken in an effort to aid 
experiment along these lines and to answer a 
large number of general questions regarding the 
obscuring of the detection of radar signals by 
noise and, to a lesser extent, the obscuring of 
communications by noise. 


where frequency / is measured from carrier /„ 
Eo is the peak amplitude of (un-modulated) 
carrier, and A{u) and B(u) are even functions: 

Mu) = WaU) cos 2iTufdf, 

B{u) = Wb(/) sin^ irufdf. (2) 


80 


STUDIES OF JAMMING SIGNALS 


81 


Here II"^(/) and Wsif) are the spectra of the 
amphtude and frequency (or phase) modulating 
noises respectively, y and X are constants de- 
termined from the specific conditions of modula- 
tion, and Jn{b) is an nth-order Bessel function 
of the first kind. The quantity b is equal to 
Ao/27r, where Aq is the peak voltage of the sinu- 
soid producing the continuous-wave [c-w] fre- 
quency modulation; b is also known as the modu- 
ation index, defined as 


d = 1, di = 0, d2 = ds = — , 


, i7or 


v.. 


(6) 


The result is approximately a gaussian (or nor- 
mal) energy distribution in the practical cases 
k < 1.0, which generally is not sufficiently uni- 
form or broad for barrage jamming.^ However, 
this type of modulation has the favorable side- 
band to total energy ratio of 1:1. 


Frequency deviation A/ about a central frequency /c 
Frequency /o at which the above deviation is made 


It is found convenient to define a modulation 
index for noise, 1/k, where, in analogy to the 
quantities in 6, we may write 

Frequency departure from the 
carrier 4 for a steady (d-c) modu- 
I _ ^ lating voltage equal to the rms 

k fa~ noise voltage divided by the (3) 

upper frequency limit to the 
noise band used for modulation. 

The frequency /„ may be chosen at some suitable 
place, say the half-power point. 

Results for the five cases considered may be 
summarized as follows. 

Case I: Frequency or Phase Modulation by 
Random Noise Alone. This problem was ex- 
amined originally by the Bell Telephone Lab- 
oratories, Inc.^^^ The spectrum, obtained as a 
special case of equation (1), is 
El 


W) =# Z (-1)” 

s m = Q 


dm 


where <t>^^Kxo) = - 




(^) 


dx^ (27r)5 


(4) 


and for frequency modulation by a uniform band 
extending from 0 < / < /„, these values are 
obtained: 




KM) 

8 ! 


(5) 


For phase modulation by a uniform band ex- 
tending from 0 to fa it is equivalent to consider 
frequency modulation by noise whose spectrum 
is proportional to /% 0 < / < /«. Then the dm'^ 
of equation (4) become 


Case II: Amplitude Modulation by Noise 
Alone. Here the output spectriun is simply 

W{j) = - 0), (7) 

where is the mean-square amplitude of the carrier 
component, and 8{f—0) is a delta function with 
the property that it is infinite at / = 0 and zero 
elsewhere, according to the customary definition. 
It is possible in this method to produce a fairly 
uniform spectriun, but it is not easy to make the 
barrage wide. There is always the difficulty that 
considerable energy is retained in the carrier. 
Even with extreme clipping, which is mentioned 
later, half the energy remains in the carrier. 
(The question of the influence of chpping on the 
spectrum and other properties of noise is con- 
sidered below.) It was shown that chpping does 
not seriously impair the uniformity of the spec- 
trum, but it may give an undesirable ‘‘ceihng” 
in the osciUoscope pattern unless the receiver 
width is narrow compared to that of the barrage. 

Case III: Frequency Modulation by a Sine 
Wave. If there is no noise modulation of any 
kind, but only the frequency modulation due to 
the sine wave, the spectrum (1) reduces to 

T^(/) = -f - Z - nU) , (8) 

where now there are {2n + 1) sidebands located 
at frequencies dz7i/o about the “carrier’' fc 
(/ = 0). The modulation presents a discrete 
spectriun, which may be broad enough but un- 
fortunately is not sufficiently uniform for bar- 
rage jamming. The waveform in the receiver is 
insufficiently complex and is amphtude-limited. 

®Some curves illustrating W{f) are given in reference 
525 . 


82 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


Alone it is not satisfactory; but it may be an 
essential feature, in conjimction with various 
types of noise modulation, in providing a suc- 
cessful barrage. 

In any type of frequency modulation by a sine 
wave (or any other kind of nonrandom, periodic 
waveform such as square or sawtoothed waves), 
there are definite Hmits on the value of 6: if 6 
is too large, “holes’’ (in time, but not in fre- 
quency) will appear in the pattern on the screen, 
through which the pip will show; if 6 is too small, 
there is essentially only one carrier, the original 
one, and the characteristic features of the fre- 
quency modulation are lost. 

Case IV: Frequency or Phase Modulation by 
Noise with Frequency Modulation by a Sine Wave, 
When the noise band has the spectral shapes 
considered in Case I, we obtain for the output 
spectrum 

W{f) = Jnihf r E (-!)”■ d„ ■ 

( 9 ) 

T'his shows that about each of the sidebands 
(frequency n/o) produced by the sinusoidal fre- 
quency modulation there exists a spectral dis- 
tribution due to the noise. The superposition 
of these elementary distributions produces the 
overall spectrum, whose shape may thus be 
observed to depend noticeably on the modulation 
index b. As far as uniformity is concerned, best 
results may occur for values of b between 15 and 
25, approximately; this method may be quite 
effective, as all the energy available for jamming 
is in the sidebands. There may be, however, a 
ceding to the pattern on the screen above which 
the pip is discernible, unless the sweep rate /o is 
greater than about two or three times the re- 
ceiver bandwidth. 

Case V: Amplitude Modulation by Noise with 
Frequency Modulation by a Sine Wave. Here the 
continuous portion of the output spectrum is 

W(f) = I E JnibywAif). (10) 

It must be remembered that the complete spec- 
trum includes the carrier energies, mathemati- 
cally in the form of 8 functions superimposed on 
the sideband spectra. A broad composite spec- 
trum is the result, though not so uniform a one 


as in Case IV, since the various carriers, or 
sinusoidal frequency-modulation sidebands, pro- 
duce peaks in the otherwise uniform spectriun. 
Best results with regard to spectrum uniformity 
and avoidance of holes should be obtained for 
values of b which lie roughly in the range 15 to 
25. The ratio of sideband to total energy is 
limited at best (in the case of extreme clipping) 
to 1:2, and hence more power will be required 
for jamming than in Case IV. However, not all 
the carrier energy should be considered as wasted, 
since there is (so to speak) a carrier for every 
channel, which may in certain cases add to the 
jamming effectiveness. An effect in the other 
direction is the possibility of a ceihng, because 
of the fact that we are using amplitude-limited 
or highly clipped noise. It is estimated that 
this effect becomes quite pronounced when the 
receiver width is comparable to the barrage 
width, but for small receiver-to-barrage width 
ratios it should be neghgible. This type of 
modulation and that of Case IV seem to be the 
most promising of the five methods examined, 
in the light of the above work. Table 1 compares 


Table 1. Qualitative comparison of jamming 
modulations. 


Types of 
modulation 

Relative 

spectral 

uni- 

formity 

Relative 

spectral 

width 

Relative 

carrier 

wastage 

Relative 

overall 

desira- 

bility 

I FM or PM by 
noise 

Fair 

Fair 

None 

Fair 

II AM by noise 

Good 

Fair Considerable Fair 

III FM by sine wave 

Poor 

Good 

None 

Poor 

IV FM or PM by 
noise, with FM 
by sine wave 

Good 

Good 

None 

Good 

V AM by noise, 
with FM by sine 
wave 

Good 

Good 

Some 

Good 


the various types of modulation. Figure 1 
illustrates Cases I to IV in a qualitative manner. 

Experimental work,'’ carried out contempora- 
neously with these studies, tended to confirm 
the estimates of the theory. The addition of the 
frequency modulation by sine wave, however, was 
not so much of an improvement as had been 

‘’See Section 13.2.3, and references 551, 563, 569,573, 
578, and 584. A detailed summary of this experimental 
work from the radio countermeasures [RCM] point of 
view is given in reference 746. 


STUDIES OF JAMMING SIGNALS 


83 



Figure 1. Noise modulation spectra with sinusoidal frequency modulation. 



84 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


hoped, one difficulty being the technical problem 
of providing large frequency deviations of, say, 
two or more megacycles on either side of the 
carrier, at a sufficiently rapid rate. 

Pulsed Signals 

Not only noise in various forms was considered 
as a jamming signal, but pulses as well.^-* Such 
pulses, possibly of random height and spacing in 
time, may be used to modulate a carrier, subject 
to the condition that the intervals between 
pulses are long compared to the pulse length. 
Thus there is little overlapping, and, analytically 
speaking, the spectrum is that of a single pulse. 
The range of frequencies covered is of the order 
of magnitude of the reciprocal of the pulse length 
I time duration) ; and the more random the pulses 
in size and occurrence, the greater is the efficacy 
of the jamming, until in the limit of overlapping 
random pulses we have again an unclipped ran- 
dom noise wave. One advantage of the pulse 
system is its small carrier wastage, of the order 
of T /t, where T is the mean interval between 
pulses and r is the mean pulse length. The 


system is efficient only if rms rather than peak 
power is the limiting factor. It is clearly ex- 
ceedingly wasteful if high sporadic peak power 
is hard to obtain. The energy density of the 
pulse, except for a proportionality factor, is 
given by the square of the Fourier transform of 
the pulse, a familiar result: 

e = 2 I f I', (11) 

SO that to obtain a suitable spectral distribution 
one must tailor properly the shape of the pulse. 

Clipping of Noise 

In the first studies of jamming spectra due to 
noise, the noise itself was assumed to be “pure,’^ 
or random in the gaussian sense. In practice, 
however, there is always a certain amount of 
clipping present — the slicing off of the larger 
noise peaks. Moreover, when noise is used as a 

® A number of different pulse shapes and their cor- 
responding energy densities are illustrated on page 5 of 
reference 528. 


modulating wave, heavy clipping is necessary 
to put an appreciable amount of energy in the 
sideband relative to the carrier. In direct- 
noise amplification (DINA), similarly, clipping 
is always present to some degree. Accordingly, 
it was deemed important to examine the effects 
of clipping on the spectra of the noise output 
waves, to see to what extent clipping destroyed 
or modified the original spectrum of the noise 
and whether the (relative) loss of energy due to 
spectral change was a prohibitive factor, par- 
ticularly in barrage jamming, where (as men- 
tioned at the beginning of this section) a uniform 
and high-level output spectrum was shown to 
be a minimum requirement for success. 

With the help of the relations between the 
correlation function R{t) and the spectrum W{f), 
viz: 

W{f) = 4 i: R{t) cos cotdt; 

^co 

= J JV(f) cos cotdf, CO = 27r/, (12) 

and the expression for R(t) 

(13) 

the spectral distribution of the noise wave, X at 
time to and Y at time + t, may be determined, 
subject to the assumptions that originally the 
noise was pure. Here X^ = = 1, In equa- 

tion (13), f(X) represents the dynamic charac- 
teristic of the nonlinear device through which 
the random noise is passed; in the early studies, 
this characteristic was taken to be linear, limited 
at top and bottom, so that 

f(X) = Xfor |Z| < b, 

f(X) = b for X ^ 6, 

f(X) = - bfor X ^-b. (14) 

For extreme clipping, where the incoming wave 
is so severely limited that in the output it is 
essentially square (i.e., either “on’’ or “off”) 
the characteristic was chosen to be 

f(X) = 1, Z > 0, 

/(X) = -1, Z<0. (15) 

It was chiefly with this latter case in mind that 
the first studies^^^ were undertaken. A short 
treatment of the characteristic given by equation 
(14) was carried through, enough to complete 


^ 2H1 - rfi dY}{X)f{Y)e - - 2r.VK)/2(l - 


STUDIES OF JAMMING SIGNALS 


85 


the data for Figures 2 to 4; a more comprehen- 
sive study^^®’ is discussed below. 

From equation (15) the correlation function 
becomes 

R(t) = - sin-1 

TT 

Two cases are distinguished: (1) Dina, where 
the input noise to be clipped is confined to a 
band narrow compared with its mean frequency, 
and there is no carrier; and (2) amplitude modu- 
lation of a carrier modulated by random noise, 
the r-f part of which is then passed into the 
“clipper.” In the first case the output corre- 
lation is 

R{t) = - sin-i [ro{t) cos coj], (17) 

TT 

where ro{t) is the correlation of the noise, and 
fc is the central frequency of the noise band. 
For the second case we find 
2 

R{t) = - cos cx)ct sin-1 

TT 

where now fc may be interpreted as the carrier 
frequency. Both case (1) and case (2) were 
treated exphcitly for a uniform band of noise 
extending from —coa to +coa. The resulting 
spectra appear in the form of zones, four for the 
approximation used. We have for case (1): 


IF(/)2 = 2TrE^ = — (1.1928 - 0.05785/c2 + 1.579 • 
10-V - 1.94 • |fci <1, (20a) 

= — (0.2533 - 0.1174/c - 6.59 • 

U>a 

10-3fc2 + 7.138 • 10-V + 1.334 • 

10-<A:« - 2.035 • lO-^/c* + 1.454 • 10-»/l:»), 
1 < |fc| <3, (20b) 

= — (0.13012 - 6.820 • 10-2* + 5.5 • 

Ct)a 

10-<*2 + 6.4 • 10-V - 1.637 • 

10-2*^ + 1.63 • 10-^** - 5.814 • 10-«fc«), 
3 < 1*1 < 5, (20c) 

= — (8.02 • 10-2 + 2.950 • 10-2* - 2.875 • 

Oia 

10-2/c2 + 1.031 • 10-2/c3 - 1.832 • 

10-3/c4 + 1.63 • lO-^/b^ - 5.814 • 

5 < I A: I <7, (20d) 

where again = 0, for \k\ > 7, unless more 
terms in the original series for are employed. 
Here the expression above for W(f )2 is 18 per 
cent too small. This, however, is not too serious 


lF(/)i = 2irE^ = — (1.134 - 0.0410*2 + 9.552 • lO-^*^ - 1.060 • lO-**'), |*| < 1, (19a) 

Oia 

= — (0.1799 - 0.0890* - 1.20 • 10-’*2 + 4.51 • lO-*** + 1.26 • lO-**^ 

Ola 

- 1.113 • 10-2*2 + 7.89 • 10-2*2), 1 < |fc| < 3_ (19b) 

= — (0.0808 - 4.492 • IO- 2 * + 2.61 • 10-2*2 + 3.208 • lO-**^ - 8.809 • lO-^*^ 

Ola 

+ 8.91 • 10-2*2 - 3.18 • 10-2*2), 3 < |fc| < 5, (19e) 

= — (4.39 • 10-2 + 1.613 • 10-2* - 1.571 • 10-2*2 + 5.65 • 10-2*2 

Ola 

- 1.003 • 10-2*2 ^ g gi . 10-5J;5 _ 3 ig . 10-6*6), 5 < 1*1 <7, (19d) 


and = 0 for | A; | > 7, unless more than four 
terms of the series are used. The series (19a) 
to (19b) are in deficit from the true value by 
about 6 per cent, if attention is confined to the 
spectrum W(/)i about the first harmonic of fc. 
For case (2) the results take the form: 


an error if one is interested primarily in the 
spectral distribution for |^| ^1, corresponding 
to the width of the noise band before clipping, 
for most of the omitted energy is located outside 
the band. In other words, the percentage error 
is here least for k = 0, about 6 per cent, out to 


86 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 



















































1.00 











TYf 

’E A. 

EXT 

REMEU 

CLI 

PPED 

)INA 



.90 



UN( 

:lippi 

ED UN 

IFORM 

1 SPEC 

TRUM 












.80 



I 





































.60 




















.50 


1 

UNIFO 

RM SP 

ECTRU 

IM AFl 

ER E> 

(TREME 

E CLII 

PPING 










.40 




















.30 




















.20 




















.10 































>5.0 

.1 

4.0 

-3 

.0 

-2 

.0 


.0 

( 

) 

1 

.0 

2 

.0 

3. 

K 

0 

4. 

0 

5.0 






















= 



) 


Figure 2. Noise spectrum of Dina after extreme clipping. 































Eo, 




















1.00 











TYPE 
OF A 

B. 1 
CARR 

^MPL^ 
lER B' 

TUDE 

Y CLI 

MODUL 
PPED 1 

AT ION 
NOISE 




.90 



/ 

, UNCLIPPED UNIFORM SPECTRUM 





.80 



y 

















.70 




















.60 




















.50 




, UNII 

-ORM : 

5PECT 

CLIP 

RUM A 
PING 

FTER 

EXTRE 

ME 










.40 



7 















.30 




















.20 




















.10 































-5.0 

-4 

.0 

-3 

1.0 

>2 

t.O 

-1. 

.0 

( 

[) 

1. 

0 

2. 

0 

3. 

H 

0 

4. 

.0 

5.0 






















= 


) 


Figure 3. Spectrum of a carrier ann:)litude modulated by extremely clipped noise. 




STUDIES OF JAMMING SIGNALS 


87 


! ^ I =1, and increases for larger values of \k\. 
The spectra of equations (19) and (20) are illus- 
trated in Figures 2 to 4. Clipping at an inter- 
mediate level is also shown — see equation (14). 
This particular study also included ‘"gaussian” 
and “optical” spectra.'^ 

If the clipping is not done below the rms level 
before limiting (equivalent to clipping at about 
1.4 times the rms level after clipping), there is 


for (2) it materially diminishes the wastage of 
power in the carrier frequency. These facts are 
demonstrated for an originally uniform noise 
spectrum in Tables 2 and 3. The bottleneck 
factor in Table 2 is the spectral ordinate at 
1^1 =1 (see Figures 2 to 4) . The ratio of effec- 
tive energy to total mean energy is obtained by 
dividing the bottleneck factor by 1 + p, where 
p is the ratio of carrier to sideband energy. The 






























20)^1 

it) 




















1.00 


r 

' b = 

CO 

[UNC 

LIPPE 

D UNI 

FORM 

SPEC! 

RUM] 

TYPE 

: A. 

DINA 

CLIPI 

PED A 

T AN 

ARBIT 

RARY 


qn 



'^b = 1.0 






1 











Ltv 

tL 




80 



= 

0.5 
















[EXT 

REME 

CLIPP 

IHG] 











fin 



'^b = 

0.0 












• QU 






K = CLIPPING LEVEL 











• 50 






R 

B 

MS NO 
EFORE 

ISE 1 
CLIP 

■ EVEL 
>PING 











• hO 




















.30 




















. 20 

10 



.t>S( 

D.O 

1 


























•5.0 

-M 

.0 

-3. 

0 

-2. 

.0 


.0 

c 

1 

1 


.o 2 

.0 

3.0 

K 

4. 

.0 

5.0 






















Figure 4. Spectra of Dina after clipping at arbitrary levels. 


practically no distortion of the spectrum. Even 
in the case of extreme clipping or “superclipping” 
the wastage of power due to spoiling of the 
spectrum^s uniformity is small, amounting to 
only 31 per cent in case (1) and 24 per cent in 
case (2). Of the 31 per cent loss in (1), 19 per 
cent is due to production of bands about har- 
monics of the central frequency. Corresponding 
harmonics are absent in (2). Clipping is bene- 
ficial in either (1) or (2) from the standpoint of 
reducing peak power requirements. In addition^ 

‘^The effects of clipping on these can be observed in 
Figures 7 to 10 of reference 547. 


ratio of effective energy to peak energy is found 
by dividing the bottleneck factor by ¥/R{Qi), 

where R(Q) = h"- - + (1 @(6/V2) 

‘e~’^dy. 

Table 3 was drawn up similarly for case (2). 
The same definitions apply here as in Table 2. 
The peak power, the power in the noise side- 
bands, and the power in the carrier are propor- 
tional to 46^, R(0)y and respectively; p is then 
b^/R{0). In case (1) there is no carrier, and the 


^ r 

and © is the famihar error integral “ I 

J 0 


88 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


ratio of peak power to rms noise power is h‘^/R{0), 
instead of Ah‘^/R{0) as found for case (2). 


Table 2. Effect of clipping on Dina noise — Case (1). 



Extreme 

clipping 




No 

clipping 

Clipping amplitude ^ 
Original rms amp. 

0 

0.5 

1.0 

2.0 

OO 

Clipping amplitude 

1.00 

1.17 

1.39 

2.09 


Rms amp. after clipping 


Bottleneck factor 

0.69 

0.86 

0.95 

0.97 

1 

Fraction of the energy in 
harmonic zones 

0.19 

0.08 

0.03 

0.005 

0 

Effective energy 

Total mean energj* 

0.69 

0.86 

0.95 

0.97 

1 

Effective energj' 

Peak energy 

0.69 

0.63 

0.49 

0.22 

0 


Table 3. Effect of clipping on a noise-modulated car- 
rier — Case (2). 


Extreme No 

clipping clipping 


Clipping amplitude ^ 
Original rms amp. 

0 

0.5 

1.0 

2.0 

OO 

Clipping amplitude 

1.00 

1.17 

1.39 

2.09 


Rms amp. after clipping 


Bottleneck factor 

0.76 

0.88 

0.95 

0.98 

1 

Ratio of sideband to 
carrier energy = 1/p 

1.00 

0.74 

0.52 

0.23 

0 

Effective energ}' 

Total rms energy 

0.38 

0.37 

0.32 

0.18 

0 

Effective energy 

Peak energ}’ 

0.19 

0.16 

0.12 

0.06 

0 


It is to be observed once again that the effec- 
tiveness of clipped noise in jamming a receiver 
is not determined from a study of the spectrum 
of the transmitted wave alone. For, qualita- 
tively, if the receiver breadth is small compared 
with the noise band, the received disturbance 
will have the same type of gaussian fluctuation, 
and hence the same effectiveness, as undipped 
noise with the same spectral distribution. But 
if the receiver is comparable with the noise band 
in width, there will be a tendency, as a result of 
the chpping, for a ceiling in the resultant deflec- 
tion of the recording device, and, under these 


conditions, the utility of clipped noise for jam- 
ming is materially diminished. 

Rectification of Noise 

The first treatment^^^ of limited noise dealt 
only with symmetrical clipping by a linear 
characteristic. The study was extended to the 
more general cases of chpping due to arbitrary 
cutoff and saturation levels^®^’^^° in connection 
with the modification of the spectral output of 
various noise sources, described from this point 
of view in Section 6.2.3. The principal analytic 
results are outlined below. 

For a general input voltage V{t) entering the 
nonlinear device, the output current is given by 

I{t) (21) 

where C is a contour extending from — oo to + oo 
and is indented downward in a semicircle about 
a possible singularity at the origin. The function 
f{iz) is the Fourier transform of the detector 
characteristic and usually has a simple pole or a 
branch point at 2 : = 0. The convergence of the 
integral of equation (21) is unaltered if the 
contour is extended in the form of an infinite 
semicircle either in a counterclockwise (positive) 
or clockwise (negative) sense, depending on 
whether the coefficient of iz in the exponential is 
positive or negative, respectively. When C is 
traversed in a positive fashion, the residue at 
2 = 0 yields the output current as the desired 
function of V{t)y whereas, for the negative cir- 
cuit, lit) vanishes. In this way one is able to 
distinguish between the cutoff and transmission 
states of the apparatus. 

If the correlation function Rit) of the output 
is known, the energy spectrum is found at once.® 
Following the method suggested by Rice,^^^ we 
obtain finally the spectrum 

nx/) = z hl.„ (22) 

» =0 ” • 

where 

^ <x> 

C,.„(f) = 4 m” cos (23) 

and 

r «"/(i2)e-'^<")*^/V^. (24) 

Jc 

®See equation (12); also see page 16 of reference 547. 


STUDIES OF JAMMING SIGNALS 


89 


The expression yp{t) is the correlation function of 
the input disturbance, given by 

yp{t) = w{f) cos MJ, CO = 27r/, (25) 

where w{j) is the spectrum of the incoming wave. 
The mean-square input noise voltage ^(0) = xp is 


m = (26) 

Then the correlation function of the output 
wave is 


R{t) = i: ^4^ hi,„ Htr- (27) 

n =0 ^ I 

The d-c and continuum powers become 

Wd-c = hi,, 


W. 


~ n\ 


(28) 


n = l nl 

An alternative form for the total power output is 


We = E(0) - hlo. (29) 


Three specific dynamic characteristics were 
examined. They are illustrated in Figure 5. 


for which we obtain 

^0.0 = \c (0c - 1) - k (©6 - 

Z 6 


+ 2 (<^C — 

(31a) 

= [©c - ©6„], 

(31b) 

= /3 (-1)^+2 /2 ^l-n/2 [0^(n-2) 

- 00 (’■-3)], 7! = 2, 4, 6 • • • 

(31c) 

= (-1)^+3 /2 ^l-n/2 [0^(n-2) 

- 0o„('-»], n = 3, 5, 7 • • • 

(31d) 


where the following abbreviations are indicated: 

The functions © and are defined as 
2 

© M = — I e-y" dy, 

TT" Jo 


© 

© (Xo) = -©(-^o), 


(33) 


dx^' (27r)’ 

(ZtY 

with Hj(xo) an Hermitian polynomial of the 
yth order. The total power output is in this case 


^(0) = 5 [(c - h,y + (1 + 2Cb, 


C^©c) - (1 + hl)Qto + 46o 0. + 20,w + (34) 


Here bo is the cutoff voltage, measured from the 
operating point, and C is a voltage, measured as 
indicated in Figure 5; jS, 7 , X are tube constants 
with the dimensions of mhos. 

Linear Rectifier. For the biased and saturated 
linear rectifier, we have 


Kiz)e = 


{izf 


(30) 


Type A Quadratic Rectifier. For the biased, 
saturated type A quadratic response, illustrated 
in Figure 5, one has 



from which it follows, in conjunction with equa- 
tion (24), that 


Ko = -y^ [ (0''» “ + ^ ^ “ 2<#-c) ], (36a) 


h.i = — nY* [So (©6„ — 0c) + 2 (06, — 0c) ], (36b,) 

ho , 2 = 7 " [ ©f.. - ©c + 2(C - So) 0c ], (36c) 

ho.n = 2lV (-l)»-3/2 02--./2 [0t„(-» - 0„(n-3) - (5„ - Q 0c<»-«], « = 3, 5, 7 • • • , (36d) 

ho.n = 2t' (-1)’'-2« 02-„/2 - 0c(”-3) - {bo - C) 0c<»-^>], « = 4, 6, 8, • • • . (36e) 


90 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


For the total power output we have the closed and the spectra were determined for a variety 
expression, analogous to equation (34): of input spectra and operating conditions; i.e.. 


R{0) = 


(3 -f- 6^0 H~ K) 


(0c - 0. ) 


(5= + 5bo) <t>bo - + 3C + 6blC - iC% - 86„ - 46=) 0, J, C & bo- 


(37) 


Type B Quadratic Rectifier. For type B quad- values of and C. The theory of extreme or 
ratic detector, shown in Figure 5, we may write superclipping was also generalized for the pre- 


Q—ihQZ^Q—i{2C — ho)z 2g" 

{izf 

C a bo. (38) 


]■ 


f (iz)q_B = 2\^ 

The ho,nS in this instance have the forms 


vious work^^^ to give, for the correlation function 
of the highly chpped output, 

0 < e « 1, (43) 


fl (0 = 


bo.o — — _j_ ^( I — ?) i j (02C - bo ~ 1 ) 

+ (2C - bo) 02C -6„ - (0c - 1 ) + 24.c], (39a) 

bo.i = [bo (<dbo - 1) + 2K + (2C - bo) (©2C -6. - 1) + 202c - bo - 2C (0c - 1) - Hd (39b) 

bo .2 = X2 [06„ + 02C - bo - 20c], (39c) 

bo,„ = 2iX^ (-1)"-^ « + <l>2c - b„‘“-’> - 20c<”-«], n = 3, 5, 7, ■ • • (39d) 

bo,„ = 2X2 (-l)--^/^ ^2-»/2 + .#. 2 c -bo<”-'> - 24>„('“-2)], re = 4, 6, 8 • • • (39e) 


where the additional abbreviations 



have been made. The total output power J?(0) 
here takes the form 


ff(0) = ^ [ Pl02C - bo - T20C - P30bo 
+ 2P402C -60 + 2P5</)c — 2P606o 

+ 4(C- WM, (41) 

where now 

Pi = 16C36 o - 28C25^ + 16(765 - 365 

+ 20 C 2 - I 6 C 60 + 265 + 3, (42a) 

P 2 = 4C4 - 4(7^65 - 465 + 20(7‘^ - 16(76o, (42b) 

P 3 = 65 + 665 + 3, (42c) 

Pa = 365 - 56o + 860 C 2 - 1065(7 + 10(7, (42d) 

P 5 = 4 (46o - 4C + 65(7 - C'), (42e) 

Pe = 65 + 56o. (42f) 


Conclusions. From these general results, equa- 
tions (22) to (42f), the distributions of the power 


where B is €^7^ and 4e^X^ for the hnear type 
A and type B devices, respectively. Here r{t) = 
yp{t) /\l/{0). The total output power and that in 
the continuum are 



A few general observations are pertinent. 
(1) The output power is independent of the spec- 
tral shape of the input disturbance,^ and (2) 
chpping, whether at the “top” or “bottom” of 
the wave, always spreads the spectrum. There 
are other interesting results that are more readily 
considered in Section 6.2.3, in which specific 
application of the above analysis to the problem 
of distorting the output spectrum of various 
noise sources is given. 


^ See equation (4.9-19) of reference 835. 


STUDIES OF JAMMING SIGNALS 


91 


Visibility of Signals through Noise 

The general problem investigated in Section 
6.2.1 is concerned with the spectral character- 
istics of broadcast noise, or noise-modulated 
waves, primarily from the RCM viewpoint. A 
considerable amount of work was done also on 
the general problem of jamming effectiveness 
from a somewhat different outlook; specifically, 
on the theory of the nonlinear operation of 
various devices upon a signal in the presence of 
noise. The device in question is the second 
detector of the receiver being jammed. This 
subject has been approached with two separate 
but allied ends in view. The first, of course, is 
the eftectiveness of RCM in obliterating a signal 
viewed on the oscilloscope screen or perceived 
by other methods, and the second concerns the 


practical responses. The correlation function of 
the output of a general nonlinear device was 

shown to be^®^ 

R{t) = G {to, t'o) G (^0 + i, to + t) 

dt'o ^^R^{t'o,to;t), (45) 

j Jo -L 0 

where t'o applies to the modulation, if any, to 
the carrier, and RN{to,t'o',t) is the correlation 
function of the output after the averaging over 
the random noise variables has been performed — 
in the manner, say, of equation (13). The 
quantities Tq and T'o are the periods, respectively, 
of the carrier and modulation. If the envelope 
and carrier are uncorrelated, as they usually are, 
t'o and to are independent; however, should there 
exist correlation between envelope and carrier, 
then t'o and to would be functionally related. 

Now Rn is determined by 


Rn {toy to’,t) — J* I {X, to, t'o^dX 


I{Y , to-\-t, to-\-t)dY 

27r^ (l-r2)i 


g-(X2 + 72 _ 2rXY)l2 (1 - r2) 


(46) 


efficacy of antijamming [AJ] measures in nulli- 
fying enemy interference. It was realized early 
in the program that a study of the spectnmi of 
the transmitted wave was not enough; conse- 
quently, a general theoretical examination of a 
number of methods of detecting signals in the 
presence of noise was started in the summer 
of 1943. 


where I (X, to, to) is the output current as a 
function of input voltage at one time to, and 
I(Y, to -h t, to -j- t) is the output at time t later. 
The quantity r{t) is the correlation of the input 
noise, and xp is the mean-square input voltage. 
Let fi = /i (^0, to), fa= /^{to -Y t, to t) be the 
periodic part of the incoming signal and noise; 
then it follows at once from equation (46) specifi- 
cally for a biased, linear rectifier that 


Rn (to, t'o;t) f dX f dV 

ZTTXf/Jbo-fy Jbo-h 


(X+/i-&0)(F+/2-M 

(1 — r^)i 


-(X2 + 72 _ 2rXY)/2 r/' (1 - r2) 


(47) 


Rectification of a Modulated Signal in 
Noise 

Before it can be determined to what extent 
noise inhibits the reception of signals, a theory 
must be constructed capable of handling at least 
the more important aspects of the detection of a 
modulated signal in the presence of noise by 
(1) a linear rectifier, and (2) a quadratic rectifier, 
since these two dynamic characteristics are suf- 
ficient approximations to a large number of 


where 13, as before, is the dynamic transcpnduc- 
tance of the tube. For a modulated carrier, one 
may write 

f{t) = F{t) cos coot, coo = 27r/o, (48) 

with /o the carrier frequency and F{t) the enve- 
lope. The ‘‘discrete,’’ or slowly varying portion 
of the output may be obtained on setting t = od 
in equation (46) in so far as the more rapidly 
varying noise is concerned; the result for equa- 
tion (47) is 


Rx {to, to’, 0 discrete 


27n/' 



-/i 


dX f 

J bo —f2 


dY (X + /i - bo) (Y +fo - bo) 


= (X fl — bo) AT (1^ +/2 — bo)N- 


(49) 


92 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


Then for the biased hnear detector the mean 
area under a cycle of the carrier after rectifi- 
cation is- 


1 

area ~ TfT I (A + /i — 6o)iV dfo 

i 0 Jo 


bo - /(to) 

[X + f(to) - bo] e- ^ JX. (50) 


From equation (50) it was also shown that 
when there is no bias (bo = 0) the results of 
North, Goudsmit,^^^ and Jordan^=^* are equiva- 
lent. The expressions are 

E(0 m. area 


V^27r 


e 




X 


far- 

2<P 


2’^’ 


2^ r 


(51) 


where iFi is a confluent hypergeometric function, 
and lo and Ii are modified Bessel functions of 
the first kind. 

For small-signal quadratic rectification, Rx 
was shown to be^®® 


Rn (to, t'o', t) 

= tV (1 + 2r2 + 4a6r + + a' + 5^) 

+ (r -f ab) +0(2 + a^\pi (a + b) 

+ ay ^ (2 + a2 + 52) 

+ (a + 6) (1+ 2r + ab), (52) 

where 

_ F(to) cos c^otp 

. ' 

1 _ E(tQ -|~ t) cos coq (tp -|~ t) 


and F represents the modulation on the carrier 
cos o)ot. The quantities a, 13, and 7 are constants 
of the dynamic response, which is a general 
parabola of the form 

7(0 = a -f 13V (t) + 7F(0^ 

for all values of y(^)— this latter on the assump- 
tion that the incoming wave is small-signal; that 
is, that very large amplitudes relative to the 


®It should be noted that in reference 389 equations (10) 
and (15) to (18) are not correct; one should insert —60 
in the parenthesis (jc +/i), etc. 


transmission portion of the characteristic occur 
very infrequently. One interesting conclusion 
of the analysis^*^ is that for half-wave quadratic 



Figure 5. Dynamic characteristics of biased 
saturated linear and quadratic rectifiers. 


responses the ratio of the 1-f part of the signal 
(i. e., the envelope) to the 1-f noise (without 
signal) is the same as for full-wave rectification, 


STUDIES OF JAMMING SIGNALS 


93 


each diminished by a factor 4 from its value in 
the latter instance. 

Reception of Radar Signals through Noise 

The next effort was directed toward a theoreti- 
cal examination of the relative sensitivity of the 
perception of radar signals in the presence of 
noise by visual detection (the A scope), by 
aural detection (in which one hstens to the 
fundamental or a low harmonic of the prf), and 
by a meter. The metering scheme may be either 


Signal-to-Noise Ratios. In visual perception, 
the criterion for the detectability of a signal in- 
volves, to a first approximation, the ratio of 
peak signal to mean noise background (without 
signal), whereas in amal or meter detection the 
important ratio is that of the signal energy in 
the particular harmonic component (the constant 
or d-c component in the aperiodic meter) to the 
noise energy in the frequency region surrounding 
this component, which the audio or meter filter 
passes without appreciable attenuation. The 


^ I 

1 1 1 1 III 










VISUAL SIGNAL TO NOISE RATIO. LINEAR RECTIFIER 










VISUAL SIG 

NAL TO NO 

ISE RAT 

10, Q 

UADR 

ATK 

: RE 

:cT 

IFI 

ER 














































.973(1-. 1246a, 
































957 ( 

I-. 

15; 

260 














































lA) COMPARISON OF THE LINEAR WITH THE QUADRATIC DETECTOR 

FOR VISUAL RECEPTION, AT MATCH. 









(B) COMPARISC 
FOR AURAL RE( 

‘^o=(Sf/„ ) 

_ 

5N OF THE 

:eption, a 

LINEAR 

T MATCI 

WITH 
i, GAL 

THE 

ISSIA 

QUA! 
iN PI 

DRA' 

ULSI 

ric 

0( 

ITECTOR 









r MATCH 

















T = 1 


AUR/ 

IL SIG 

INAL 

TO 1 

gois 

IE 1 

RAT 

10. LINEAR RECTI 

IFIER 








1 db 


AURAL SIGNAL TO NOISE RATIO, QUADRATIC RECTIFIER | 

1 1 1 1 1 1 1 1 1 









.! .2 3 -H .5 .6 .7 .8.9 1.0 2 3 4 5 6 7 8 9 1C 

(To 


Figure 6. Comparison of the linear with the quadratic detector in aural and visual reception. 


aperiodic, where the rectified current is fed 
directly to a meter with a long time constant, 
or periodic, where the rectified current is sent 
through an audio filter tuned to the prf, given a 
supplementary rectification, and then passed 
through the meter. The dependence of the 
sensitivities of the different methods on various 
relevant parameters was studied in some detail. 
These parameters included the width and the 
shape of the i-f response, the pulse length, the 
prf, and, in aural or meter reception, the duration 
of the gate, the width of the audio filter, or the 
time constant of the meter. The principal 
results are outlined in the following paragraphs. 


ear is known to have the power to discriminate 
frequency, a property which is equivalent to 
smrounding the signal by a filter of a certain 
critical bandwidth. The advantage of this 
natural filtering action of the ear is that it does 
not require knowledge of the prf. 

When one listens to or looks for a signal with 
the help of one’s receiving apparatus, it is done 
against a noise background, man-made or natural, 
which tends to obscure perception. The abihty 
to detect a signal depends^®® on the magnitude 
of the ratio of the signal at the point of reception 
(i. e., on the screen, at the earphones, or on a 
meter) to the appropriate noise background. 


94 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


For visual reception involving quadratic detec- 
tion it was shown that 



(53) 


where (sv/nv) is the (peak) video signal-to-noise 
ratio perceived on the scope, and (sf/uf) is the 
ratio of the rms signal to noise, before rectifica- 
tion but after filtering by the i-f stages. For 
linear rectification equation (53) becomes 



(sri 

j ‘ = 0.957, 7 = 0,0763, k 




(54) 

1.50. 


When the signal is small in comparison with the 
rms noise, i,e,, when (sF/riFy « 1, we may 
neglect the second term in equation (54), and then 
the linear rectifier behaves almost exactly like the 
quadratic. In fact, for most practical purposes 
we may set 70 = 1, so that under these conditions 
the performance of both detectors is identical. 
For strong signals {sf/uf = 1) the quadratic 
detector becomes noticeably superior (> 2 db) 
to the hnear one, as shown by curve a of Figure 6. 

In aural work it was found that 


with 



SF{ty 

TIf'^ 


dt, 


(55) 


where ro(^) is the correlation function of the 
input noise without the carrier or central fre- 
quency. Here Sa/ua is the rms audio signal-to- 
noise ratio perceived in the earphone, and A/e is 
the width of a rectangular earphone filter re- 
sponse. The corresponding expression for the 
linear rectifier becomes 


liA = To.o r” r SFjty 

\nal lin T(2A/e)i J-00 L 
where 70.0 



= {i:[ 


(2nV. 


2^" n \ (n + 1) \ 


If: 


Toity^ + 2 dt 


Again, if the signal-to-noise ratio is small, the 
second term in equation (56) may be omitted. 
For practical purposes the difference in behavior 
of the two detectors is important only when the 
second term of equation (56) becomes significant 
(see Figure 6, curve b). 

Quantitative Expressions. The optimum (or 


“matched”) i-f filter is the conjugate of the 
Fourier transform of the pulse, not only for visual 
reception, as has been previously determined, 
but for aural or meter reception as well. The 
addition of a video filter to such an i-f design 
theoretically offers no improvement in visual 
reception under ideal conditions (which appar- 
ently are in general not quite realized experi- 
mentally). Then if co represents sf/uf at match, 
the results of the analysis^^^ may be summarized 
quantitatively. For, knowing the values of the 
physically minimum detectable signal-to-noise 
ratios for the various types of presentations — 
A scope, ungated or gated aural reception, and 
use of a meter — it is possible to calculate and 
compare the relative and absolute sensitivities 
of these methods. The use of a gaussian pulse 
and filter was assumed, since the gaussian shape 
is a reasonable approximation to actual shapes 
used in practice. 

Under this assumption the following relations 
were derived for the case of visual methods of 
indication. 


- 

\nv ! quad 


(“) 

\WF/li 


(57) 


= 0.957<7§ (1 - 0.1526<To), <^1 g 10, 

/lin 

at match. 

For aural reception the necessary formulas for 
ungated noise are 


0.633(rg 


(58) 


(1 - 0.1246(7o), (tI ^ 10, 


(njquad T^iAfe/b)^' 

/^\ ^ OMQal 

\njlin ToiAfefb)^' 

where To is the pulse period, at match, and /& is 
a frequency relating the width of the pulse (or 
filter) to its duration; that is, the pulse is pro- 

portional to e ^ , co6 = 27r/5. Here A/e is the 
width of the critical ear or audio filter, which- 
ever is the narrower. When the background is 
gated, equation (58) becomes 
^ Q.633(7g 

/quad {T qT oAf ef b)^ 

(59) 

- 0.1246<r„), g 10, 

WaG/lin {T TgAj ej b)^ 

where now tg is the duration of the “on” or 
transmitting period of the gate. 


(~) 

\naGl qi 


STUDIES OF JAMMING SIGNALS 


95 


The expression for the periodic meter (still for 
gaussian pulses) was shown to be 



at match, where the second detector of the re- 
ceiver may be either linear or quadratic. In 
equation (60), Smlum represents the ratio of the 
rms signal to the rms noise detected by the 
meter, and A/„» and A/a are widths of rectangular 
meter and audio filters equivalent to the actual 
gaussian ones assumed. The equivalence is 
given analytically by Jk = A/a/tt* = 0.565A/i^, 
where K is an arbitrary subscript. The quantity 
appearing in equation (60) is twice the 
equivalent rectangular filter width of the meter. 

Summary of Results. A comparison of absolute 
sensitivities of the various methods is shown in 
Table 4, constructed on the assumption that the 
pulse is gaussian and the filter is matched to it. 
The various constants are /& = 4 • 10^ c, the 
width between half-power points is 2/3 me, and 
the equivalent rectangular pulse is 7.1 X 10^ c. 
Further, the total duration of the gate is tg = 
5 • 10“® sec, and To = 10“^ sec (prf = 10^ c). 
Two different audio filters are used: A/e = 50 or 
5 c; and three different meter filters: Afm = 2, 
0.2, or 0.1 c (actual width 1, 0.1, or 0.05 c), each 
with the same audio filter A/e = 50 or 5 c. 

The aperiodic meter has the advantage of not 
requiring knowledge of the prf and has poten- 
tially great sensitivity if spurious fluctuations in 
gain can be balanced out. The periodic meter is 
less sensitive to gain fluctuations, but it is in- 
correct to assume that the signal-to-noise ratio 
is as favorable for a moderately narrow audio 
filter and a final very narrow meter filter as for 
a single audio filter having the same width as 
the latter. See, for example. Figure 7. Meter 
methods can he made more sensitive than the A 
scope if long time constants are available, and this 
depends on tactical considerations. Gating is also 
necessary. 


Curves were drawn*" to show the power re- 
quired to achieve a given signal-to-noise ratio as 
a function of pulse length and i-f filter width, 
when the pulse and filter are not matched to 
each other (i.e., are not related as Fourier 
transforms). Figure 8 is included here as an 
example of these. Although the best i-f filter is 


Table 4. Comparison of sensitivities of visual, aural, 
and meter methods of presentation.* 




Quadratic 

Linear 


At match 

2nd detector 

2nd detector 

Physically minimum 

A/, A/. 

A/e 

A/e 

A/e 

detectable signal 

50 c. 

5 c. 

50 c. 

5 c. 

(Visual) 

0.0 db (pessimistic) 

<ro= 0.0 db 

+1.0 db 

\sv/nv) 

-5.0 

-2.5 db 

-1.7db 


— 10.0 (optimistic) 

-5, 

.Odb 

-4, 

,4db 

(Aural) 






(Sa/na) 

-t-10.0 (pess.) 

+13.5 

+8.5 

>13.5 

+11.2 

no gate 

0.0 (opt.) 

+8.5 

+3.5 

>13.5 

+4.8 

(Aural) 






{Sa/ 'Hqg') 

-f-10.0 (pess.) 

+2.0 

-3.0 

+2.9 

-2.5 

gate 

0.0 (opt.) 

-3.0 

-8.0 

-2.5 

-7.8 



Afm 

Time 
constant 
= 2! Afm 

\ / at match 

/ Power required for 
cr minimum detecta- 

Ible signal. 

Periodic 







metering 

2 c. 

1 sec 

-6.7 

-9.3 

-6.3 

-9.0 

(Sm/Um) = 

0.0 db 
gated noise. 


10 

-9.3 

-12.0 

-9.0 

-11.5 

lin., rect. 

Ko 

20 

-10.0 

-12.4 

-9.8 

-12.2 

Aperiodic 







metering 

2 

1 

-10.0 

-9.7 

(s„j/?2wi) — 

% 

10 

-15.5 

-15.2 

0.0 db 

Ko 

20 

-16.5 

-16.3 


*The equivalent rectangular pulse is 1.41 /isec long. To = 10"^ sec, 
Tg = 5-10-® sec; fb = 4-10® c. 


the Fourier transform of the pulse, in aural re- 
ception the best pulse is not the Fourier trans- 
form of the filter (though it is in visual), for the 
problem of varying the filter with a fixed pulse 
is not the same as that of a fixed filter and varying 
pulse. Instead, the best results in meter or audio 
detection are obtained by using long pulses. 
h Figures 7 to 11 of reference 585. 


96 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


The dependence of necessary signal power on 
the prf was studied, and found to be different in 
visual and aural detection. The variation with 
gating and audio filter width was also examined, 
and the results are illustrated by Figure 9. It 
was further established^^^ that long pulses are 


whole quite adequate for the purposes described 
above, was foimd to be insufficiently refined 
when the detailed question of integration, by 
eye or by mechanical devices, arose. Accord- 
ingly a number of studies were begun on this 
problem, not only to provide theoretical guidance 



1 1.5 2 2.5 3 U 5 6 7 8 9 10 15 20 25 3 0 40 50 60 70 80 90 100 ISO 2 OO 250 300 400 500 600 800 1000 


X 

Figure 7. Width of the equivalent earphone filter A/e used in aural detection of the minimum detectable 
signal in the presence of noise as a function of the audio filter width A/a used in meter detection of the 
same signal-to-noise ratio uo. 

_ A/e _ Width of single audio filter, or filter used in aperiodic metering, A = 1 
^ A/m ~ Width of periodic meter filter 

A/o Width of audio filter used with meter 

A/m Width of periodic meter filter 

ao = Minimum detectable signal-to-noise ratio in periodic metering scheme 

A = Minimum detectable signal-to-noise ratio in periodic metering scheme 
Minimum detectable signal-to-noise ratio in “ear scope” or, when A = 1, 
in aperiodic metering system 


more easily detected for given mean input power, 
whereas in visual detection the pulse length is 
immaterial (to a first approximation). 

Effects of Integration on Signal Visibility 

The criterion estabhshed in the earlier work^®^ 
for the signal-to-noise ratio, although on the 


or confirmation of experimental work being 
carried out by the AJ investigators at the time, 
but to suggest, if possible, improved AJ tech- 
niques. 

Early Qualitative Approach. One of the first 
problems investigated was the effect of integra- 
tion on the visibility of weak signals through 


INPUT POWER (ARBITRARY UNITS) 


STUDIES OF JAMMING SIGNALS 


97 



01 .02 . 03 . 05 . 08.1 .2 . 3 . 5 . 8 I 2 3 4 5 6 78 910 20 30 40 60 100 


\ 

Figure 8. Input power to the intermediate frequency as a function of i-f filter width for aural reception 
of the minimum perceivable signal, gated or ungated noise. 



Tc<(l/PRF) 

Figure 9. Input power to the intermediate f req^iency -^s. a function of pulse period for aural reception, 
at match, with ungated noise. '' ■ * ' ■ 



98 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


noise on a standard A scope (deflection modu- 
lation).®^^ The general form of the probability 
distribution®^®’ for the envelope of signal 

and noise is 

Pin, <T)dn = 2ne- Joi2ian)dn, = - 1, (61) 

where 

_ Envelope of signal and noise 
^ Rms voltage of noise envelope’ 

_ Voltage amphtude of signal 

Rms voltage of noise envelope 
_ Rms voltage of signal (carrier removed) 

Rms voltage of noise 

The characteristic of the detector-plus-ampHfler 
combination is usually hnear or square law, and 
can be made square root; that is, the output 
p equals n"^, where n = 1, 2, or H, respectively. 
Then we have 

P(p, a)dp = Pin, o)dn = 

Po(p)e-‘^' Jo(2zVpV«)dp, (62) 

where 



From equation (62) it is possible to compare, 
say, the linear and quadratic displays, by setting 
the “contrast” ‘ ratios equal: 

P(pi,0) P(p2,0)’ 

in order to determine the relation between pi and 
P 2 which makes the brightness ratios of equation 
(63) equal for the same value of c. In general, 
the conditions under which a signal is visible 
through noise on the oscilloscope screen are: an 
average contrast of at least 1.02 to 1.04 at a 
deflection where there is sufficient brightness to 
make the contrast visible and sufficient homo- 
geneity to allow the eye (and brain) to average 
accurately. Moreover, for the same signal-to- 
noise ratio these studies®^® indicated that the 
quadratic display requires a longer integration 
time than the usual linear display — or, con- 
versely, that for the same time of integration the 
minimum visible signal is larger for the quadratic 
display. Similarly, a square-root or logarithmic 
display seemed better than the linear. These 
investigations were limited to deflection-modu- 
lated presentations. 

’When P(p,<t)/P(p,0) < 1, then its reciprocal is 
termed the contrast. 


Quantitative Approach. It was found, however, 
that the above approach was still too naive. 
The integration time did not appear explicitly 
in the analysis, as it should in any theory of 
this type, nor was the case of intensity modula- 
tion examined. A more refined examination of 
the problem showed that what the eye averages 
is brightness, a quantity also directly related to 
the display characteristic of the system. In in- 
tensity modulation the observable “pattern” is 
directly proportional to the observed brightness 
or intensity and to the video output voltage. 
In deflection modulation, the eye still averages 
brightness, which is not now directly propor- 
tional to the voltage but depends (as always) 
on the number of electrons striking a particular 
area under observation. This number, in turn, 
is influenced by the distribution of the amplitude 
of the wave of signal plus noise. The problem in 
the former instance is essentially two-dimensional, 
the range sweep being one degree of freedom and 
the brightness of the pattern, the other. In the 
latter case an additional “dimension” is used 
— namely, the (vertical) displacement of the 
electron beam. 

The problem was found to be less tractable 
than it first appeared, and was finally laid aside 
for more urgent work. A few prehminary results, 
however, might be mentioned. In intensity- 
modulated systems, firstly, square-law systems 
appeared to be 1.0 to 1.5 db more effective than 
linear, and about 2.5 to 3.0 db more effective 
than square-root devices, for integration times 
of the order of 0.5 to 5 sec. The effects of satura- 
tion in intensity modulation are always deleteri- 
ous. For deflection modulation, on the other 
hand, when the integration device is a camera 
which considers only a small rectangle of screen, 
it was found that square-root systems yield 
about 1.5-db improvement over the linear dis- 
plays and about 2.0-db over the quadratic, for 
the same integration times. With photographic 
integration, however, intensity-modulated dis- 
plays appear to be more effective than deflection- 
modulated ones for short integration times (up 
to 4 or 5 sec) and less effective beyond that. 

It was further observed that in intensity mod- 
ulation, with the three types of display charac- 
teristic considered in = 1, 2), the best value 

of bias is zero when a simplified form of criterion 
is used which omits the contrast term e6(0) 


STUDIES OF JAMMING SIGNALS 


99 


(b(0) = the mean brightness without signal). 
When the contrast constant e is different from 
zero (0.04 is a reasonable value), there exists a 
nonvanishing optimum bias, which increases with 
longer integration times. 

The analysis of deflection modulation where 
the integrating device is a camera was carried 
out for two special cases: (1) a small area element 
of the scope screen, and (2) a narrow vertical 


Laboratory of the Massachusetts Institute of 
Technology on problems of this general nature, 
and theoretical studies similar in nature to the 
above were also made there. • 

Other Applications of Noise Studies 

While much of the work was concerned with 
the analysis of spectra and the study of the 



FREQUENCY IN Me 


Figure 10. Spectrum of the distribution curve of overall transit time of the electrons descended from a 
common primary. 


strip of screen, of moderate height Ar. It was 
shown that an optimum value of Ar exists. The 
complete theory demands, however, that the 
area effectively viewed by the eye (or camera) 
also have a reasonably large width Aw, with the 
result that correlation between the traces entering 
and leaving the area must be considered. It was 
at this point that analytical difficulties and other 
more pressing problems forced abandonment of 
the work. 

Detailed experiments, however, were carried 
out throughout World War II at the Radiation 


jamming properties of noise against pulsed sig- 
nals, some efforts were made to determine 
analytically the spectral nature of the output of 
some of the noise sources used in jammers and 
to apply the results of the fundamental studies 
to other problems which arose. 

Noise Output of Photomultipliers 

Among the earliest of such studies was a cal- 
culation of the frequency spectrum of the noise 
output of the RCA 931 photomultiplier tube .^22 
It was discovered that this tube might provide 


100 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


a suitable direct source of noise in the frequency 
band of the enemy’s radar and communications 
equipment. Accordingly, a theoretical estimate 
of the frequency dependence of the noise output 
from this tube was undertaken. 

On the assmnption of high vacuum and negh- 
gible space charge, it was found that the noise 
output falls olf as the frequency increases, 
because of (1) the finite velocities of the electrons 


drop 6 db around 500 me. These frequencies 
may be increased by raising the accelerating 
voltage, the increase being somewhat more than 
proportional to the square root of the voltage. 
Another method of extending the spectrum is to 
increase only the last two interstage voltages, 
the preceding ones being left unchanged. Raising 
each of the last two to 400 v results in the spec- 
trum being down only 4 db at 600 me. Some 


UJ 



FREQUENCY IN MC 


Figure 11. Calculated spectral energy distribution of the noise from the RCA 931 tube. 


as they approach the anode and (2) the spread 
in time of arrival at the anode, of the electrons 
descended from the same primary. The spectrum 
is flat at low frequencies but approaches zero as 
the frequency is increased; this result is evident 
from Figures 10 and 11. When the tube is 
operated with 70 v per stage, the output should 
be down about 1 db around 200 me but should 


increase in the preceding interstage voltages, 
however, may be necessary to prevent excessive 
distortion of the electron orbits. Then, with a 
net accelerating voltage of about 1,500, and the 
interstage potentials increased to 400 in the last 
two stages, the 931 might be an adequate noise 
source in the 550- to 600-mc range. (Because of 
approximations in the calculations, and varia- 



STUDIES OF JAMMING SIGNALS 


lOI 


tions in the dimensions of individual tubes, the 
numerical results above may not be more ac- 
curate than ±3 db.) 

Noise Output from Gas Tubes in Magnetic 
Fields 

Experimental work on noise sources (see Chap- 
ter 2) indicated that an excellent source of high- 
level, wide-band noise could be obtained from a 
low-pressure gas-discharge tube when a magnetic 
field of suitable strength was applied. A theo- 
retical study^ was undertaken in an attempt to 
explain and predict the nature of the spectral 
output of such tubes. 

It is well known that in the so-called plasma — 
a region in a gas discharge where the number of 
positive ions is equal to the number of negative 
ions of equal charge and the ion density is uni- 
form — tree oscillations of the ions may occur 
with well-defined frequencies. These frequencies 
depend on the ion mass, the ion charge, and the 
ion density, and on nothing else, provided ther- 
mal motion is neglected. It is easily shown that 
for ions of a given charge sign, the frequency is 
given by (cp/ttM)*, when e = ion charge, M = 
ion mass, and p = charge per unit volume due 
to ions of one sign (or the other). That is, high 
ion densities give rise to high oscillation frequencies, 
an observation on which the qualitative results 
of the analysis are based. 

Results of the Analysis. If an electron current 
per unit area /o leaves the cathode, the rate of 
ion production per unit volume is 

where / is the electron mean free path of ioniza- 
tion and X denotes the position between cathode 
and anode; the quantity Uo is (2Uo^cV^^“)^ 
where Vo is the potential at a flat portion of the 
orbit, m is the electron mass, c the velocity of 
fight, e the charge on the electron, and H is the 
magnetic field strength (in gaussian units). The 
distribution function / = /(x, v) is defined as the 
number of ions per unit volume at position x, 
per unit velocity range at velocity v. In other 
words, /(x, v)dxdv is the number of ions (per unit 
cross-sectional area) between the planes x and 

jPart III of reference 730. 


(x -f dx) having velocities between v and (v dv ) . 
The function / assumes finally the form 

/ = 0 D{v), (65) 

where D is defined as Z)(i; < 0) = 0, D(v > 0) = 1, 
and equation (65) is the representation sought. 
Furthermore, the quantity </> = with 

W = + eV, is a function solely of the 

total energy of an ion at x having velocity v. 
The form of the functional relationship between 
4> and W is determined through the initial con- 
dition (i; = 0); namely. 


<t>ieV) = 


-^(x) 
m dx 


(66) 


The relation governing the potential distribution 
V{x) is given by 


d?V 

dx^ 


-27r 



^ >S(xo)dxo 

Vv{xo) - v{xy 


(67) 


For the special case of equation (64), which 
applies to the present problem, it is found that 

V = -12a( 


(eao = -Ax^ (68) 


and for (l>(W) when i; ± 0, we have 


0(1F) 


6 IpMao^fy 
5 eHA \ 


^5/3 


M 

2eA 



(69) 


In the calculations it is assumed that only a 
small portion of the mean free path of ionization 
of the electrons is spent within the ionizing 
region. Under actual conditions of operation 
this assumption is well justified. The further 
assumption that the potential drop within the 
ion-forming layer is negligible compared with 
the ionizing potential is also justified. It is, 
moreover, interesting to know what magnetic 
field strengths are required to turn the electron 
paths back toward the cathode before the free 
path of ionization is totally spent. In other 
words, how large must H be in order that in- 
finite ion densities result? To an order-of- 
magnitude approximation, the critical value of 
H = {Hf) is that for which ao just equals Z; 
is then about 140 gauss, the field strength for 
which h-f response of noise exists. The more 
complete analysis^^° showed that for tubes of the 
general specifications of the 6D4, for example. 


102 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


appreciable oscillations at frequencies around 
250 me could be expected. 

Effect of Clipping on Noise Spectra of 
Gas Tubes 

It was found that clipping or distorting the 
waveform of the noise output of one of the above 
tubes, preferably the 6D4 (as its spectral level 
is considerably higher than that of the RCA 931), 
resulted in spreading of the spectrum.^^® Since 
broad spectra are needed in jamming, as is dis- 
cussed elsewhere (see Section 6.2.1), an analytical 
study was undertaken to determine numerically 
the effects of limiting when the incoming wave 
consisted of random noise from a 6D4, 884, 178A, 
or 2D21 gas-tube noise soiuce. The nonlinear 
devices examined were linear and quadratic 
rectifiers, with various cutoff and saturation 
voltages. The mathematical results are siun- 
marized in Section 6.2.1, equations (21) and (44). 
The qualitative results^®® for the 6D4 spectrum 
are outlined below. 

Results for the 6D4 Tube. Chpping, whether 
at the “top” or “bottom” of the wave or both, 
always spreads the spectrum. For saturated 
nonlinear devices (or rectifiers, as they are often 
called), this spread is greatest when the ratio 
bo/xl/^ of cutoff voltage (measured from the 
operating point) to rms input noise voltage lies 
between 1.0 and 2.0 or between —1.0 and — 2.0. 
For larger ratios the level of the output spectrum 
may be prohibitively low. It is further observed 
that chpping without saturation yields even 
greater spreads, and at higher levels, than do 
overloaded rectifiers operating under conditions 
otherwise the Same, except for the parts of the 
spectra well away from the maximum. There is 
not a great difference between saturated linear 
and quadratic detectors so far as an increase in 
the width of the output spectrum is concerned. 
However, in many situations a linear dynamic 
response may be preferred for its generally higher 
output spectral levels, other factors being the 
same. 

For optimum spread it is desirable to clip 
as heavily on the bottom as possible (i.e., 
bo / ^ 1.0), but within the limits of available 
gain. It is also desirable to operate with little 
or no overloading, if practicable. Symmetrical 
chpping, where the operating point lies midway 
between cutoff and saturation, is unsatisfactory 


from the above point of view, as it does not 
yield sufficiently wide, high-level spectra. Ex- 
treme chpping, with (bo/ > 1.0), gives a good 
spread, but at prohibitively low levels. As noted 
before (see end of Section 6.2.1), the power in 
the d-c and continuous portions of the output 
are independent of the spectral shape. As 
chpping becomes more severe, a greater per- 
centage of the output power is concentrated in 
the continuous spectrum, although the absolute 
level drops rapidly as bo/xl/^ is made more posi- 
tive — that is, as the bias is made more negative. 
Figures 12 to 16 illustrate the general nature of 
the results. 

Noise Transformers 

Not only was the general analytical technique 
for the treatment of noise applied to specific 
problems involving jamming spectra or the out- 
put characteristics of noise sources, but also 
to other important questions involving noise. 
Among the latter was the problem of noise in 
transformer cores (see also Section 2.6). An 
approximate theory was accordingly developed 
for the eddy-current loss in transformer cores 
excited by h-f sine waves and by broad-band 
(video) random noise. Some of the salient 
features of the analysis are outhned below. 

Mathematical Analysis. First the boundary 
conditions were established, subject to which 
the field equations governing the distribution of 
the electric and magnetic fields in thin rectangu- 
lar laminae must be solved. Then the skin 
depth 5o and the mean eddy-current loss W were 
determined for current- and voltage-fed trans- 
formers. The skin depth was defined here as the 
depth measured from the surface at which the 
eddy-current losses, due to the induced currents, 
are a fraction C (C < 1) of their total value. 

For sinusoidal excitation, analytically a special 
case of the noise problem, the skin depth is 
specified by the relation: 

^ _ Q _ sinh Xq (1 — bo/ a) — sin Xp (1 — bo/ a) 
sinh Xo — sin Xo ’ 

0 < C < 1, (70) 

where Xo = (2oioiJie(^a^)\ with an effective 
permeability, a the conductivity, coo = 27r/o = 
the angular frequency of the exciting field, and 
2a the lamination thickness; here C is taken to 


STUDIES OF JAMMING SIGNALS 


103 



O.b 1.0 1.5 2.0 2.5 3.0 3.5 ^.0 4.5 5.0 

MEGACYCLES/SEC. 


Figure 12. Spectrum of the 6D4 with approximation spectrum. 



0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

MEGACYCLES/SEC 


Figure 13. Spectra of the 6D4 after clipping and rectification of the input (random) noise by biased 
and saturated linear rectifier. 


104 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


be 0.90. The mean eddy-current loss (per unit 
volume) is, when Xo ^ 0.10, 

n'^n- / ViUol \2 1 (j^pa/XeCrCOo)- 


' (/3oa<r)2\V2/?„i/y 3 1 


+ OodMeCrWo)® 

I 6 10^ 


(71) 


where now Uoi is the peak amplitude of the sinu- 
soidal voltage applied to the primary, Ni and Roi 
are the number of tinrns and the resistance of the 
primary, respectively, while I is the mean length 
of the magnetic circuit. The quantity )8o is 
{Li/Rqx -f L2/R02), Li and L2 being the 
primary and secondary inductances. The effects 
of capacity are ignored. When Xo > 0.10, we 
may write 


lEii = 


(iSoacr)' 


/ Y 

\ V2R011I 


(1 

Uo 


sinh Xq — sin Xo 




102. (72) 


^ Xo sinh Xo — cos Xo ^ 

The condition ^o/a ^ 10^ is a usual one in 
practice. For a uniform band of noise applied 
as a voltage to this primary, these results (70) 
to (72) are modified to 

sinh X (1 — 8 q/ a) — sin X (1 — 80/ a) ^ 

/x, cosh X — cos X 

0.10 = ■ 




'dX 


f 


2 sinh X — sin X 


dX 


^ 102, (73) 


cosh X — cos X 

& 

a 

where C = 0.90, and Xi ,2 = (2jue o-a^ coi^2 )^ oji 
and C02 being respectively the lower and upper 
hmits to the uniform spectrum. The eddy- 
current loss per unit volume in this instance 
becomes 


a^o- 


Wi = 


/ TCU. 

\ Ro\i^ h 


tan~ ^(j9oa/Xeg'^2) — tan~^()goa/Xeq'coi ) ”1 

/3oa/XeO-(co2 — oil) J’ 

^ S 10^ Xi < X2 S 0.10, 


1 -- 


(74) 


fjT- Cl O' 


Wu = 


tan" 


/ \ 

\ K.P I 

.(^\ 

ytanh|y 


4 

x^x; 

— tan" 



a 


^ 102, X 2 > Xi ^ 0.10, (75) 


where now V'ii is the mean-square noise voltage 
applied to the primary. Curves illustrating 
equations (71), (72), (74), and (75) are shown 
in Figures 17 and 18. 

The above formrdas apply for voltage-fed 
transformers, /3o > 0; in the case of current 
feeding (/3o = 0) it was found that the expansion 
for the skin depth 5o became 


/: 


sinh X ( 1 — gp/g) — sin X ( 1 — gp/ a) , 
cosh X + cos X 


C 


n x^(5i 

JXl \cc 


sinh X 


dX 


\cosh X + cos X/ 

0 < C < 1 (76) 

where a uniform mean-square current spectrum 
has been assumed. For the eddy-current loss 
per unit volume, we have 

w = {NUT + NUT)- 


r I u 


X^ 


sinh X — sin X 


rfx], 


(77) 


cosh X + cos X 
where now If and /| (the latter often zero) are 
the mean square apphed primary and secondary 
currents, respectively, and N2 is the number of 
secondary turns. 

Results of Analysis. Among the results it was 
found that the skin depth decreases, as one would 
expect physically, with increasing lamination 
thickness, frequency, core conductivity, and 
effective permeabihty iie. The mean eddy-cur- 
rent loss in the constant-voltage transformer 
diminishes with increasing frequency or spectral 
width, because of skin effect, and increases with 
the thickness of laminae. For voltage-fed trans- 
formers W varies approximately as the inverse 
square root of the bandwidth. On the other 
hand, W in the constant-current cases is observed 
to vary about as the square root of the band- 
width.761 


Studies of Frequency Modulation 

An investigation of the properties of f-m waves 
was carried out, with the purpose of providing 
information about the possibly suitable jamming 
characteristics of such waves. As discussed else- 
where (Section 6.2.1), frequency modulation by 
noise was early considered a promising line of 
investigation. Then, too, frequency modulation 


STUDIES OF JAMMING SIGNALS 


105 


by periodic waves, such as the sinusoid, or it was found that the modulated wave E{t) is 


E{t) = I ./o I ^ j cos ^ ~ j [cos {o)c ” no}Q)t + ( — 1)” cos (coc + naJo)^] j-, (78) 


square, or triangular waves, offered possibilities 
for the jamming of communications, if not 
directly as a radar countermeasure. 

Study of Types of Frequency Modulation 

With communications jamming chiefly in 
mind, a study of four types of frequency modu- 
lation was begun. ^^2 analysis considered (1) 

sinusoidal frequency modiflation, (2) unsym- 
metrical sawtooth frequency modulation, (3) 
symmetrical sawtooth or “triangular’ ' frequency 
modulation, and finally (4) frequency modula- 
tion by a square wave. 

Sinusoidal Frequency Modulation. For (1), 


when E cis the peak voltage of the (unmodulated) 
carrier, co^ = 2'irfc is the carrier angular frequency, 
and Acu is the (angular) frequency deviation from 
the carrier; /o = a)o/27r is the rate at which this 
deviation is made, and Jn are the familiar Bessel 
functions of the nth. order, first kind. Here the 
ratio Aco/coo = AF//o is termed the modulation 
index and denoted by h — see the relation fol- 
lowing equation (2) . The mean-square amplitude 
of the ^th component is An^ = Jn^{b). The 
nmnber of significant sidebands is roughly 26 + 1. 
One characteristic of the spectrum is that it 
tends to peak at zLnf ^ zL b, i.e., at the limits 
of the band. 



0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

MEQACYCLES/SEC 


Figure 14. Relative spectral levels after rectification of the 6D4 output by linear and Type B quadratic 
rectifier (see Figure 5). 


106 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


Sawtooth Frequency Modulation. In frequency 
modulation by a sawtooth wave (2), the output 
wave E{t) may be resolved into an infinite num- 



- 3.0 - 2.0 - 1.0 0 1.0 2.0 3.0 


Figure 15. Power in the continuum after 
rectification and clipping of the input noise by 
a biased and saturated linear rectifier. 


her of components, on either side of the carrier , 
spectrally speaking. The square of the modulus 
of the Aith component has the form 




46 


(B^ + Bn) 


( 79 ) 


where the vectors Bn and B'n are given by 


B'n = ± C 




B 




( 80 ) 


and C and S are the Fresnel integrals 


cw ± .S(.) . 


dt. 


A qualitative picture of the relative magnitudes 
of An as a function of the modulation index h and 
the sideband order n may be obtained at once 
by considering a modification of Cornu’s spiral 



- BIAS LEVEL MEASURED FROM b^/yp^ 

C = SATURATION LEVEL OPERATING PT. 


= MID-TRANSMISSION WIDTH VOLTAGE 
FOR THE TYPE-B QUADRATIC RECTIFIER 

Figure 16. A comparison of the percentage of the total output in the d-c and continuum, after linear 
or quadratic rectification. 




STUDIES OF JAMMING SIGNALS 


107 


shown in Figure 19. For large h, and conse- 
quently large values of (6 ±ny Tr/2h, the vectors 

and B'„, with their terminations on the spiral 
as shown in Figure 19, circle around the point J 
in ever decreasing spirals as 7r(6 zb nYI2h in- 
creases, provided (b—n) > 0. When (b—n) < 0, 
B,^ circles around J'. The resultant of the two 
vectors is large for (b — n) > 0, and is quite 
small for (b — n) <0, becoming smaller as n 
increases for a given b. As tz progresses through 
integral values, and b is large, the vector sum 
B„ + B'n oscillates somewhat but keeps a com- 
paratively large average value, until b < n, 
whereupon the resultant decreases rapidly and 
approaches zero amphtude for extreme values of 
n. As 6 -> GO , the spectral half- width approaches 
AF, the extent of the frequency deviation. The 
spectral distribution is discrete, as before, but is 
reasonably uniform, as can be seen from Fig- 
ure 20. 

Triangular'^ Frequency Modulation. For fre- 
quency modulation by a symmetrical sawtooth 
wave (3), the mean-square amphtude of the ^th 
component is 




cos 




( 81 ) 


and here again the vector diagram. Figure 19, 
may be apphed to show how the magnitude of 
each component changes as n increases. The 
effect of the trigonometric factor in equation (81) 
is to cause a fluctuation in the length of the vector 
resultant shown in Figure 19, a fluctuation which 
is rapid for smaU values of the modulation index 
b, smaU n, and which becomes more rapid as n 
is increased. Moreover, as b is made larger, the 
osciUations also become more rapid. This is the 
analytical reason why the spectra of the saw- 
tooth and symmetrical sawtooth frequency mod- 
ulation differ so much in character, as seen in 
Figure 20. 

Square-Wave Frequency Modulation. The prob- 
lem of frequency modulation by a square wave 
has been solved,®^^ the resulting expression for 
the modulated wave being: 


The mean-square amplitude of the nth. com- 
ponent is 


I p = 


462 


7r(6 — n) 


(62 - n 2)2 


( 83 ) 


For large modulation indices, and of course con- 
stant deviation AF, the energy of the original 
carrier is observed to be concentrated more and 
more in two pairs of sidebands, a pair on either 
side of the carrier and approximately the half 
bandwidth AF from it. When the sweep is very 
slow, corresponding to 6 — oo , each pair becomes 
a single, discrete sideband at dzAF from f^. 
This is understandable from a physical point of 
view, since in the hmiting case 6 oo , the signal 
energy is present at + AF half the time, and 
at /c — AF the other half, and the amount of 
energy at a given frequency is proportional to 
the time the wave spends at that frequency. 


Conclusions from the Study 

With the above analytical details in mind, it 
was possible to outline the requirements of a 
possible use of frequency modulation in conjunc- 
tion with amphtude modulation or frequency 
modulation by noise^25 for barrage jamming radar 
or communications systems. Frequency modu- 
lation was to be used to provide as wide and as 
uniform a barrage as possible. These require- 
ments are outlined briefly as follows. 

1. Proper spacing between f-m sidebands. For 
radar jamming, the minimiun permissible side- 
band separation /o should not be less than about 
one-half the effective video bandwidth of the 
receiver being jammed. For communication 
jamming about one-half to one-flfth the audio 
bandwidth was suggested. The maximum per- 
missible separation should be about one-flfth or 
one-sixth the half barrage width AF. 

2. Spectral uniformity. Spectral uniformity 
should be obtained with reasonable satisfaction 
for radar jamming if the half barrage width lies 
between a lower limit of about 5 times and an 
upper hmit of at most about 25 times the f-m 
sweep rate /o. For communications jamming the 



in — ( 

— ~ cos -f ^ 


108 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


half barrage width may be from fifty to several 
thousand times the sweep frequency. 

3. Type of frequency modulation used. For 
radars, either sinusoidal frequency modulation 
or symmetrical sawtooth frequency modulation 
was suggested. (However, a sawtooth wave is 
preferable spectrally, if practicable at these fre- 
quencies.) For communications, symmetrical 
sawtooth frequency modulation should be used; 


modulation to “fill in” the spectriun should be 
about three-fourths the sideband separation /o, 
so that holes in frequency will not occur. 

Jittered Frequency Modulation 

Some effort was also made to investigate the 
effect on the response of a detector to “jittered,” 
slow frequency modulation, The work is of 



2a LAMINATION THICKNESS 


Figure 17. Mean eddy-current loss (per unit volume) for constant voltage transformers excited by a 
sine wave. 


sawtooth frequency modulation is again to be 
preferred, if obtainable. 

4. Modulation index: b = AF/fo. For radar 
work, 5, 6, < b <25; for communications, we 
have 50 ^ 6 ^ 3,000. The limits on the modu- 
lation index vary with the receiver character- 
istics. The width of the band of noise amphtude 
modulation or frequency modulation that is 
used with the various types of periodic frequency 


interest primarily in connection with communi- 
cation jamming. It considered the character of 
the response of a receiver to a superposition of 
slow, regular, periodic (e.g., mechanical) fre- 
quency modulation of wide deviation and a 
jittering or noise frequency modulation of smaller 
swing. The spectrum was found to consist of 
two parts: a continuous background and a dis- 
crete portion confined to frequencies (measured 



STUDIES OF JAMMING SIGNALS 


109 


relative to the carrier as origin) which are mul- 
tiples of the slow-scanning frequency. Presum- 
ably, the discrete portion should be minimized, 
as it excites only certain nerves of the ear. It is 
observed that half of the energy lies in the con- 
tinuum (the best obtainable fraction), if the 
jittering has sufficient rapidity and amplitude 


Simultaneous Frequency Modulation and 
Amplitude Modulation 

One further problem of some interest that was 
examined briefly^^^ concerned the presence of 
simultaneous frequency and amplitude modula- 
tion in the output of self-excited, u-h-f oscillators. 



2 3 5 6 7 8 9 10 II 12 

OR f2 MEGACYCLES 


Figure 18. Mean eddy-current loss (per unit volume) for random noise with constant mean-square 
input voltage and a uniform spectrum. 


SO that a receiver is traversed by the frequency 
several times per half-scanning period. Instead 
of several traversals per scan, it is also sufficient 
if there is enough jittering so that the traversal 
time varies materially from scan to scan. The 
mathematical model used in the analysis of the 
problem is that of a square rectifier exposed to 
a collection of random pulses. 


To gain an approximate understanding of the 
operation of such tubes, an idea of the magnitude 
of the frequency modulation and its phase rela- 
tion to the amplitude modulation is desirable. 
In practice, this may be best achieved by 
measurement of the spectrum when the oscillator 
is amplitude-modulated a fixed percentage by a 
sine wave of known frequency. By matching 


110 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


the experimental voltage spectnim with the cal- 
culated one, in cut-and-try fashion, the degree 
of incidental frequency modulation may be 
determined. 

6 3 TRANSMISSION AND REFLECTION 
OF ENERGY 

When radar or jamming signals are used. 


jamming, which seeks to invalidate the enemy’s 
radar and communication systems through his 
own emitted signals. The basic idea is to intro- 
duce a device or devices which reflect the original 
wave in a confused and heterogeneous manner, 
thus negating any information which might be 
reflected. A large and important class of pas- 
sive jammers used in RCM falls under the general 
heading of “confusion reflectors” (Window), 



energy is ultimately propagated through space 
in the form of electromagnetic waves, which 
strike targets and are reflected by them, with a 
resulting measme of information (or lack of it, 
depending on the nature of the transmitted 
wave). For radar signals, the echoes convey 
certain intelligence; in jamming, this inteUigence 
is partly or completely destroyed. In the sec- 
tions above, some of the theory behind “active” 
or electronic jamming has been discussed; but 
there is another large and effective field of 
countermeasures to be considered — “passive” 


whose theoretical characteristics are outlined 
below. A discussion of the practical details of the 
design and use of Window is given in Chapter 12. 

^ Studies of Reflectors 

Window is a term designating passive jammers 
whose purpose is to reflect and return trans- 
mitted radar signals in a random fashion, so that 
the echo pips are distorted and without distin- 
guishing features. This can be accomplished 
by “sowing” suitably designed conductors in the 


TRANSMISSION AND REFLECTION OF ENERGY 


III 



Figure 20. A comparison of four different types 
of frequency-modulation spectra. Type I is fre- 
quency modulation by sine wave, Type II by 
unsymmetrical sawtooth wave, Type III by 
symmetrical sawtooth wave, and Type IV by 
square wave. 

area or region to be concealed — either in the 
form of thin metal strips, or as long reflecting 


strands of metal, or in the form of corner reflec- 
tors. In this section, the theoretical methods 
and results concerning Window response are 
outhned. 

Chaff 

The design of Chaff (see Section 12.2.1) for 
countermeasures poses several problems, in- 
cluding the questions of (1) the optimiun dipole 
length for producing echoes at a given frequency, 
(2) the magnitude of the frequency band over 
which a particular dipole produces an appreciable 
echo, (3) the dependence of the radar response of 
Chaff on its cross-sectional dimensions, and (4) 
the effect of Chaff designed for one frequency at 
other bands in use for radar. 

The analysis is simplified considerably if the 
cross-sectional dimensions are small compared 
with the radar wavelength X. The Chaff can 
then be considered to be a circular cylinder of 
‘‘equivalent radius” a. For Chaff in the form 
of a flat strip of width d, the equivalent radius^^^ 
is given by 


a 


d 

4 * 


(84) 


If the cross-sectional dimensions are not small 
compared to X, then the response depends 
strongly on the exact cross-sectional shape. A 
detailed analysis of Chaff response was carried 
out.®°2 

The electric field of the incident radar beam 
induces currents in the Chaff. Once this induced 
current distribution is known, the field produced 
by it in the direction of the transmitter can be 
computed and the radar cross section can be 
evaluated. The determination of the induced 
currents can be made in several ways. 

Approximate ^'Engineering'' Procedure. Here 
one makes a judicious guess as to the form of 
the current distribution; for example, in the case 
of resonant dipoles one may assume a sinusoidal 
current which vanishes at the ends of the dipole. 
The amphtude of the current can then be fixed 
by applying the principle of conservation of 
energy. 

Solution of the Field Equations. If it is assumed 
that the Chaff material is a perfect conductor, 
then the tangential component of the total elec- 


112 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


trie field (incident + scattered field) must vanish solved by successive approximations to obtain 
at the surface of the Chaff. The mathematical the current distribution; and the radar cross 
formulation of this statement gives an integral section can then be obtained by evaluating the 
equation for the current distribution induced in flux back to the radar. The cross section a is 
the Chaff. This integral equation can then be given by 




+ 


2 sina:(l — sinx(l+i/) 
1-y 1 + 2 / 

2 sin x(l — y) sin x(l+?y) 
(l-y) ( 1 + 2 /) 


+ 2 [F'G' + F"G"] cos xy 
+ 2 [F'H' + F"H"] sinx!/ 


+ + G" 2 ] cos'^xy 

+ [H'^ + H"^] sin^ xy 
+ 2 [ G'H' + G"H" ] 




sin^ a;(l+ 2 /) sin^ x{\ — y) 


(i+# 


+ 


(1-# 


[ sin^x(l+ 2 /) sin^x(l — 2 /) 

/■, , .A, + 


sin 2 x 2 / 

22 / 

sin 2 x 2 / 
22 / 


(1+2/)' 
sin xy cos xy 
sin x{\ — y) 


r sin x{\^y) 

L 1+2/ 1-2/ 

r sin a:(l+ 2 /) _ sin x{\ — ij) 

L 1 +// 


(X-yY 

sin^ a:(l+ 2 /) 
( 1 + 2 /)^ 


sin^ x{l—y) 

{i-yY . 


1 - 2 / 


]}• 


(85) 


where x = —, 21 = length of Chaff; 

A 


y = cos 0 , 0 = angle between the direction of incidence and the axis of the Chaff; 

cf> = angle between the electric field of the incident wave and the plane determined by 
the dipole and the direction of incidence; 

a = equivalent radius of the Chaff, 

A 




fl' = 2 log 



1.154, 


2G' = 


-(O' — A) cos jSZ + (-1 sin 


[ (^ 2 ' — A) cos j(3Z — sin + [i (log 4/3/ + 0.577) sin cos ]“ 


J (log + 0.577) sin ■ 


2G" = 


cos jS/ 


[ (O' — A) cos /3/ — sin jS/ J (log 4/3/ + 0.577) sin i3/ — ^ cos /3/ ]- 


2 //' = 


(O' — A) sin — - cos j3/ 


7rII'‘ 


[ (O' — A) sin i3/ + ^ cos j3/ ]2+ [ J (log 4/3/ + 0.577) cos /S/ + 7 sin /3/ 
4 4 


■2H" = 


- [ i (log 4/32 + 0.577) cos (3/ + | sin /31 ] 


[ (SI' — A) sin /3Z + ^ cos /32 Y + [J (log 4/31 + 0.577) cos /3Z + ^ sin /31 ]- 


A = - (J log 01 + 0.288 - 1). 


TRANSMISSION AND REFLECTION OF ENERGY 


113 


If the Chaff is assumed to be oriented at ran- 
dom, the averaged cross section c is given by 

^ = (F'2 + F"2) (2ix- 1) + (G'2 + G"2)- 

\_2Trx + Sx log 2 (sin x cos a;) — 1 
+ J (cos- X — sin^ x) TT sin 2a; 

- 2 cos 2a; (log 4a; + 0.577) + (log4x + 0.577) 
+ (sin^ 2a; — cos^ 2a;) log 2] + 

[2Trx — Sx log 2 (sin x cos a;) — 1 

— i (cos- X — sin^ x) — w sin 2a; 

+ 2 cos 2a; (log 4a; + 0.577) + log 4x + 0.577 
-f (sin^ 2a; — cos ^ 2a;) log 2] 

+ 2 (G'H' + G"H")- 

[4a; (cos^ x — sin^ x) log 2 — sin x cos a;] 

+ i (F'G' + sin X 


— 4 COS a;(log 4a; + 0.577) — J log 2 (cos 3a;) 


+ 4 (F'H' + F"H‘ 


")[f 


cos a; 


— 4 sin a; (log 4a; + 0.577) + 4 log 2 (sin 3a;) J. 

( 86 ) 

As can be seen, the theoretical equations are 
rather forbidding. 

Conclusions from the Theory. On elementary 
theory the current will become large when 
4/ A = m, where m = 1, 2, 3, etc. In this case 
of resonance, the cross section will also be large. 
The equations given above show that the reso- 
nances occur at slightly longer wavelengths than 
those given by X = 4//m. As the radius of the 
wire increases, there is an increasing shift in the 
position of the resonance from 4Z/m, its position 
for vanishing radius. The position of the 
resonance is determined by solving the equation: 
odd res. 
m = 1, 3, 5. . 
even res. 

= 2, 4, 6. , 

where 


( cot i3z\ 
— tan j 


4 (12' -A) 


(l + €), (87) 


€ = ^ ^ T + 0-577)(n' - A) 

As an example, for 21 /a = 900 the resonances 
occur for 4Z/X = 0.95, 1.94, 3.93, 4.925. 

Figures 21 and 22 show the dependence of a on 
21/0 and 2Z/X over a wide range of values of 
the parameters. 

The unaveraged a depends on 6. Figures 23 


to 26 are examples of the angular patterns. A 
study was made of Chaff response as a function 
of polarization and angle of elevation.^^^ 

The simple theory gives o^/X^ = 0.153 inde- 
pendent of 21 /a. The more detailed theory gives 

^ = 0.184,0.194,0.204 

21 

for — = 900, 450, and 225, respectively. 

Rope 

Rope consists of streamers (see also Section 
12.2.1) whose length L is large compared to 
ordinary radar wavelengths X, and is generally 
made in the form of flat strips of width d. The 
random deviations of the Rope during its fall 
permit only small fractions of its length to 
scatter coherently. This results in eliminating 
any strong dependence of the cross section on 
the orientation of the Rope.^“^’ 

For Rope whose cross-sectional dimensions are 
small compared to X, use may be made of the 
concept^^^ of equivalent radius a. In this case 
(X> > a), the response to a wave polarized per- 
pendicular to the length of the Rope is negligible. 
For a fleld parallel to the Rope axis the cross 
section^^^ is given by 


KL\ 



where X is a constant determined by the devia- 
tions of the Rope from a straight line. 

If the cross-sectional dimensions of the Rope 
are not small compared to X, the theory becomes 
complicated. For a ribbon-shaped Rope of 
width d, the cross section can in general be ex- 
pressed as: 

cr = KAfic), (89) 

where A = Ld is the area of the ribbon and 
c = ttcZ/X. The solution of the scattering prob- 
lem was obtained numerically. For c < < 1 
(i. e., X > > Trd) the results agree with equation 
(88). If d is not small compared to X, radiation 
polarized perpendicular to the axis of the Rope 
is also scattered appreciably. In fact, for large d 
{d > > X) the cross section is independent of the 
polarization and is given by the expression for 
the cross section of a flat sheet. For perpen- 
dicular polarization the Rope may be considered 


114 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


to be made up of infinitely many infinitesimal tion of Rope as a function of wavelength is shown 
dipoles oriented across the Rope. Whend = X/2, in Figure 27. As can be seen from this figure, 
it may be expected that these dipoles will show Rope responds strongly over wide frequency 



Figure 21. Frequency response of Chaff ; average cross section. 


.90 
.80 

.70 
.60 
.50 

l'=rx .40 

.30 

.20 
.10 

0 .2 .6 1.0 1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2 4.6 5.0 5.4 5.8 6.2 6.6 7.0 7.4 7.8 8.2 8.6 9.0 9.4 9.5 10.0 

X 

Figure 22. Average response of Chaff. 



a resonant response. The strong coupHng be- bands. Its use is especially desirable at lower 
tween neighboring dipoles makes the maximum frequencies where Chaff becomes inconveniently 
broad and not very pronounced. The cross sec- long. 




TRANSMISSION AND REFLECTION OF ENERGY 


115 


“Tuned’’ Rope (a series of dipoles tied to- 
gether) had Httle appHcation. A crude theory 
was developed^^^’*^^’^^® for the case where the 
individual dipoles of the Rope are resonant to 
the radar frequency. Only the interaction of 
nearest neighbors was considered; this gives rise 
to a mutual impedance term which alters the 
gain of the individual dipoles. Then the scat- 
tering of the individual dipole sources was com- 


However, the dependence of cross section spacing 
is not critical. The cross section of a tuned Rope 
with optimum spacing can be compared to that 
of a “continuous” Rope of the same length. It 
was found that 

O'tuned _ 0.87X 

c* continuous 

where d is the width of the strip. Thus tuned 
Rope is much more effective {at resonance) than 



0 10 20 30 to so 60 70 80 90 100 110 120 130 140 ISO 160 170 180 

e 


Figure 23. Angular distribution of the response of Chaff (2 l/\ = 0.5). 



Figure 24. Angular distribution of the response of Chaff (2 l /\ = 1.5) . 


puted as in the case of an optical grating. The 
cross section of the tuned Rope depends on the 
spacing s between dipole centers. It reaches a 
maximum for 


continuous Rope. The effects of detuning from 
resonance, however, probably cause large holes 
in the frequency coverage; thus tuned Rope is 
more useful for beacon and identification use 
(fixed, known frequency) than for counter- 
measures. 


s = 0.8X. 


(90) 


116 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


Corner Reflectors (Angels) mating diffraction effects. Results are given 

The theory of the scattering by metallic objects here only for triangular-faced corner reflectors 
composed of two (“dihedral reflector”) and three (three faces, each an isosceles right triangle of 
(corner reflector) mutually perpendicular inter- leg length 1). The reflection from such a corner 



0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 

e 


Figure 25. Angular distribution of the response of Chaff (2 l/X = 2) . 



0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 

B 


Figure 26. Angular distribution of the response of Chaff (2 l/\ — 1.25) . 

secting planes was extensively developed. jg a superposition of reflections from a single 
Since in practice (see Section 12.2.1) the dimen- face, double reflections (using two faces), and 
sions are large compared to the wavelength, the triple reflections. The triple reflection pre- 
problem was treated by the methods of geomet- dominates when d > > \, which is the region 
rical optics. KirchhofPs theory was used in esti- of practical interest. 


TRANSMISSION AND REFLECTION OF ENERGY 


117 


The scattering by the corner reflector was 
shown to be given by that of a flat sheet whose 
area A is determined as follows. For a given 
direction of incidence, project both the corner 
and its image-in-itself on the wavefront of the 
incident wave. The overlapping portion of these 
two projections is the effective area A; the radar 
cross section is given by: 

a = 4ir I Y j 

Thus for a triangular-faced corner reflector, the 
maximum cross section (which is obtained when 


the cross section is decreased. If all three inter- 
section angles differ from 90 degrees by an 
amount e (in radians) , the decrease in cross section 
is 1, 3, and 10 db for Ze/X, equal to 0.20, 0.35, 
and 0.62, respectively. 

Anti-Window Device 

Because Window, properly sown, is effective 
in jamming radar systems, it was deemed im- 
portant to consider measures for reducing the 
effect of Window, so that the radar operator 
might obtain partial or complete information 



Figure 27. Cross section of Rope versus wavelength. Dash lines are limiting values for small and large 
arguments. 


the direction of incidence is the symmetry axis 
of the corner) becomes 

(93) 

For directions other than the symmetry axis, the 
value of a will decrease. If 6 is the deviation 
(in degrees) of the direction of incidence from 
the symmetry axis, an approximate value for 
the cross section is 

aid) = (Txnax (1 “ 0.00076(92)2. (94) 

The values of a given above are based on the 
assumption that the faces of the corner are 
mutually perpendicular. If the angle between 
any two of the faces deviates from 90 degrees. 


concerning his target. One such anti- Window 
system that was proposed utilized the difference 
between the fixed target echo and the random 
character of the Window return, for a single 
transmitted pulse. 

In general, a reduction in the pulse length re- 
sults in a proportional increase in the amount of 
Window necessary to screen a given target. 
(This holds exactly only when the target is small 
compared with the pulse length. For targets 
which extend over several pulse lengths— for 
example, a battleship — shortening the pulse does 
not change the amount of Window required for 
screening.) The proposed method would obtain 


118 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


the benefits of an effectively shorter pulse by 
means of a differentiator or some other suitable 
circuit, placed in the video stages of the receiver, 
to concentrate the target return into a pulse of 
duration short compared with the length of the 
transmitted pulse. 

Without the differentiator in the circuit, the 
resultant of all the retmms from a single trans- 



I 

I 

I 


SINGLE PULSE IN 
VIDEO, UNDIFFERENTIATED 


ECHO FROM DISPERSED 
WINDOW, IN VIDEO, 
SINGLE SWEEP, UN- 
DIFFERENTIATED 




Figure 28. Effect of video differentation on 
single pulse and on Window echo. (I, II, III, etc., 
refer to relative power content of designated 
signal.) 

mitted pulse appears on an oscilloscope as a 
rectangular target echo, accompanied by the 
sum of a great many rectangular Window echoes, 
very small in amplitude, from the individual 
Chaff dipoles. The Window return is spread out 
on the screen over many pulse lengths, whereas 
the target echo occupies only one. After dif- 
ferentiation, the target return is concentrated 
into two intervals shorter than the pulse length, 
one at each end of the original rectangular pulse. 
On the other hand, because the Window return 
(for dispersed Window) consists of the random 


superposition of the large number of small, over- 
lapping, dipole echoes, it remains spread out in 
range. Although the ratio of the power in the 
target echo (averaged over a pulse length or 
more) to that in the Window return does not 
change significantly, the fact that the target 
power is concentrated, while the Window power 
is not, increases the visibility of the target. The 
foregoing is illustrated in Figure 28. 

It should be emphasized that the differentiator 
acts independently on the return from each 
single pulse — that is, on each separate sweep of 
the oscilloscope beam across the screen. In a 
normal system, the amplitude of either a Window 
or target echo at a given range is seen to fluc- 
tuate strongly. These fluctuations occur at 
frequencies lower than the prf. They are the 
result of changes in the orientation and spacing 
of the Chaff dipoles relative to one another, or 
in the aspect of the target, between one trans- 
mitted pulse and another— in other words, from 
sweep to sweep. Thus the differentiator, which 
reacts independently to each sweep, does not 
affect the relative amplitude of such fluctuations. 

Mathematical Analysis. For the purpose of 
selecting a suitable criterion of visibility, the 
quantity A was defined as the ratio of the 
maximum of the target return, F(t)max, as it 
appears alone*^ on the oscilloscope screen, to the 
rms a-c amplitude (i. e., the root-mean a-c 
Window power in the video) of the Chaff dis- 
turbance, (Wa-c)*, as it appears alone on the 
scope: 


4 _ F{t) max 


(95) 


After differentiation the target echo has a 
maximum value 

RCE 

F(t) max ~ (^c sin Xc)) Xc — tOcT, (96) 

TTT 


where r is the duration of the original pulse, 
RC is a constant whose value depends on the 
differentiating circuit used, while fc is the half 
bandwidth of the i-f stages or the cutoff frequency 
of the video section of the receiver, whichever is 
the lesser. The quantity E is the video ampli- 
tude of the target return in the absence of 
Window. Figure 29 shows a typical pulse after 


^Actually, of course, there is receiver noise present as 
well, but its level is assumed negligibly low compared 
with the Window and target levels. 


TRANSMISSION AND REFLECTION OF ENERGY 


119 


differentiation. The rms a-c Window amplitude 
after differentiation was found to be 

(TF^c)* = {Xc - Si x,y, (97) 

T TT* 

sin X 

^1 Xc = J dX, 

where Eq is the rms amphtude of the a-c Window 
component, as seen in the video stages (or, 
equivalently, the square root of the a-c Window 
power) . 


Chaff package remains essentially a point source, 
i.e., for the first minute or two from the time it 
is dropped, the mean power spectrum was found 
to be 

11^«)(/) initial ~ 



Again the first term represents the a-c spectriun 
and the second, the d-c. Figure 30 illustrates 
equations (98) and (99), as well as the spectrum 



Figure 29. Time response of a differentiated square pulse. 


The total mean power spectrum in the steady 
state of complete dispersal was seen to be 

11 It' (/) steady state “ 


S El T 


sin X \ J_ 
X ) x~ 


— + 


, . ^ X . .,bx 
0 sin- — sin- — 


h = T / T, X — oiT = ^irfr, (98) 


where T is the radial spread of the Chaff cloud 
fmeasured in time units for two-way transmis- 
sion) . The first term of equation (98) represents 
the a-c (or high-frequency) power and the second, 
the ‘‘d-c” (or slowly fiuctuating) contribution to 
the spectrum. In the initial state, while the 


of the undifferentiated rectangular pulse, given 
by the following equation: 


Wp{f) = SFV 



( 100 ) 


The ratio A was then observed to take the form 
4 _ ^ I — \ — sin Xc 

“ 27r^ \ Eo I (Xc - Si Xc)^ 

_ Aq Xc — sin Xc 

27ri(:^:o-Sia:e)^^ ^ ^ 

where Aq is defined as the value of A for the 
unmodified receiver (i.e., without differentiator 
circuit), and is therefore A = E/Eq. Figure 31 
shows A as a function of cocT or/^r, in terms of Aq. 


120 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 



4 8 12 orr 16 20 24 28 


Figure 30. Window spectra, initially and after a condition of uniform dispersal. 



TRANSMISSION AND REFLECTION OF ENERGY 


121 


When Ao is known, it is a simple matter to obtain either A or Aq — that is, of the amount of Window 
cocT from the cin-ve for the appropriate value dropped. 

of A, The quantity A/Aq may be thought of as Summary of Results, The general results of 



the improvement produced by the differentiator, the analysis^^o are outlined below for the AJ 
or analogous circuits, and is seen to be independ- system against Window discussed above. The 
ent of the value of A required for visibility. It essential requirement is wide i-f and video band- 
is independent also of the absolute value of widths. In particular, it was found that: 



122 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


1. For short-pulse systems, where the pulse 
length r is of the order of 1 nsec or less, not much 
improvement can be obtained against Window, 
as the i-f and video filters cannot be spread to 
the necessary band widths. Widening as much 
as possible gives some improvement; but an in- 
crease, of say 25 per cent, in the amount of Win- 
dow dropped, over the minimum quantity effec- 
tive in jamming the unprotected set, probably 
destroys visibihty completely. 

2. For long-pulse systems, with r equal to 
3 Msec or more, considerable improvement is pos- 
sible within the practical range of design values. 
Improved, long-pulse sets may also take more 
than the minimum quantity of Window and still 
yield visible signals. For example, a lO-yusec 
system may be adjusted to “read through” twice 
the minimum amount of Chaff effective against 
the unprotected system. 

3. Against corner reflectors and Rope the 
method should be at least as effective as against 
Chaff. 

4. The cutoff frequency fc which must be used 
varies approximately as the square of the amount 
of Window dropped. An approximate formula 
for the above effect is 

/.r = 2(£y, /.r>3. 

The quantity Aq varies inversely as the quantity 
of Window dispersed. 

5. The frequency response of the optimum 
“composite” receiver Alter was determined and 
shown to represent an improvement of about 
1.41 to 1.5 in the ratio A/Ao over this ratio for 
a simple RC circuit alone. This corresponds to 
a gain of 3.0 to 3.5 db. A circuit having the 
approximate frequency characteristics of the 

theoretical) optimum filter was considered and 
also yields about 3-db improvement over the 
differentiator. However, because of the com- 
plexity of an optimum filter, an RC circuit may 
be more practical. An additional stage or two 
of amplification is probably necessary in either 
case. 

6. Single differentiation, in the video ampli- 
fier, is more effective than multiple differentia- 
tion. 

7. When any of these circuits is used there is 
a loss in range, because the i-f stages are mis- 
matched and because thermal noise is generated 


in the mixer. When is eight times its normal, 
matched value, the effective range in the absence 
of Window is reduced 25 per cent. As more 
Chaff is dropped, if the cutoff frequency is cor- 
respondingly increased, the reduction in range 
also increases. 

8. The AJ measure is also apphcable against 
narrow-band noise jamming, where the noise 
spectrum is narrower than either the original i-f 
or video bands of the receiver. The systems 
fail badly when the noise is wider than the 
bandwidth of the unadjusted i-f and video stages. 

9. The method is designed for type A pre- 
sentation. It is not nearly so effective in systems 
which have limiting, particularly sets employing 
a plan-position indicator [PPI] display. 

Frequency Sensitivity of Complex Targets 

A brief theoretical analysis®^° was carried out 
on the fluctuations of the echo from complex 
targets produced by small changes in the carrier 
frequency of the incident wave. The targets 
considered were those composed of two or more 
reflectors spaced a number of wavelengths apart. 
This investigation was begun in connection with 
the proposal to use frequency modulation of a 
carrier in order to distinguish large, complex 
targets, such as ships, from radar decoys or other 
similar reflectors of small physical size. 

It was found that, when a radar echo is made 
up of the sum of a large number of separate 
reflections whose phases vary in a random manner 
relative to the transmitter, the amplitude of the 
resultant echo fluctuates according to the Ray- 
leigh amplitude-distribution law. If the number 
of separate reflectors is small, the resultant return 
stiU obeys the Rayleigh law provided that each 
individual echo follows that distribution. In 
addition, the problem of two reflectors was dealt 
with, in the case where the echo amplitudes from 
the reflectors are equal and constant but where 
the relative phases vary at random. 

The results of this study are shown in Figures 
32 and 33. The former illustrates the proba- 
bility distribution of echo amplitudes (relative 
to the rms amplitude) when any number of 
reflectors are involved, each with random phase 
and Rayleigh distribution of amplitude. This 
figure also shows the probability curve of ampli- 
tude from the two equal reflectors whose relative 
phase alone varies. Figure 33 shows the proba- 


TRANSMISSION AND REFLECTION OF ENERGY 


123 


bility distribution of the difference between any 
two amplitude measurements made at random 
times for the two cases described above. These 
latter curves are seen to be extremely similar 
despite the difference between the curves of 
Figure 32; thus, the two types of targets should 
behave in the same manner under frequency 
modulation and give equally rehable complexity 
indication. It was concluded, therefore, that the 



0 .2 .4 .6 .8 1.0 1.2 l.i* 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 

AMPLITUDE RELATIVE TO RMS AMPLITUDE (a) 


Figure 32. Probability distribution of ampli- 
tudes from multiple reflectors. 

exact nature of the target was of little importance 
as long as it was complex in nature. To a large 
extent this conclusion was confirmed by experi- 
mental investigations.®®® 


eluding those concerned with antennas for 
search receivers), studies of propagation prob- 
lems, an analysis of the theory of radar echoes 
from ship targets, and studies of the radar cross 
sections of both airplanes and ships. 

Theoretical Antenna Studies 

In all RCM work, or for that matter in all 
radar or communication problems, antennas ulti- 
mately play a part, in both the receiving and 
transmitting aspects of radar and RCM prob- 
lems. Theoretical studies of various kinds were 
undertaken to determine the radiating properties 
and other important characteristics of some of 
the antennas used in RCM. 



0.0 0.2 O.H 0.6 0.8 1.0 1.2 I.*! 1.6 1.8 

DIFFERENCE (/S) BETWEEN TWO RANDOMLY SELECTED VALUES OF THE 
RELATIVE AMPLITUDE OF THE ECHO FROM A COMPLEX TARGET WITH 
VARYING ASPECT 

Figure 33. Probability distribution of ampli- 
tude differences. 


^ Radiation and Propagation of 
Radio Waves 

Much of the theoretical work carried out in 
the course of the RCM program dealt with the 
radiation, propagation, and reflection of radio 
waves. Among such investigations were several 
theoretical studies of antenna problems (in- 


General Antenna Problems. In this latter con- 
nection an investigation of the equivalent radius 
of thin cylindrical antennas was undertaken. 

It was shown that, for a cylindrical antenna (or 
scatterer — see Section 6.3.1), whose linear cross- 
sectional dimensions are small compared to both 
the length of the cylinder and the wavelength X, 
the form of the current distribution over the 
cross section can be determined independently 


124 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


from the solution for the variation of the total 
current along the length. When this result is 
apphed, for example, to the Rope problem^^^ 
(Section 6.3.1), one finds that from any solution 
of the antenna problem for a thin, circular 


is an eUipse of semimajor axis h and semiminor 
axis lib, then the solution of an antenna problem 
for the circular cylinder can be applied to the 

elliptic cylinder by replacing a by ^ (1 + /x). 



V 


RHOMBUS 


® A > 

IRREGULAR HEXAGON 

t 




cyhnder of length Z, one can obtain a solution 
for a flat strip of length I and width s by replacing 
a, the radius of the cylinder, by s/4 in all formu- 
las. Moreover, if the cross section of the cylinder 


Another brief study was made on the “equiva- 
lent point’’ antenna, of constant-current epoch. 
The idea of equivalent point antennas is inherent 
in the method of analysis, whose purpose was 


TRANSMISSION AND REFLECTION OF ENERGY 


125 


the calculation of the Poynting flux at a remote 
point. A physical interpretation of such a cal- 
culation is that the infinitesimal parts of the 
antenna have all been translated, with appro- 
priate changes of phase, to a chosen origin where 
together they constitute an infinitesimal radiator 
whose current moment generally depends in mag- 
nitude and phase on the direction from which 
it is viewed. While it was previously recognized 
that the origin could be chosen anywhere near 
the antenna, there was an impression that some 
unique point exists which may be regarded as a 
kind of centroid of the radiating current elements, 
and there was speculation about whether such 
points exist for all antennas. 

A criterion whereby the existence of such 
preferred points may be recognized was found — 
namely, that the most desirable choice of origin 
is that for which the current phase of the equiva- 
lent point radiator is independent of direction. 
These points, however, do not always exist. For 
example, in the case of the quarter-wave resonant 
section, such a point cannot be found. It is 
sometimes possible, by replacing finite segments 
with equivalent points (when they are specifi- 
able) , to simplify the reasoning and computation 
whereby the properties of the whole antenna are 
obtained. The greatest simplification is achieved 
when the current moments of the equivalent 
points of all segments are directed along the same 
hne and are equal in magnitude and phase. 
Specific calculations were carried out for a num- 
ber of simple, illustrative examples. 

Loop Antennas. An examination of means for 
determining the radiation characteristic of an- 
tennas in the form of large polygonal loops was 
also considered.^^^ The following definitions are 
helpful in stating the principal result: 

X = wavelength in air; 

/3 = 27r/X; 

r = distance from equivalent point source; 
d = polar distance measured from normal to 
loop; 

0 = longitude measured from an arbitrary line; 
/o = amphtude of the current; 

1 = complex current; 

dfi = element of solid angle; 

E = complex electric intensity (distant field); 
H = complex magnetic intensity (distant field); 
F = equivalent current moment; 

«I> = mean power radiated per unit sohd angle; 


R = radiation resistance; 

d = directivity defined as space averaged- 

^ -Zme-'^Q^Fe. 

= , 

(102a) 




= 


47rr 


(102b) 


II ’ (102c) 

, 47r<I> 

The general antenna is shown in Figure 34. For 
the whole polygon the components of the equiva- 
lent current moments are 


Fq = 2ilm cos d Ci 


sin Uj 


i = 1 Ui 


sin 1^ cos ■ + |Si 1 1 — di J J 


(103a) 

cos {ai — 0), 


^ o r Sin Wi 

F — 2ll m / > Ci 


i — 1 Ui 


Sin 


(103b) 

1^ ^Qfi cos a, ■ + i3i ^ I — d,- j J sin {ai — </>) , 


where I m refers to the current measured in the 
middle of the chain of n sides, and o- is the sum 
of the lengths of the n sides. Here di is the 
distance along the wire from the generator to 
the middle of the ith side, r, is the radius to the 
middle point of the ith side, and ai is the angle 
between this vector and the direction of the field 
point. The quantities Ui are given by Ci/2 
(jSi — jSo cos i/'J, where now is the angle 
between the direction of the ith. side and that 
of the field point, and Ci is the length of side i. 
The subscript “0” is used for waves in air and 
‘T’’ for waves along the wire. 

The general expression, equations (103), take 
different and generally simpler forms in a number 
of important special cases.^ For a circle with a 


^The regular polygon with traveling waves or with a 
uniform current distribution is not considered here; the 
reader is referred to page 6 of reference 475. 


126 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


uniform current and radius a we have 
F 0 = 2TriIaJi {^oa sin 6), 

Fe = 0 , 

and (jSo = jS) here, 

^ (/3a sin 6 ) ; 

_ 2Jl (jgg sin 6) 

J2 (y) dy 

r2^a 

R = GOtt- jSa J J2 (y) dy, 

where Ji is the familiar Bessel function of the 
first kind, first order. For the radiation resistance 
in this case, see Figure 35. Calculations showed 
that at moderate frequencies polygons with uni- 
form current have nearly the same properties 
as circles. 

For the square with uniform current the fol- 
lowing results were obtained: 

Fe = 0 ; 

^ , sin wi sin 1/2 

Fa, = il^c- sin 6 • , (105a) 

^ Wi 1/2 

^ 15 ^,T 2 . o n / sin ui sin 1/2 \ 

= • — j, ( 10 .b) 

where Ui = M/3c sin 6 sin {(f) — 7r/4) and 
U 2 = 34 /3c sin 0 cos (</> — 7r /4); here c is the 
length of a side, as before. 

For a rhombus with travehng waves it was 
found that 


(104a) 


(104b) 


^ T ^ o « • • , Sin Ui Sin a2 N 

Fe = — 2i/m/8c-cos 0sin(/)Sin A , (106a) 

Ui U 2 

F^ = —2ilm jSc" sin A (cos cf) — sin 6 cos A)* 
sin Ui sin U 2 


III 


U2 


60 


4> = — jS-c^/o sin- A 


sin- Ui sin- U 2 


u: 


ul 


(106b) 

(106c) 


where now ih = 3 ^ 2 /3c [1 — sin 6 cos (A + </>)] 
and U 2 = 34/3c [1 — sin 6 cos (A — </>)], and A 
is the longitude of the first side. The formulas 
for F do not appear to have been given previously 
in a concise form. Other possibilities were con- 
sidered, such as the irregular hexagon with 
traveling waves, and with symmetry with respect 
to rectangular axes, one of which is the initial line 
0=0. Loops with standing waves and the 
problem of driving large loops with uniform cur- 
rent were also examined, as well as possible ap- 
plications of these various antennas to problems 
of direction finding. 

Search Receiver Antennas. Much of the theo- 


retical work on antennas was concerned with 
the search receiver problem, of which the opti- 
mum conditions for finding and observing enemy 
signals (primarily radar) is the principal question. 

One study dealt with the use of continuously 
rotating direction finders against signals of vary- 
ing intensity. When such direction finders, 
having azimuthal scope presentation, are used 
to locate rotating beam transmitters, the varia- 
tion of the field strength at the receiver causes 
each curve drawn on the scope to indicate a false 
direction. There appeared to be two ways to 
overcome the difficulty: (1) If the receiving 
antenna is rotated at such high speed that a 
considerable number of curves are drawn on the 
scope for one turn of the transmitter, the largest 
curve of the group of curves gives a good indi- 
cation of the desired direction. There are a 
limited number of slow-speed ranges which give 
as good a result, but these lack the advantages 
of persistence on the screen. (2) If two direction- 
finding antennas, whose directivity diagrams are 
mirror images of each other, are caused to rotate 
at equal speeds in opposite directions, they may 
be adjusted in relative angle so that their out- 
puts cause identical curves to be traced on the 
scope. The true direction then bisects the angle 
between the two indicated false directions. 
Apparatus which cannot be run at high speed 
should be run either at nearly one-to-one, or 
else so slowly that the required number of curves 
are drawn during one turn of the receiver an- 
tenna. In the latter case, a group of curves 
closely resembles a set of radial lines equally 
spaced in angle. 

A further study was carried out on the opti- 
mum directivity pattern for search antennas.®®® 
Because airborne search antennas must be small, 
the area within which radar transmitters may be 
detected is correspondingly limited. The search 
airplane is accompanied in flight by a closed 
curve which has the property that, if a certain 
radar is within it, the signal can always be 
observed, provided the receiver is “illuminated’^ 
and properly tuned. The radius of this antenna 
curve is proportional to the square root of the 
power directivity of the receiving antenna. In 
order to scout as rapidly as possible, it is desirable 
to have the antenna curve extend sidewise as 
far as the horizon permits. Requirements for 
direction finding are better satisfied if the antenna 


TRANSMISSION AND REFLECTION OF ENERGY 


127 


curves slant forward to some extent. The 
amount of sidewise gain that can be used is 
hmited by the fact that increased gain implies a 
shorter interval of time which the radar spends 
within the curve. This time interval determines 
the chance of a concurrence of illumination by 
the radar and proper tuning of the receiver. 
Supposing that a minimum acceptable proba- 
bihty of detection has been chosen, it is found 
that the fore-and-aft distance across the antenna 
curve should be uniform and not less than that 
which corresponds to the acceptable probability. 


the power or distance required to lay down a 
field sufficient to jam reception. Jamming is 
almost invariably done by means of ground-wave 
transmission, since ionospheric conditions limit 
the frequencies which can be used for sky-wave 
transmission over a given jamming distance to 
such an extent that sky-wave jamming is gen- 
erally unprofitable. The propagation informa- 
tion gathered was therefore confined to ground 
waves. 

The variation of ground-wave field intensity 
with distance depends on several factors, among 



Figure 35. Radiation resistance, circular loop antenna as function of radius. 


In order to detect radars which lie nearly in 
the track of the search plane there should also 
be a forward lobe extending beyond the distance 
at which the enemy operator will probably shut 
off* his radar. The extent of this lobe also depends 
on the probability involved. 

Propagation Studies 

In developing a jamming system or in solving 
a specific jamming problem, a knowledge of the 
propagation of radio waves is essential, in order 
to estimate the field intensity which the enemy 
is dehvering to his receiver and then to determine 


which are frequency, polarization, antenna ele- 
vations, and type of terrain — that is, whether 
the radio path is over sea or land and whether 
the land is fiat or mountainous, jungle or rela- 
tively open. Although a considerable amount of 
information had been published on radio propa- 
gation, the need to organize this material in a 
more usable form for rapid reference was recog- 
nized early in the RCM program. The most 
recent compilation of such information is Issue 3 
of the handbook Propagation Curves , compiled 
by the Bell Telephone Laboratories, Inc. (under 
contract OEMsr-966) . This handbook super- 
sedes similar information previously given in 


128 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


earlier reports^®’ and handbooks. Another 
study of ground-wave propagation®^ was carried 
out by the Radio Corporation of America (under 
contract OEMsr-895). 

The material in the latest handbook^^® is in 
the form of curves which can be used to estimate 
the received field intensity of ground-wave sig- 
nals when they are being transmitted (1) between 
an aircraft and a ground station, (2) from one 
aircraft to another, and (3) from one ground 
station to another ground station, at frequencies 
from 200 kc to 600 me. The information covers 
air-plan elevations as high as 40,000 ft and dis- 
tances up to 500 (statute) miles, for both hori- 
zontal and vertical polarization and for three 
types of ground conditions: namely, sea water, 
good soil, and poor soil. In addition to revisions 
of the earlier curves, the handbook contains an 
explanatory text, and includes curves for evalu- 
ating the effects of antenna elevation, a nomo- 
gram for estimating “shadow losses” caused by 
hills, and a brief statement on tree losses. This 
handbook provides reference material of use in 
estimating not only jamming performance but 
radio communication performance as well, and 
therefore has wide application. 

These curves served to illustrate the tremen- 
dous advantage of an airborne jammer over a 
ground-based jammer, brought about by the 
higher antenna elevation. Since airborne jam- 
mers can also be carried much closer to the 
target, more effort was accordingly directed 
toward developing airborne jamming than to- 
ward similar developments for ground-based 
jamming. Future work on wave propagation 
involves consideration of higher frequencies 
which may come into more common usage and 
augmentation of the present data (which are 
based on the assumption of standard propagation 
conditions) with whatever information becomes 
available on the effects of special conditions in 
the lower atmosphere. 

Analysis of Ship Echoes 

The foregoing propagation studies (as well as 
others) were of considerable use in an analysis^^^ 
of the echoes from ships and other naval targets. 
This study was concerned with the formulation 
of a theory to permit the approximate calculation 
of the power density of radar echoes returned 


from naval targets and the computation of jam- 
ming powers and minimum jamming distances 
in naval operations. For normal propagation 
conditions, formulas were developed to permit 
such computation at distances within the radar 
horizon. The conditions for maximum effective- 
ness of a given jammer were analyzed and the 
practicability of various available jammers was 
evaluated. 

Parameters and Formulas. The estimation of 
radar echoes from ship targets is essentially more 
difficult than the parallel problem for aircraft. 
The difference is accounted for by three factors: 
(1) reflection from the sea, which produces inter- 
ference patterns exhibiting a rapid variation of 
field strength with height; (2) the increased 
extension of the target, which allows it to inter- 
cept several lobes of a nearby radar; and (3) the 
increased complexity of the reflecting surfaces, 
which results in a larger fluctuation in return 
than is experienced with an airplane. In the 
case of the airplane, although the dependence on 
aspect and frequency cannot be eliminated, the 
problem was partially solved by the introduction 
of an effective cross section, determined experi- 
mentally. This method was practical because 
the parameter as defined is independent of the 
distance at which it is measured — a consequence 
of the fact that at any distance the power density 
incident upon the airplane is essentially constant 
across the surface of the target. 

In the naval case the presence of an extended 
conducting surface, the sea, causes the field 
strength across the ship to vary rapidly with 
height. This new element in the problem makes 
it necessary to distinguish two zones, in order to 
reduce as much as possible the variation of the 
reflection parameter with distance. In the first 
of these regions, the one closest to the radar 
installation, the echo power density is given in 
terms of an effective cross section whose dimen- 
sions are length squared, as in the case of an 
airplane; because of this similarity, the region 
was called the “Air-zone.” At larger distances, 
the ship was said to be in the “Sea-zone.” In 
this region, the echo power density is attenuated 
as the eighth power of the radar-to-target sepa- 
ration, and the echo parameter used is a constant 
whose dimensions are length to the sixth power. 
This region was the one most commonly en- 
countered in operations involving the jammers 


TRANSMISSION AND REFLECTION OF ENERGY 


129 


available during World War II. In the Sea-zone, 
the echo power density displays a very strong 
dependence upon the height of the radar antenna 
and upon the frequency; this dependence is not 
observed in the Air-zone. 

All the foregoing was derived on the assump- 
tion of a plane, perfectly conducting earth, and a 
normal atmosphere. The plane earth assump- 
tion is sufficiently accurate in distances up to 
two-thirds of the radar horizon (or perhaps 
farther), whereas the assumption of a perfect 
conductor is applicable to sea water in the most 
practical case of horizontal polarization. At 
larger distances, it is necessary to consider a 
third zone, in which the curvature of the earth 
and ultimately the diffracted ray play a part. 
In this region, a general solution to the problem 
becomes almost impossibly complex, but an 
approximate solution was derived which ex- 
tended the useful range of the analysis as far as 
the radar horizon, with reasonable accuracy. 

Formulas were derived^^^ for the echo power 
density, the minimum screening range for a 
jammer of known power, and the power required 
to jam to a given range. When the target is 
well into the Sea-zone, the minimum jamming 
distance is proportional to the fourth root of the 
ratio of the effective radar power to the effective 
jammer power; to the square root of the ratio of 
radar antenna height to jammer antenna height; 
to the square root of the frequency; and to the 
fourth root of the Sea-zone reflection parameter. 
In the Air-zone the dependence of the minimum 
jamming distance on radar and jammer param- 
eters is more complicated, but under most 
conditions the proportionality is roughly the 
square of that hsted for the Sea-zone case. 

Under many conditions, the solution for the 
minimum jamming distance could not be written 
expHcitly; but graphical solutions were devised 
and curves were drawn to permit the rapid cal- 
culation of the minimum range. 

Operational Considerations. On the basis of 
the equations discussed above, the minimum 
jamming distance was calculated for a variety 
of operational situations with the jammer on 
the target vessel. Such calculations were per- 
formed for a wide range of ship sizes, for several 
frequencies, and for both low-power and high- 
power jammers. Although the computations 
were carried out for the purpose of illustrating 


the techniques of calculation developed, the re- 
sults shed considerable light upon the usefulness 
of various types of jammers. 

Consideration was given to the question of 
screening a ship with a jammer carried on an 
airplane. It was concluded that, if a given 
jammer and antenna are installed on an aircraft, 
their effectiveness in screening a ship is at least 
as great as the effectiveness of the same jammer 
and antenna carried on the ship itself, and often 
greater — provided that the most effective use is 
made of the jammer in both arrangements. (In 
some cases, especially in small ranges, it is im- 
practicable to use an airborne jammer in the 
most effective way.) On the other hand, it is 
frequently possible to carry a much larger jam- 
mer and a much higher-gain antenna on a ship 
than on aircraft. 

A short study was made of the use of Chaff or 
other forms of Window to simulate or screen 
surface vessels. It was concluded that, except 
at very great ranges or for very small ships, the 
amount of Chaff required for these purposes 

made its use impracticable. 

Equations were derived for the optimum 
height of the jammer antenna, both for ‘‘off- 
target” jamming (when the jammer is not carried 
on the target vessel) and for the self-screening 
case (when it is). These formulas showed that, 
although it is generally desirable to place a jam- 
ming antenna as high as possible on a ship, this 
is not always the case. For really powerful 
jammers, the exact height of the antenna may 
be of considerable importance. With low-power 
jammers, however, the minimum jamming dis- 
tance is almost always in the Sea-zone; and in 
this case the higher the antenna, the more 
effective is the jamming. 

Derivation of Equations. Two different deriva- 
tions were carried out for the basic equations of 
the analysis. The first employed a number of 
simpHfying assumptions in an attempt to show 
briefly the physical reasons for the results gained. 
The equations were also derived in as rigorous a 
way as was possible; although this derivation is 
far from exact, the theory is in such a form that 
any errors are minimized. The “rigorous” de- 
rivation showed that the results of the simpler 
one were somewhat more accurate than one 
might conclude from the simplicity of the assump- 
tions used.^^2 


130 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


Analysis of Radar Cross Sections 

In order to perform the actual computation of 
minimum jamming distances and other quanti- 
ties of interest, experimental figures on the 
reflection parameters (radar cross sections) were 
required. It was found that the raw experi- 
mental data could not be used directly but had 
to be studied and averaged in order to be of use. 


compiled by averaging the parameters over all 
frequencies. It was felt that the wide scattering 
of the original figures provided sufficient weight- 
ing to the abnormally large values of the param- 
eters so that the averages tabulated were amply 
conservative — too large rather than too small. 

As further data became available in reasonable 
quantities, the same procedure was followed. On 
the basis of these additional results, the original 



Figure 36. Average radar cross section per aircraft in formation, horizontal aspect. 


Ship Cross Sections. A very large amount of 
experimental data on radar reflections from ships 
was analyzed, in connection with the study of 
ship echoes, and values of the Sea-zone and Air- 
zone reflection parameters were thus calculated 
for a variety of different ships. The results of 
these calculations were tabulated, and revisions 
were made as additional data became available. 

It was thought desirable to list parameters 
which would be widely applicable over a class of 
ships and a variety of frequencies and still not 
be cumbersome. For this reason, and because 
of the uncertainty as to the precise accuracy and 
generalized vahdity of the data, the tables were 


figures were revised. (It was generally found 
that the original values were too large.) The 
revised tables were turned over to the Navy but 
were never published or distributed generally. 

Airplane Cross Sections. Measurements were 
made by the Ohio State University Research 
Foundation of the radar cross sections of air- 
craft; the experiments were performed on scale 
models of the airplanes for a variety of frequen- 
cies (see Section 6.5). These data were analyzed 
and averaged, so that they could be apphed to 
operational problems. 

The comphcated lobe structure of the reflection 
patterns from the airplanes, as measured experi- 


TRANSMISSION AND REFLECTION OF ENERGY 


131 


mentally, indicated that some procedure for 
smoothing the data would be required before 
they could be put to practical use. Methods 
were developed for this purpose, as well as for 
using the results in various operational applica- 
tions. The dependence of the airplane cross 
sections on polarization and frequency was in- 
vestigated. It was found that measurements on 
vertical and horizontal polarizations alone were 
insufficient to enable the prediction of the re- 


dealt with the properties of lines and guides as 
used for the transmission of r-f energy; the large 
majority of the investigations, however, were 
concerned with various apphcations of the 
impedance-transforming properties possessed by 
sections of transmission line. 

Such sections of line were used, singly or in 
combination, in a variety of ways: as resonant 
systems or component parts thereof, as trans- 
formers to match impedances, or in the construc- 



20 ^0 60 80 100 120 IHO 160 180 


4>o 

Figure 37. Average radar cross section per aircraft in formation, from below. 


sponse on intermediate polarizations. It was 
noted also that the smoothing procedure used 
increases in validity with increasing frequency. 

The averaging process was carried out, and the 
results plotted and tabulated, for all the various 
measurements available from Ohio State Uni- 
versity. Figures 36 and 37 show typical curves 
resulting from the analysis. 

Transmission Lines and Wave Guides 

The properties of transmission lines and wave 
guides received a considerable amount of theo- 
retical attention. Some of the theoretical studies 


tion of filters. In considering these applications 
of line sections, it should be remembered that the 
equations for the impedance looking into a sec- 
tion of the transmission line are the same as those 
for a section of wave guide. A great many of the 
theoretical results summarized in the following 
paragraphs, therefore, could be applied equally 
well to sections of wave guide, even though they 
were derived originally for transmission lines. 

Properties of Lines and Guides 

As stated above, several studies were made of 
the general properties of transmission fines and 
wave guides. One of these dealt with the char- 



132 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


acteristic impedance of a shielded, balanced 
transmission line, composed of two inner con- 
ductors S3mimetrically placed within a cylindrical 
shield .^®2 A comparison was made between three 
formulas for this characteristic impedance, and 
expressions were derived for the errors in them. 
The formulas were taken from various sources, 
two of them from the German hterature. 

Velocity of Propagation in Coaxial Line. A 
theoretical investigation was made of the group 
velocity of electromagnetic waves in a coaxial 
hne. If there is resistance in the conductors 
composing the hne, a correction term must be 
introduced into the equation for the velocity. 
The iisual expression for this correction term does 
not include the result of the change in self-induct- 
ance produced by the skin effect which accom- 
panies the resistance. Expressions for the com- 
plete correction term were therefore derived,^^^ 
and it was shown that the skin effect correction 
is normally considerably larger than the term 
which is usually included. 

Ridge Wave Guide. A study was made of a 
rectangular wave guide having a rectangular 
ridge projecting inward from one or both sides. 
Equations were derived for the cutoff frequency 
and the characteristic impedance of such a wave 
guide, and curves for these quantities were drawn 
for the various transmission modes. It was 
shown that ridge wave guide has a lower cutoff 
frequency and characteristic impedance and 
greater higher-mode separation than a simple 
rectangular wave guide of the same width and 
height. The equation for the cutoff frequency is 
fairly accurate for any practical cross section. 
The impedance equation is strictly accurate only 
for an extremely thin cross section. Values cal- 
culated by the use of this equation, however, 
were found to check experimental values very 
closely. A variety of different applications for 
such a guide were investigated.®®^’ ^^7 

Resonant Circuits and Systems 

A number of studies were carried out on the 
general properties of resonant systems and of 
sections of transmission hues used as resonant 
circuits, as well as applications of such systems. 
As suggested previously, the results for hne sec- 
tions could be apphed to wave guides also. 

Analysis of Resonant Systems. An analysis 
was made of resonant systems for ultrahigh 


frequency from the point of view of external 
impedance measurements.®®® Resonant systems 
in the form of four-terminal networks are mainly 
used as band-pass filters and impedance-matching 
transformers. In a tank circuit of a vacuum-tube 
oscillator or amphfier, these functions are com- 
bined, and the analysis was performed with this 
application in mind (although its scope can easily 
be extended). 

Most of the resonant systems used at ultra- 
high frequency have more than one resonant 
mode, and each mode of a fom-terminal system 
has a complete set of at least five parameters 
which are independent in the sense that none of 
them can be determined from known values of 
the other four. Direct measurements are often 
difficult or impossible — for instance, in distri- 
buted-constant systems or in vacuum tubes 
where the resonant system is enclosed in the 
evacuated shell. If an equivalent circuit in 
terms of lumped constants can be found, how- 
ever, the relations between the parameters and 
the “cold” impedance seen from the output ter- 
minals are easily derived; the parameters can 
then be determined by standing-wave measure- 
ments. The equations for the calculation of 
approximately equivalent circuits for common 
resonant systems were studied on the basis of 
accuracy and simplicity of analysis. Experi- 
mental procedure and sources of error in im- 
pedance measurements by standing-wave deter- 
minations were investigated briefly, and a 
number of methods were set up for calculating 
the parameters of the resonant systems from 
standing-wave data, with the aid of graphs and 
simple formulas. 

Resonant-Line Sections. If a section of trans- 
mission line is short-circuited at one end and 
terminated at the other end in a reactance, a 
load resistance, and a power source, the section 
will resonate with the terminating reactance; 
and such an arrangement is often used as a 
resonant circuit at high frequencies. If the 
terminating impedance and source are in series 
across the end of the section it acts as a series 
resonant circuit, whereas if these elements are in 
parallel across the section it behaves like a 
parallel resonant circuit. 

Equations were derived for the frequency 
bandwidth of such a resonant section for both 
series and parallel resonance. Two special 


TRANSMISSION AND REFLECTION OF ENERGY 


133 


cases were considered: (1) the loaded section, 
where the load resistance is of such a size that it 
receives almost all the power; and (2) the 
unloaded section, where the size of the load 
resistance is such that all but a neghgible fraction 
of the power is dehvered to the section. The form 
of the equations is such that they apply to either 
an inductive or capacitive termination. 

The condition for resonance was found: 
namely, that the reactance looking into the 
shorted section without the termination be equal 
and opposite to the terminating reactance. It 
was shown that there was a series of values for 
the angular length of the line which satisfy this 
resonance condition; these values are known as 
the modes of resonance. Equations were derived 
giving the change in frequency band produced 
by a shift in the mode of resonance, for all the 
cases mentioned above — that is, series and paral- 
lel resonance, and loaded and unloaded sections. 
Since the angular length of the section is propor- 
tional to the product of its physical length and 
the frequency, the mode of resonance may be 
shifted by changing either the length of the 
frequency; both methods of shifting modes were 
considered.^^^ 

Mode Separation in an Oscillator. A common 
type of h-f oscillator uses two sections of coaxial 
transmission line as resonant circuits, of the type 
discussed above. One of these sections maybe 
considered to determine the frequency of oscil- 
lation in accordance with the resonance condition 
and, of course, a number of different modes are 
possible. The adjustment of the other section 
may then be considered to determine at which of 
these possible frequencies the apparatus actually 
oscillates. The difference in the physical lengths 
of the second section for the two modes under 
consideration is known as the mode separation, 
and it is important that this separation be as 
large as possible to prevent the oscillator from 
producing more than one frequency. 

The problem of separating the first and third 
modes of oscillation in a coaxial oscillator of this 
type was considered. The equations involved 
could not be solved directly, but a comparatively 
simple graphical solution was found. It was 
shown that the mode separation increases with 
the difference between the product of the ter- 
minating capacity and the characteristic im- 
pedance for the two sections. In addition, it was 


concluded that the mode separation varies quite 
slowly as a function of resonant frequency. 

Design of Matching Transformers 

An extensive investigation was carried out on 
the design and performance of matching trans- 
formers designed to cover wide frequency bands 
and composed of sections of transmission lines 
(or wave guide) . The early work was concerned 
chiefly with a study of the behavior of matching 
sections of known types over a wide range of 
frequencies. The later work dealt largely with 
methods of choosing the combination of sections 
in the transformer and the values of the section 
parameters in such a way that the character- 
istics of the transformer would compensate for 
any mismatching in the load over the frequency 
range to be covered. 

Performance of Matching Sections. Methods 
were found for determining the frequency char- 
acteristics of various specific types of matching 
transformers made of sections of hne in series. 
Equations were derived and diagrams drawn for 
a single quarter-wave section and for a pair of 
such sections. It was shown, for instance, that 
a quarter-wave section matching a constant re- 
sistance load has a frequency band considerably 
wider than is generally reahzed, and that two 
paired quarter-wave sections give an even wider 
band. The use of a relatively new section for 
matching the load at two frequencies was ana- 
lyzed, as well as the tuned-circuit equivalents 
of this section. 

Ideal Load. At this stage, the concept of 
“ideal” or “matching” load was introduced. 
The ideal load is defined for a particular section 
or transformer as that load which, applied at 
one end of the section, maintains perfect match- 
ing at the other end at any frequency; in other 
words, the ideal load for a section at one pair of 
terminals is the conjugate of the load looking in 
the direction of the opposite pair, when the im- 
pedance to which the load is to be matched is 
connected at this second pair of terminals. 

This concept was found to be of the greatest 
assistance. Once the ideal load has been cal- 
culated for a large variety of types of trans- 
formers, a matching transformer can be designed 
simply by choosing the one whose ideal load is 
most similar to the actual load to be matched. 
Such calculations were performed in great detail 


134 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


for a matching transformer composed of a single 
section of line, and charts were drawn from which 
it is possible to determine by inspection the fre- 
quency limits of a given load and single-section 
transformer (assuming a limit of 17 per cent on 
the reflection coefficient). A simple formula for 
finding the complete frequency characteristics in 
terms of the ideal load was also derived 


I K 1^ 


{R - RraY + (A - 

(R + RmY + (V - XmT ^ ^ 


Here R + jX is the actual load, Rm jXm the 
ideal load, and \K\ the modulus of the reflection 
coefficient. 

Series of Quarter- and Half-Wave Sections. For 
all except the simplest types of matching trans- 
formers composed of sections of transmission 
lines, the expression for the ideal load becomes 
too complicated to be handled analytically (the 
same is true for other methods of approach to 
the matching problem). In order to have avail- 
able a reasonable number of transformer param- 
eters whose values could be adjusted suitably, 
the idea was suggested of using a series of line 
sections of equal length. Upon further investiga- 
tion, it was found that, for more than two sec- 
tions, even this arrangement could be handled 
only when the lengths of the sections were close 
to a quarter or a half wavelength. 

In this case, however, the expressions, although 
complicated, could be handled algebraically. 
Equations were derived, therefore, for the ideal 
load of such a series of sections, and the arrange- 
ment was found to be an extremely powerful 
tool. Instead of writing the expressions for the 
ideal load as a function of frequency in the 
region where the sections were quarter-wave or 
half-wave long, the equations were written in 
terms of the ideal load and its derivatives at the 
central (resonant) frequency. In this form the 
equations were found to be somewhat more flex- 
ible in their application. 

It was possible to write expressions for all 
transformers where the number of sections was 
not greater than four. In some cases, however, 
the equation could not be solved explicitly for 
the parameters of the transformer — that is, for 
the characteristic impedances of the sections. 
Graphical solutions were therefore constructed 
for transformers of this type. 

Many other approaches to the general problem 


of designing matching transformers were investi- 
gated, and several other possible combinations 
of sections were considered, but the foregoing 
method appeared to be the most fruitful and 
therefore received the greatest attention. 

Synthesis of Matching Sections. The problem 
of synthesizing broad-band matching transform- 
ers also received a certain amount of atten- 
tion^^»“^ at the Radio Corporation of America 
(under contract OEMsr-895). Consideration 
was given to the problem of choosing a single 
section of line in such a way as to match an 
arbitrary load over the widest possible range of 
frequencies,^^ and design charts were constructed 
for the synthesis of some simple two-element 
broad-band matching transformers. In general, 
the approach used was similar to that just 
described. 

Wide- Band Balancing Transformer. On the 
basis of the work discussed above, the frequency 
characteristics of a particular type of balun (a 
transformer from an unbalanced to a balanced 
line) was investigated. It was found that by 
designing the balun properly and by inserting a 
properly designed pair of quarter-wave sections 
to match the balun to a balanced line of higher 
characteristic impedance, the standing- wave ratio 
could be kept below 1.25 over frequency bands 
of the order of four to one. Combination match- 
ing and balancing transformers of this type were 
designed and the values of the parameters cal- 
culated for the transformation from a 50-ohm 
unbalanced line to a 128-ohm and a 150-ohm 
balanced line. 

Broad-hand Wave Guide-to-Line Junction. In 
the design of microwave filters and receiver 
transmission systems, there was required a junc- 
tion between a wave guide and a coaxial line 
which would operate over a frequency band- 
width greater than 2:1 with a voltage standing- 
wave ratio of less than 2. Several types of 
junctions satisfying these requirements were de- 
signed, using simple transmission line theory.®®^ 
Some of these employed ridge wave guide of the 
type described previously.^®® The best of the 
simple junctions investigated and analyzed was 
found to have a bandwidth ratio of 2.7:1. 

Studies of Filters 

It has long been known that certain lumped - 
constant four-terminal networks possess useful 


MISCELLANEOUS TLIEORETICAL INVESTIGATIONS 


135 


filter characteristics. As frequencies are in- 
creased, however, lumped constants (first induct- 
ances, then capacitances) become increasingly 
difficult to realize physically. A fairly complete 
investigation was therefore undertaken to extend 
these filter concepts to circuits including sections 
of transmission fines, for use at ultrahigh fre- 
quency. The basic method of analysis and the 
resulting design-equation methods are discussed 
in the accompanying monograph,®®^ and the 
summary given is therefore very brief. 

Filters Using Short Sections. Short sections of 
transmission fine (less than a quarter-wave in 
length) which are terminated in an open circuit 
or a short circuit are electrically very nearly 
equivalent to lumped constants. A short-cir- 
cuited section less than an eighth of a wavelength 
long is particularly useful, and behaves like a 
lumped inductance. Thus, one can design many 
lumped-constant filters so that the coil can be 
replaced by fine sections. Design equations and 
methods were derived for several filters and 
transformers using this method of construction.^-^ 
Types of filters considered included one low-pass, 
one high-pass, and several band-pass filters. 
The theoretical results agreed fairly closely with 
experimental curves. The design equations were 
later extended to an improved low-pass filter of 
similar type.®®® This latter filter was easily con- 
structed and could be built of wave guide as well 
as coaxial fine, to operate in the microwave 
region; it consisted of short lengths of alternately 
high- and low-impedance sections of transmission 
fine connected in series. 

Filters Using Resonant Sections. As frequencies 
of operation are increased, the short-section 
coaxial filters described above become mechani- 
cally inconvenient because of the small size of 
the fine sections, and recourse to filters involving 
resonant sections of fine becomes necessary. A 
general method was developed for analyzing all 
types of coaxial filters, and design equations 
were derived for a number of band-pass and 
low-pass sections filters. Matrix algebra was 
used in the attack on the problem, and the 
results of the analysis were tabulated. ®i^ A simi- 
lar analysis was performed on an easily con- 
structed high-pass filter of this type.®^^ Consider- 
ation was given to the question of spurious 
responses in a low-pass filter, and formulas were 
derived which enable the design of one type to 


be carried out so that some of the spurious pass 
bands cancel and more nearly ideal low-pass 
characteristics are obtained o®^® At a later date 
the design equations mentioned above were 
revised, and the new data summarized in tabular 
form, including the results of some additional 
types of filters. ®^^ 

It was shown that the optimum response of 
series-coupled circuits is independent of the type 
of nonresonant coupling and depends only on 
the number of resonant cavities, the allowed 
mid-band loss, the bandwidth, and the center 
frequencies.®^® Universal curves were drawn for 
such circuits for the case of optimum response. 
The results hold equally well for lumped circuits. 

General Properties of Filters. The problem of 
filter pass-band loss due to mismatch in receiver 
r-f fines was considered. ®^^ A filter operates 
properly only if it is terminated at both ends in 
the impedance for which it was designed. Formu- 
las and curves were derived for the maximum and 
minimum possible mismatch and insertion-loss 
values; the results showed that the standing- 
wave ratios of the receiver input and of the 
antenna should be kept lower than is commonly 
supposed, if filters are to be used. 

A study was made of the universal character- 
istics of triple-resonant band-pass filters.'^®® The 
universal insertion-loss characteristic was calcu- 
lated as a function of frequency for a band-pass 
filter composed of one, two, or three lossless 
resonant circuits in a loosely coupled cascade 
connection between a source and a load im- 
pedance. Consideration was given to the effect 
of load and source coupling upon pass-band 
insertion-loss variation and upon bandwidth. 
The results were summarized in the form of 
universal response curves for filters of this type. 

6 ‘ MISCELLANEOUS THEORETICAL 
INVESTIGATIONS 

In addition to the studies reported in the fore- 
going sections, there were a number of investi- 
gations, mostly rather brief, which cannot be 
included in the major classifications above. 
These included an analysis of the operation of 
magnetrons, studies of the probability theory 
involved in making radar intercepts with search 
receivers, calculations of jamming effectiveness, 
and so forth. 


136 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


^ Magnetron Studies 

Not much theoretical effort was expended on 
magnetrons in Division 15; some work was 
carried through, however, in particular on the 
study of space-charge limited, single-stream 
solutions in a cylindrical magnetron with small 
current (see also Chapter 3). 

The complete first-order solution for the radial 
motion of the electron was found to be 

^ = — = J?JA — I — ^ V cir. 

Tc 


where 

e{t) = 

4>{i) = 

Rod) = 

CCi{t) = 

m = 

0 _ 0' = - 0(0 = j coi (n dt", (109f) 

where aU quantities defined in equation (109), 
with the exception of e(^), depend on as well as 
upon those other quantities which are explicitly 
stated. In equations (108) and (109), r is the 
distance of the electron from the axis, t is time, 
Tc = cathode radius, and w = eH/mc. In this 
latter, e is the electronic charge, m its mass, 
c the velocity of Hght, and H the applied static 
magnetic field. The motion of the electron is 
also subject to a radial electric field E = E{r,t). 
The quantity I{t) is the current per unit length 
through the magnetron, consisting of the sum 
of the electronic and displacement currents, and 
is a function of the time alone, independent of r. 

Brillouin’s theory of the plane magnetron®^^ 
was extended to cylindrical magnetrons, on the 
condition that the current I is small enough 
so that 


X 


2 \ coi(^) / 

Ro{f 






ieljt) 


CO r e{t') dt', 

J to 

[ 0(0 + V 1 + <t>dy 1 

iO )’ 

r (o dt', 

J to 


(109a) 

(109b) 

(109c) 

(109d) 

(109e) 


nt 


e(t) = 


ieljl) 
mr^ co^ 


<< I. 


( 110 ) 


This restriction is generally well satisfied under 


normal conditions and does not require the cur- 
rent to be unreasonably small. 

Results of Analysis 

The analytical method developed®^^ allows an 
expansion in increasing powers of e and was 
exphcitly carried out to include the linear terms, 
giving in this approximation the distance of an 
electron from the cathode as a function of time 
in terms of simple integrals and with the current 
I an arbitrary function of time. As in the above- 
mentioned theory, it was assumed that the solu- 
tions are of the single-stream type where all 
electrons which at a certain time are found at a 
given position have the same velocity. It was 
then investigated under what conditions this 
original assumption is justified, and it was found 
that the conditions for a single-stream solution 
are not nearly so general as they seem to appear 
from the plane case. 

In the first place, it was found that an original 
single-stream solution can break down sooner or 
later, depending entirely on the time dependence 
of the current. In the second instance, any 
single-stream solution established while a positive 
current was flowing breaks down a sufficient 
time after cessation of the current. This indi- 
cates the possibility of transitory multiple-stream 
states, at least in certain cases, and, without 
adequate methods for their investigation, pre- 
cludes any safe conclusions concerning the ulti- 
mate stationary state which must be reached if 
the anode voltage, after having increased from 
zero to a certain value, is held fixed. 


^ ^ Search Receiver Probabilities 

In connection with the problem of the best 
design and method of operation for radar search 
receivers, the question arose of the probability 
that a receiver sweeping in frequency would in- 
tercept a radar with a rotating antenna — ^in 
other words, the probability that the receiver 
frequency would coincide with that of the radar 
(within the receiver bandwidth) at the same 
time that the radar antenna was pointing toward 
the receiver. The problem was complicated by 
the fact that the antenna of the search receiver 
was sometimes directional and rotating. A 
number of studies were attempted. The rigorous 


MISCELLANEOUS THEORETICAL INVESTIGATIONS 


137 


solution of the problem proved quite elusive, 
although some special cases of interest were 
treated successfully. 

Rigorous Analysis 

Some work was also done on the problem of 
simultaneous periodically recurring events, in 
which formulas were derived for the probability 
that two events, each recurring with a definite 
period and lasting for a definite length of time, 
occur simultaneously at least once in some given 
time interval. The further condition may be 
added that the simultaneous occurrence itself 
must have at least a given minimum duration. 

Approximate Solutions 

An adequate engineering approximation to the 
intercept problem, while not rigorous, was also 
constructed, characterized by comparatively 
simple formulas and theory. It was felt that the 
results were adequate to predict the performance 
to be expected with sufficient accuracy, and this 
behef was confirmed by experiment. 

Theoretical Analysis. The one important thing 
from an operational standpoint is what we may 
call a “characteristic” time U which determines 
the time scale against which a more or less uni- 
versal probabihty curve can be plotted. In other 
words, the probabihty P of interception by time 
t may, for rough practical purposes, be taken 
of the form 



where / is a universal function. The important 
quantity is obviously the constant U which 
governs the time scale. The formula for is 


periods. There is no doubt but that for small 
values of P or t/ta, the function fit/U) is merely 
t/tQ, since then questions of redundant proba- 
bilities, overlaps, etc., do not enter. When P gets 
somewhat larger, say, in the vicinity of 50 per 
cent, there are more complications involved in 
the determination of the theoretical probabihty. 

A distinction can be made between three 
cases, which can be characterized respectively as 
the monochromatic, uncorrelated, and “ignora- 
mus” cases, as follows. 

1. In the monochromatic case it is supposed 
that the enemy radar has a perfectly definite 
frequency. The theoretical curve of probabihty 
of finding the enemy within a time t is then a 
series of straight hnes, each segment with lower 
slope than the preceding. The reduction in slope 
after a certain time is due to the phenomenon of 
overlap. In case the problem is only one of two 
coincident events (omnidirectional antenna or 
100-per cent acceptance bands), it has been 
shown that there should be only two segments 
of appreciable length. The points at which the 
breaks occur are conditioned by the relations of 
commensurability between the various periods, 
and this is what makes the phenomenon poten- 
tially so comphcated. If the enemy frequency 
happens to have just the right value, the slope 
of the curve can be horizontal after a certain 
value of the time, so that the maximum achiev- 
able probability is less than 100 per cent (under 
50 per cent in certain cases). Of course the 
probability is zero that the enemy frequency 
will have one of these particular values, but 
there are certain small ranges of frequencies such 
that we cannot be sure of intercepting the enemy 


^0 = 


TnTsTA 


[sQoj I ^ 


+ 




IA%\t 


+ 


(BA. 

\360/ ""VSOO/^ 


( 111 ) 


where Ta, Ts are respectively the periods, in 
seconds, of the enemy radar, of our antenna, and 
of our sweep. Also Br and Ba are respectively 
the beamwidths, in degrees, of the enemy 
antennas and our antennas, while A% is the 
acceptance percentage of our receiver. It is 
assumed that our apparatus has been designed 
with reasonable intelligence, so that particular 
antenna directions are not excluded because of 
correlation between the sweep and antenna 


in, say, 1,000 years. Obviously, the chance of the 
frequency being in such a critical zone is negli- 
gibly small, and what is needed is a theory that 
allows in a reasonable way for uncertainty in 
the enemy frequency. 

2. A procedure which attempts to allow for 
the uncertainty is provided by the uncorrelated 
model. Here it is assumed that the probability 
of finding an event in a time interval ^ to (^ -f dt) 
is independent of t, except for a “cutout” factor 


138 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


(1 — P) which allows for the fact that we do not 
count an interception as new if one has already 
been made. The appropriate differential equa- 
tion is thus 

of which the solution is 

p = 1 _ (112) 

with to as in equation (111). The quite valid 
objection was raised against this formula that 


results over different values of the enemy fre- 
quency so as to have aU commensurability and 
incommensurability situations. This was at- 
tempted, with the help of previous results and 
with certain none-too-good approximations made 
in connection with the averaging. Also it must 
be assumed that the enemy beamwidth is not 
too large, and that the time our antenna is “on 
target” is small compared to that during which 
the enemy is sweeping through us. The calcula- 



Figure 38. Radar intercept. Probability of success in time t as a function of Tan. Comparison of 
uncorrelated and ignoramus theories. 


the ideas on which it is based are too naive. 
Specifically, no cognizance is taken of the fact 
that the overlapping or commensurability phe- 
nomena may make the probabilities dependent 
on time. 

3. Obviously, what is needed is what may be 
characterized as an ignoramus theory. Here it 
is assumed the ignorance of the enemy frequency 
is great enough to embrace all possible cases of 
tuning and detuning with respect to commen- 
surability relations. We then make a calculation 
with the monochromatic theory, but average the 


tion gives the following formula for the proba- 
bility 



P=-|(r-l)Mog(^)+| + f, (r^l), 

(113) 

where r = t/to, with U as in equation (111). 

The results of equations (113) and (112) (the 
ignoramus and uncorrelated theories) are com- 
pared in Figure 38. It is seen that the differences 
between the two theories are inconsequential 


MISCELLANEOUS THEORETICAL INVESTIGATIONS 


139 


compared to other operational difficulties and 
uncertainties. As would be expected, the 
ignoramus theory gives lower probabilities for 
large values of the time, but somewhat higher 
probabilities in the intermediate zone, as the 
commensurable cases tend to inhibit interception 
for certain kinds of tuning, but do not become 
operative until a certain time has elapsed. It is 
not surprising that the two theories should agree 



INTERCEPT TIKE IK MINUTES 


Figure 39. Intercept probability effect of di- 
rection-finding antenna ; comparison of the 
various theories with experimental results. 


quite well from a quahtative standpoint, as 
averaging over the various possible values of 
the enemy period tends to smooth over the 
various correlation effects due to much or httle 
commensur ability. Still it is to be emphasized 
that the two theories are not identical, as 
averaging over different amounts of commensura- 
bihty is not equivalent to omitting correlation 
entirely. 

Comparison with Experimental Results. On the 
whole, either equation (112) or (113) reproduces 
quite well the results obtained experimentally 


by motor-driven devices for recording coinci- 
dences.^®® Figure 39 is a typical case, although 
the agreement is not quite so good for some of 
the other examples. The uncorrelated and 
ignoramus forms of theory are indicated respec- 
tively by dashed and solid lines. For low values 
of the probabihty, the theory and experiment 
should agree exactly, as in this zone sufficient 
time has not elapsed for questions of correlation 
to enter, and all forms of theory are the same. 
It is not clear why the experimental curves, while 
agreeing quite well with the uncorrelated and 
ignoramus theories, do not agree at all with what 
one would obtain with a monochromatic theory. 
Ideally, one knows all the periods involved, so 
that the experimental model should behave in a 
monochromatic fashion. If the experimental 
data were taken completely at face value in, for 
example, the omnidirectional case of Figure 39, 
the periods are exactly in the ratio 6:1, and after 
six sweeps nothing new would be found, so that 
the saturation value of the probability would be 
in the neighborhood of 10 per cent. To explain 
the fact that actually no such saturation is found, 
it is necessary to suppose that the recorded 
periods are only accurate to 2 per cent or so. In 
some of the other examples the deviations in 
frequency required to destroy commensurabihty 
are even smaller. If the frequency fluctuated 
from one sweep to another, one might expect 
the uncorrelated theory to apply, whereas if it 
varied only from one run to another, the igno- 
ramus form would be the more suitable. One 
would conjecture that the former situation was 
more hkely to arise experimentally, but the latter 
model seems to agree somewhat better with the 
experimental results. The fact that small devia- 
tions in frequency obliterate the commensu- 
rability relations makes one suspect that even if 
one knew the enemy frequency, the monochro- 
matic assumption would not apply as weU as the 
other, more statistical forms of the theory. 


Operational and Miscellaneous Studies 

A number of problems received only very brief 
theoretical treatment, although some of them 
were of considerable operational significance. 
Included among these were several calculations 
of the jamming effectiveness of proposed counter- 


140 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


measures, as well as some miscellaneous in- 
vestigations. 

Jamming Effectiveness Calculations 

Theoretical calculations were made on the 
jamming effectiveness of various proposed RCM 
devices, methods, and techniques, in some cases 
to check on minimum jamming distances or 
similar points, in other cases to decide whether 
the proposed countermeasure was worth using 
at all. 

Radar Chicks."^ One such study was con- 
cerned with an estimate of the practicability of 
using expendable jammers (Chicks) for radar 
countermeasures purposes. Three types of 
Chicks were considered: parachute-borne jam- 
mers to screen during the period of fall, floating 
jammers for the screening of small boats and 
barges, and grounded jammers to be dropped 
from planes into enemy territory. The effects 
of floating Chicks were compared to those of 
corner reflectors (see Section 6.3). The results, 
based on the available data as of September 
1943, indicated that: 

1. Parachute Chicks appear to be of practical 
use against ground-controUed interception [GCI] 
or gun laying [GL] in raids against isolated 
targets whose location and frequency are ac- 
curately known; in other cases too large a volume 
and weight are required. 

2. Parachute Chicks are not useful for screen- 
ing boats, except possibly those of higher speed. 

3. Parachute Chicks are not effective against 
aircraft interception [AI]. 

4. Parachute Chicks could be used against 
early-warning [EW] radar. 

Floats carrying either corner reflectors or 
Chicks could be useful in screening barges and 
small boats, whereas grounded Chicks appear to 
have only a nuisance value and are generally 
impractical for RCM purposes. 

Effectiveness of GCI Jammers. In the summer 
of 1943, calculations were made®°^ to determine 
the effective ranges of two high-power ground 
transmitters designed to jam the German GCI 
system. One of these was on 40 me (Cigar) for 
use against the ground-to-fighter communica- 
tions, the other (Tuba) on 500 me to jam the AI 
radar. It was concluded (to smnmarize the 
results in a very general way) that these trans- 
"'See Chapter 8 for discussion of communications Chicks. 


mitters would be effective at ranges up to 200 
miles, under optimum conditions, if sufficiently 
high antenna gains were used. 

Jamming of Radio Altimeters. A study^^° con- 
cerned with jamming the German FGlOl, 
FGIOIA, and FG103 radio altimeters was under- 
taken in the early months of 1944. On the basis 
of the best information available at the time, an 
attempt was accordingly made to determine the 
necessary jamming power in various tactical 
situations. It was found that in all cases the 
power required was so great as to demand large 
installations and antennas of large gain. Doubt 
was expressed as to the value of jamming 
piloted planes if such installations were made 
available. 

Miscellaneous Studies 

An analysis was made to determine the proper 
method of interpreting operational data on the 
effectiveness of countermeasures in actual use. 
In addition, an investigation was made of the 
possibihty of designing a steel cable with very 
low radar reflectivity. 

Operational Analysis Methods. Among the 
otherwise unclassified studies was an analysis of 
the effectiveness of countermeasures. The 
study indicated that to judge the effectiveness 
of a countermeasure one must compare the data 
actually obtained with those which one would 
expect if the countermeasure were ineffective. 
The results in the latter case are of essentially 
statistical character. Procedures are described 
for obtaining a quantitative estimate of effec- 
tiveness, and for judging the significance of the 
result. 

Low-Reflectivity Cable. A miscellaneous prob- 
lem of some interest was the design of an armored 
steel cable with low radar reflectivity,^^^ for use 
in the target practice of radar-controUed anti- 
aircraft guns. On such practice, an expendable 
flying radar target is needed. A target of this 
kind can be obtained by towing a nylon sleeve 
behind an airplane and either attaching, close to 
the sleeve, a small corner reflector or weaving a 
great number of half-wave dipoles into the sleeve. 
It can easily be made to have a cross section 
equal to that of an airplane and would be per- 
fectly adequate except for disturbing radar 
returns, originating from the cable by which the 
target is towed behind the plane. Accordingly, 


MISCELLANEOUS DEVELOPMENTS AND RESEARCH STUDIES 


141 


a special cable was developed. It works on the 
principle of a transmission Line with periodically 
varying self-induction and has the property that 
its (radar) cross section is about five times 
smaller than that of a continuous steel cable of 
the same dimensions. The theory and design 
of the cable were worked out, and laboratory 
tests were made on manufactured samples.^^^ 

MISCELLANEOUS DEVELOPMENTS 
AND RESEARCH STUDIES 

It was found necessary to carry on a variety 
of unrelated miscellaneous developments and re- 
search studies in support of the RCM program 
of Division 15. These were mainly experimental 
in nature. The more important ones are described 
briefiy below. 

Use of Models in Antenna 
Investigations 

It is theoretically possible to construct a model 
of an electromagnetic system which is an exact 
simulation of the prototype. The simulation 
will be exact if the dimensions of the model are 
made 1/w, if the dielectric constants are un- 
changed, and if the frequency and conductivities 
are n times those of the prototype, where n is 
an arbitrary scahng factor. 

Methods for measuring the patterns of an- 
tennas by means of models have been investigated 
to obtain information needed in designing an- 
tennas having specified patterns. Most emphasis 
in the investigations has been placed on aircraft 
antennas. 

Methods for Measuring the Patterns of 
Model Antennas 

The methods used for measuring the patterns 
of full-scale antennas are in general apphcable to 
measurements on a model. However, the acces- 
sibihty and convenience of handling a model 
result in differences in the equipment and tech- 
nique employed. The methods which have been 
investigated on models may be broadly classified 
as follows. 

Method I: Direct Measurement of the Pattern 
as a Transmitting Antenna. In this method a 


transmitter is used to excite the model antennas. 
A receiver with an antenna arranged to measure 
the desired component may then be used to 
explore the field radiated by the model. 

Method II: Direct Measurement of the Pattern 
as a Receiving Antenna. This method is similar 
to the above, except that the transmitter is used 
to explore the sensitivity of the model antenna 
as a function of direction. By virtue of the 
reciprocity theorem, the pattern so obtained is 
similar in shape to the corresponding pattern 
measured when the model antenna is trans 
mitting. 

Method III: Measurement of the Reradiation 
from a Receiving Antenna. This method is essen- 
tially a combination of the previous two methods. 
A remotely located transmitting antenna is 
excited by an unmodulated transmitter sending 
a wave toward the model. This wave induces 
currents in the model antenna which are a func- 
tion of the impedance connected to its terminals. 
If the termination impedance is made to vary 
periodically, the field reradiated from the model 
antenna will also vary periodically. The re- 
sultant modulation permits the reradiated field 
to be distinguished from the primary or exciting 
field. In practice, the reradiated field which 
returns along the transmitted ray (i. e., the echo) 
is measured. The pattern obtained in this way 
is the product of the pattern for reception by the 
pattern for transmission. Since these are similar, 
the measured pattern is the square of the an- 
tenna pattern. 

Airborne Antennas 

One of the principal problems to be solved in 
designing equipment for making pattern measure- 
ments on antenna models is that of controlling 
stray refiections. Avoidance of distortion of the 
pattern by reflections from the ground is par- 
ticularly important. The obvious procedure is 
to elevate the equipment and use sufficient 
directivity at the measuring antenna to minimize 
the pickup of ground reflections. Another 
method uses the earth as part of the directive 
antenna at the observing position. 

Most of the investigations of models of air- 
borne antennas have been made in the frequency 
range 500 to 10,000 me. In this region it is 
possible to control ground reflections with a 
highly directive antenna at the observing position 


142 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


while keeping the equipment at a reasonable 
height (8 to 10 ft) above the ground. The direc- 
tive antenna usually consists of a pyramidal horn 
of rectangular cross section, designed to have 
equal directivity in its two principal planes. 
Such an antenna is easy to feed over a wide 
frequency range and has linear polarization and 
adequate directivity. At frequencies less than 
approximately 500 me, it becomes difficult to 
control ground reflections with equipment of 
reasonable size. 

The model is mounted on a tower located at a 
distance from the horn aperture which is suf- 
ficient to insure that the field is essentially 
uniform over the region occupied by the model. 
The minimum distance which can be used 
depends on the size of the model and other 
factors. The tower which supports the model 
must be carefully designed to minimize dis- 
tortion of the field. 

For frequencies less than about 2,500 me, the 
physical size of oscillators which are presently 
available make it impractical to mount the oscil- 
lator in the usual sizes of models. Above 2,500 
me, certain types of oscillators (klystrons and 
other veolcity-modulated oscillators) are com- 
pact enough to mount in the model, provided 
leads can be used to conduct power supplies 
located at the observing position. These leads 
have to carry voltages which may run as high 
as 2,000, so that it is preferable to use other 
measuring techniques, if possible. However, this 
technique seems to be the only practical one for 
K-band frequencies. 

Method II has been found to be the most 
useful method for the frequency range 500 to 
10,000 me. The transmitter used to excite the 
horn located at the observing position may be 
any convenient oscillator of suitable frequency 
and power capability. If the transmitter is tone- 
modulated, a very simple receiver consisting of 
a tuned crystal or bolometer detector may be 
used in the model. The audio output of the 
detector is conducted to the observing position 
by wires which are so located in the field as to 
produce minimum distortion of the model an- 
tenna pattern. 

Method III has a number of disadvantages 
which limit its usefulness. The principal limita- 
tion is lack of a suitable modulator for use in the 
model. The only type which was tested con- 


sisted of a special vibrator with contacts to 
open and close the antenna circuit. The vibrator 
was not sufficiently stable mechanically and 
produced very little modulation at frequencies 
above 2,000 me. An alternative modulator using 
nonhnear impedances (crystals, for example) 
which are made to vary periodically by suitable 
biasing arrangement, has been considered but not 
tested. The principal disadvantage of the 
method, however, is the need for a phasing adjust- 
ment before each reading is taken. This makes 
automatic recording of the pattern impractical. 
Further, any lead wires to the model wiU distort 
the pattern even though they are shielded. 

For frequencies below 500 me, ground reflec- 
tions can be best controlled by arranging the 
equipment to operate vertically instead of hori- 
zontally. The ground then becomes part of the 
antenna system at the observing position. 
Method I is probably the most useful one in this 
frequency range. Battery-operated transmitters 
of small physical size can be readily constructed 
for installation in the model. A standard super- 
heterodyne receiver with a short dipole or verti- 
cal-loop antenna can be used on the ground 
directly beneath the model. The reflection of 
the transmitted wave at the ground will produce 
standing waves which may distort the pattern. 
If the model is small in terms of wavelength, 
it may be located at a maximum in the standing 
wave. Alternatively, a high impedance inserted 
in series with the antenna lead in the model will 
minimize the distortion by reducing the variation 
in circuit impedance due to the reflected wave. 

At low frequencies. Method II is probably not 
too useful since the model will, in general, be 
too small in terms of the wavelength to shield 
properly the lead wires from the model to the 
observing position. Method III has not been 
tested at these low frequencies but should be 
useful. It is probable that the phasing adjust- 
ment need not be made with each reading when 
the model is small in terms of the wavelength. 

The use of some form of automatic recorder at 
the observing position has been found to be 
highly desirable. An Esterhne- Angus strip-chart 
recorder is very convenient and rapid, but gives 
a presentation which is not so readily interpreted 
as a polar presentation. A hand-operated 
mechanical transcriber has been constructed for 
converting the strip-chart record to polar form. 


MISCELLANEOUS DEVELOPMENTS AND RESEARCH STUDIES 


143 


A specially constructed polar recorder has been 
obtained from Leeds and Northrup and found 
to be very satisfactory. Recorders can be syn- 
chronized with the rotation of the model by 
selsyns or equivalent devices. The bolometer 
and crystal detectors used as receivers are ap- 
proximately square law so that the range of 
signal to be recorded is rather large. A special 
amphtier^® with a square-root characteristic has 
been designed to provide compression for re- 
cording. 

In modeling an antenna for pattern measure- 
ments, ordinarily it is not necessary to have an 
exact simulation of the physical details. Details 
of the prototype which are small in terms of the 
wavelength are usually not important. Many 
types of antennas have been m^easured with 
models.^®’^^’ It has also been found feasi- 

ble to model simple antenna arrays^- and 
systems. 

Models have been used for measuring propeller 
modulation. A method for measming the 
eUipticity of the polarization radiated from an 
antenna, including the direction of rotation of 
the electric vector around the ellipse, has also 
been developed. Development of methods for 
investigating direction-finder antennas has also 
shown considerable promise. 

Shipboard Antennas 

Methods and techniques^® for measuring the 
patterns of ship-borne antennas by means of 
models were investigated. The problem is not 
essentially different from the aircraft problem 
except for the effect of the sea. 

For frequencies below about 100 me the sea 
acts hke a perfect reflector for all practical 
purposes. Hence it can be simulated by con- 
structing an image of the ship and feeding the 
antenna and its image with currents of the proper 
phase and magnitude. Alternatively, the sea 
may be simulated by a large metallic area, with 
the ship model located near its center. It is 
essential to terminate the edges of the metallic 
area in such a way as to reduce the reflection 
from the edge discontinuity. One method^® is to 
serrate the edges and place poorly conducting 
material between the serrations. An improved 
method^^ employing special absorbing screens 
was also developed. 


Ground-Based Antennas 

The simulation of the effect of a finitely con- 
ducting earth is perhaps the most difficult prob- 
lem in modeling antennas. Theoretically, the 
earth could be simulated by using a material of 
conductivity n times that of the earth and a 
dielectric constant which is unchanged. Actu- 
ally, such a material is not readily obtained. 
Even if such a material were available, a thick- 
ness of quite a few feet would be needed in order 
that the wave reflected from the underside of 
the section would be sufficiently absorbed. 

It is sometimes possible to avoid the problem 
of simulating the ground. For example, if the 
frequency of the prototype is low enough, it may 
be possible to assume that the earth is a perfect 
conductor, in which case simulation may be 
obtained as with the sea. On the other hand, 
if the frequency is high enough and the structure 
on which the antenna is located is large enough, 
it may be possible to measure the pattern with 
the model of the antenna and mounting structure 
in “free space. The effect of the earth on the 
pattern may then be estimated from theoretical 
considerations.^® 

Model Methods for Measuring Antenna 
Impedances 

An investigational was carried out to determine 
the feasibility of measming the impedances of 
antennas by means of models. For an accurate 
simulation of the antenna impedance, it is neces- 
sary to make the model with great care. The 
principal difficulty is in modeling the base of the 
antenna, with its associated connectors, etc., 
which has a much larger effect on the impedance 
than on the pattern. 


Use of Models in Studying 
Radar Echoes 

For investigations of echoes from targets it is 
not always feasible to use actual radar equip- 
ment with full-scale targets. The lack of control 
over the target orientation is particularly bother- 
some in measurements on aircraft in flight. For 
these and other reasons, it was found desirable 
to investigate the possibilities of using models. 

The usual pulse technique used in radar equip- 


144 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


ment is not suited to model measurements be- 
cause of the difficulty in obtaining pulses of 
sufficiently short duration to permit working at 
close range. For this reason, other methods for 
measuring the echo were tried. Separate trans- 
mitting and receiving equipment can be used, 
with the antennas placed as close together as 
possible. Such an arrangement is useful for some 
measurements, but suffers from the disadvan- 
tage that the path of the echo ray does not 
coincide with the path of the transmitted ray, 
as in actual radeir operation. A method for 
avoiding this has been developed in which the 
transmitter and receiver use a common radiating 
system. A horn is used with the transmitter 
excitation connected in the usual manner. The 
receiver is connected to an antenna array which 
is located inside the common wave guide. The 
array used for most of the measurements has 
consisted of one cyhndrical stub connected to the 
receiver, and two parasitic stubs spaced about 
3^ wavelength each side of the main element 
and located on the center line of the wave guide. 
It was found to be possible to adjust the lengths 
of the parasitic elements to give practically 
complete suppression of the outgoing wave at 
the receiver terminals, while retaining sensi- 
tivity to incoming signals. 

Several methods for calibrating the equipment 
have been developed. A number of spheres were 
tested to determine the relative variation of 
echo area with radius. It was found that the 
curve of variation had the same relative shape 
as predicted theoretically. It seems to be a safe 
assumption, therefore, that the computed echo 
area will be correct. A second method of cah- 
bration was tried in which circular and square 
plates were used. The echo area computed on 
the basis of geometrical optics was assumed to 
be correct for plates whose edges are long in 
terms of the wavelength. 

Measurements^^ have been made of the echo 
patterns of large bombers at 200 me. Methods 
for investigating the propeller modulation of 
radar echoes have been investigated. The pat- 
terns^®’^^’ of several sizes of corner reflectors 
have been measured. Measurements^'^ of the 
echoes from tow cables have also been made. 

6-5.3 Magnetron Filament Regulator 

Back heating in magnetrons tends to overheat 


the magnetron cathode and may shorten its life 
considerably. The deleterious effects of back 
heating can be minimized if the power applied 
to heat the cathode is decreased by an amount 
equal to the power supplied by back heating. A 
circuit has been devised to provide this compen- 
sation electromechanically, in which the primary 
of the filament transformer is one arm of a self- 
balancing impedance bridge. Use of a step-up 
transformer in the comparison arm of the bridge 
permits the application of about 90 per cent of 
the line voltage across the filament transformer 
without loss of bridge sensitivity. Immediate 
conversion to direct current of the a-c signals 
across the arms of the bridge makes the circuit 
frequency -independent. The bridge difference- 
voltage is amplified in a pentode whose output 
actuates a differential relay. This relay in turn 
operates a reversing motor which adjusts the 
Variac supplying the primary voltage to the 
bridge. The motor runs until the filament re- 
sistance reflected through the filament trans- 
former is restored to within 3 per cent of the 
value for which the system has been preset. 

Several of these regulators have been built and 
are in use in magnetron test sets and life-test 
racks. 

Regrdators of this type can be used as line- 
voltage regulators for loads of any magnitude if 
the primary of the filament transformer is re- 
placed by a dummy load whose resistance is a 
function of current (e. g., a lamp bulb). 

Some difficulty was experienced with the mag- 
netron filament regulator because of hunting. 
This difficulty was eliminated and critically 
damped operation achieved by the inclusion of 
a tachometer feedback circuit associated with 
the motor which drives the Variac. 


^ Study of Electron Paths in 

Magnetrons and Triodes 

The General Electric differential analyzer can 
integrate the equations of motion of an electron 
in crossed electric and magnetic fields and can 
plot out the electron path in two dimensions 
automatically. Simultaneous plots can be 
obtained of electron velocity components as 
functions of time and of currents induced in 
electrodes. Alternating electric fields can be 


MISCELLANEOUS DEVELOPMENTS AND RESEARCH STUDIES 


145 


included and transit time effects analyzed. The 
one limitation of this procedure hes in the fact 
that space-charge effects cannot be included. 
However, many of the operating characteristics 
of h-f tubes can be deduced more or less quan- 
titatively, even if space-charge effects are 
neglected. 

Electron paths in spht-anode magnetrons have 
been run under a variety of conditions. The 
analyzer shows in a very striking fashion that 
electrons tend to synchronize with the forward 
rotating component of the electric field over a 
wide range of frequencies. They do this by 
spirahng in small loops and “waiting” for the 
field to catch up with them. Several secondary 
electron paths starting on the anode face have 
been traced and the suspicion that secondary 
emission may act as a serious load on a magne- 
tron has been supported. Further work which 
it is hoped can be run on the analyzer includes 
the tracing of paths of electrons which escape 
through the anode shields and a study of the 
a-c level necessary for synchronization of elec- 
trons. It is hoped that the latter study may 
throw some hght on the troublesome failure of 
magnetrons to oscillate at low power levels. 

The problem of electron paths in parallel-plane 
triodes is, of course, even simpler for the analyzer 
than the magnetron problem, although it is still 
too complex for analytical treatment. The 
parallel-plane triode geometry has been set up 
and a number of electron paths have been traced. 
Three important conclusions have emerged from 
a study of these paths. First, it has been shown 
that attention to the impedance levels of the 
external circuits should yield much higher 
operating efficiencies than have been obtained 
experimentally. Second, it is now clear that 
rather high peak emission is required periodically 
from the cathode. It is possible that the cathodes 
which have been used have not been capable of 
emitting these high cmrents. Third, the grid- 
anode transit time has proved to be more 
important than was expected. It would appear 
that inclusion of a screen grid might result in 
materially increased efficiency. Other minor 
unknowns have also been removed — the area of 
the cathode which is inactive because it lies in 
the shadow of the grid wires has been delineated, 
and the cathode back-heating phenomenon which 
appears at high frequencies is now attributable 


to electrons returning at a particular phase of 
the a-c wave. 

It seems evident that the differential analyzer 
will prove to be a very powerful tool in the 
design of future microwave tubes, since it pro- 
vides a fast and accurate method for solving 
problems which would be hopeless analytically. 
Moreover, a complete energy balance can be set 
up and energy losses can be tracked down to the 
basic components and phenomena with which 
they are associated. Information of this type 
can rarely be obtained experimentally. 

^ Gold-Copper Alloy Solder 

In assembling metal vacuum tubes with copper 
parts, most of the solder joints are usually made 
with silver-copper eutectic solder, melting at 
778 C. Frequently, it would be desirable to do 
the soldering in several steps if only a solder were 
available whose melting point lay between 778 C 
and the melting point of copper, 1,082 C. 

Alloys are to be avoided which are low in 
copper and dissolve copper out of the tube parts 
to form eutectics, or which have long plastic 
ranges or brittle phases. These considerations 
exclude other silver-copper alloys than the eutec- 
tic but suggest the use of gold-copper alloys 
having more than 60 per cent copper (by weight) . 

The combination 62.5 per cent copper, 37.5 
per cent gold has been chosen as being safely 
clear of brittle phases and having a useful melting 
range (950 to 980 C) . Soldered joints^^® made 
with this alloy at a furnace temperature of 
1,040 C are vacuum-tight and mechanically 
strong. 

This alloy is equally satisfactory for soldering 
Fernico to copper. Unhke silver solders, it does 
not penetrate appreciably into the grain bound- 
aries of the Fernico. 

In wire form this alloy can be used in making 
copper-to-copper diffusion seals. The seal formed 
by baking under pressure for 2 hr at 450 C is 
vacuum-tight and seems to be stronger mechani- 
cally than pure gold diffusion seals. 

^ ® * Analysis of Behavior of 

Homing Missiles 

An analytical study^^^ was made of the be- 
havior of missiles designed to home on radar 


146 


THEORETICAL STUDIES AND MISCELLANEOUS DEVELOPMENTS 


stations by translating information received at 
an antenna array (two Adcock antennas and a 
pair of crossed dipoles) into motion of control 
surfaces (rudder and ailerons). The behavior of 
the missile was assumed to be such that the 
controls follow instantaneously the instructions 
received from the antenna array. An investiga- 
tion was made of the effects on the missile of 
field distributions from ground reflections or 
other spurious radiating sources. The results 
are apphcable to homing systems and radio 
direction-finders in general. 

Meteorological Observations for 
Propagation Studies 

From December 20, 1944, to February 27, 
1945, and again from August 1 to September 
30, 1945, meteorological observations were made 
near Hadley Airport, New Jersey, to obtain data 


for correlation with propagation in the 2X and 
X bands. This work was initiated at the request 
of the NDRC Committee on Propagation. The 
transmitters were located on the top of a tower 
at Mount Neshanic, New Jersey. The meteoro- 
logical observations were made at a point near 
the center of the propagation path. 

The primary data consist of low-level sound- 
ings (up to 500 ft) made at 0200, 0600, 1000, 
1400, 1800, and 2200 Eastern War Time. Tem- 
perature and humidity elements were carried 
aloft by a tethered balloon or by a kite. A light 
three-conductor cable connected the elements to 
meters on the ground. The sounding data were 
supplemented by continuous records of tempera- 
ture and wind direction. A mobile Army 
weather station also made possible continuous 
records of wind velocity and barometric pressure. 

The data were turned over to the NDRC 
Committee on Propagation for study and cor- 
relation. 


PART III 


NONRADAR APPLICATIONS 







Chapter 7 


NONRADAR RECEIVING AND DIRECTION-FINDING TECHNIQUES 

AND EQUIPMENT 


INTRODUCTION 

S EVERAL SPECIAL projects covering receiving 
* and direction-finding [DF] techniques were 
undertaken as part of the general nonradar 
countermeasures program carried on by Divi- 
sion 15 laboratories. The receiver projects were 
in many cases a necessary part of the develop- 
ment of jamming equipment. They included not 
only the development of special receivers for 
use in monitoring enemy signals that were to be 
jammed, but also studies of receiver vulnera- 
bility. Most of the projects dealing directly with 
receiver vulnerability are to be found in 
Chapter 9; however, some of them have of 
necessity been included in this section. Special 
studies were made of DF schemes; some of 
this work is discussed in Chapter 4 of this 
report and some of it is discussed in this 
section. 

The work on receiving and DF techniques 
was carried out at Bell Telephone Laboratories, 
Inc. (under contracts OEMsr-778 and 966), 
at the Panoramic Radio Corporation (under 
contract OEMsr-1138), at the Federal Tele- 
communications Laboratories, Inc. (under 
contract OEMsr-1458), at the Radio Corpora- 
tion of America Laboratories (under contract 
OEMsr-895), and at the Airborne Instruments 
Laboratory (under contract OEMsr-1305). 

72 TECHNIQUES 

Division 15 work in this field included the 
development of general techniques and specific 
equipments; this section discusses techniques, 
and the following section, specific equipments. 

Communications Ferrets for Search- 
ing and Monitoring 

General Requirements 

In order to apply countermeasures to the 
enemy’s radio communications circuits effec- 


tively, it is necessary to obtain certain informa- 
tion regarding his facilities and type of traffic. 
Among the technical items on which informa- 
tion is desired are the frequencies in use, the 
type of polarization, type of modulation, direc- 
tion, etc. These data are needed in order to 
determine the type of jamming which will be 
most effective. It is also important to know the 
principal uses of a given circuit, i.e., whether 
the circuit is for tactical purposes, administra- 
tive use, or some other purpose. The use will de- 
termine whether it is more desirable to jam or 
to intercept under a given set of circumstances. 

Such information can be acquired by the use 
of suitable search apparatus. Search receivers 
can be used to intercept and monitor enemy 
transmissions, and DF apparatus can be used 
for determining the direction from which the 
signals arrive. The search apparatus should 
incorporate automatic-recording features to 
indicate the presence of signals and arrange- 
ments for making recordings of enemy trans- 
missions for later interpretation. 

The search receivers, in addition to meeting 
the sensitivity and selectivity requirements of 
good communication receivers, should also meet 
additional requirements peculiar to search 
applications. The receiver requirements for 
airborne and ground installations may differ 
in some respects. 

In either ground or airborne installations, 
however, the chances are that several receivers 
must be used to cover the wide band of fre- 
quencies to be searched for enemy transmis- 
sions. These sets will be in close physical 
proximity, can use common power supplies, and 
will be connected either to a common antenna 
or to closely spaced individual antennas. Under 
these circumstances it is important that they 
should not interfere with each other’s operation 
by emitting excessive radiation from the 
heterodyning oscillators or beat-frequency 
oscillators (fundamental and harmonics) ; 
similarly, interference from such sources by 


149 


150 


NONRADAK RECEIVING AND DIRECTION-FINDING TECHNIQUES 


way of common power supplies must be mini- 
mized. 

If enemy signals of widely different intensi- 
ties are to be searched for, it is important that 
spurious responses in the receivers be suffi- 
ciently suppressed. The most common response 
of this type is the image response, but there 
are many others in present type receivers. 
Unless these responses are well suppressed, a 
transmission arriving with a high carrier in- 
tensity may be picked up at apparently lower 
intensities at several other points on the 
receiver and erroneously recorded as additional 
enemy transmissions at several frequencies. 
Another source of false signals may be caused 
by the generation of harmonics and heterodyne 
products as the result of nonlinear mixer 
characteristics when strong signals are im- 
pressed on the receiver. There is more possi- 
bility of this sort of trouble when the receiver 
input is untuned (as when a buffer r-f stage is 
used to reduce oscillator radiation) than when 
it is tuned. Ordinarily this trouble will not 
occur unless the receiver is located close to a 
powerful transmitter. 

Search receivers should incorporate good noise 
suppressors, such as the Lamb type. The dials 
should be accurately calibrated for direct 
frequency readings, or means for frequency 
calibration should be provided. Receivers for 
ground use should be conservatively designed 
to operate continuously without overheating, 
and those for airborne use should be designed 
to meet severe mechanical stress requirements 
and to operate satisfactorily under extremes of 
temperature variation. It is desirable that 
S-meter readings, or their equivalent, be 
reasonably related to the input signal intensity 
and that provision be made for a panorama- 
scope attachment for aid in determining the 
type of modulation of the enemy transmission 
and for guarding a wider range of frequencies 
than may otherwise be convenient. 

Communications Ferret C-1 

In cooperation with Air Transport Service 
Command at Wright Field, the Bell Telephone 
Laboratories, Inc., worked on the development 
of the first general airborne radio counter- 
measures [RCM] search installation (Com- 


munications Ferret). The initial Ferret C-1 
was a B-24-M aircraft equipped to search for 
and monitor enemy communications transmis- 
sions in the 0.55- to 300-mc band. The rear 
bomb bay was fitted with positions for three 
operators. Each operator had (1) a search 
receiver and recording attachment for auto- 
matically scanning a band of frequencies and 
recording the frequencies in use, (2) a manu- 
ally operated search receiver for monitoring 
transmissions, (3) a voice recorder for directly 
recording transmissions observed on the 
manual search receiver, and (4) a second voice 
recorder for use by the operator in dictating 
pertinent data and other information. Addi- 
tional equipment, such as panoramic receivers 
and adapters, was also provided to locate the 
frequencies of certain enemy transmissions, 
especially those which were of too small duration 
to register on the automatic recorders. The only 
DF equipment provided initially was for the 
50- to 250-mc frequency range, and there was 
no equipment for determining the polarization 
of signals. These deficiencies should be 
remedied in future Ferrets. 

The wide frequency band to be covered neces- 
sitated the use of three types of radio receivers, 
each with antennas for the particular band 
involved. In order to build a Ferret within a 
reasonable time, the receivers used in Ferret 
C-1 were of standard communication types and 
as such were not directly applicable for search 
use of the type contemplated. For example, with 
a manual search receiver of a given type on 
the same antenna, it was found necessary to 
modify the receivers to reduce radiation from 
the heterodyning oscillators in order to prevent 
mutual interference. Filters in the power- 
supply leads were also found necessary. The 
antennas also had to be designed for efficient 
operation over the band involved, and so 
located in the aircraft as to obtain reasonably 
good directional patterns. 

Several reports were prepared which give 
a general description of Ferret C-l^^® (includ- 
ing the general layout within the aircraft and 
a brief description of antennas and radio equip- 
ment used) and which discuss in some detail 
the receiver modifications found necessary for 
Ferret use.^^Q - 240 These reports contain inf or- 


TECHNIQUES 


151 


mation of interest in connection with search 
receivers in general, and indicate the short- 
comings of existing apparatus and corrective 
measures which might well be employed in 
future receivers designed specifically to meet 
search requirements. 


Countermeasures and Anti-Counter- 
measures for Radio Navigation Aids 

Radio aids to navigation direction finding 
were used extensively by the Allies and by the 
enemy, particularly in connection with the 
locating of aircraft positions during flight. 
Studies have therefore been made of the prin- 
ciples of radio navigation, including surveys of 
methods which were in use or which might 
come into use. This work provides a background 
both for general countermeasures studies and 
for more detailed consideration of counter- 
measures and anti-countermeasures for specific 
navigation schemes. 

A report-^- has been prepared which includes 
an outline and examination of the principles 
and assumptions underlying meaconing*'^ and 
other deceptive countermeasures, particularly 
with a view to specific applications. The report 
is of value both to development groups which 
are assigned the task of dealing with particular 
kinds of radio navigation schemes, and to 
tactical officers as a basis for judgment as to 
the applicability of countermeasures to situa- 
tions which develop in an operational thea- 
ter. 

The probable effectiveness of three types of 
countermeasures which might have been em- 
ployed against an h-f direction-finding system 
known to have been used by the Japanese for 
radio navigation has been investigated particu- 
larly from the standpoint of countering the 
DF system by the use of existing equipment. 
In the Japanese system in question, DF is 
conducted at land-based stations on signals 
from the plane, and information as to the 


^ Meaconing refers to the destruction of the accuracy 
of a radio navigation system by deceptive transmissions 
designed to imitate actual radio navigational aid 
signals. 


plane’s position is then communicated from a 
DF station to the plane. The report considers 
three methods of countering this system: jam- 
ming of the DF station, jamming of the plane 
reception of DF information, and meaconing. 
Use of both airborne and land-based jammers 
and meacons is considered. 


Development of Radio Direction 
Finders and Their Countermeasures 
1.5 to 100 me 

The development of a 1.5- to 22-mc aircraft 
direction finder (Type NLS-694) was under- 
taken at the request of the Army Air Forces 
to determine whether satisfactory operation of 
a low-frequency direction finder could be 
obtained on board an aircraft of size compar- 
able to the B-24 bomber. 

The equipment developed^^^ covered the fre- 
quency range from 1.5 to 22 me. It consisted 
of a remotely tuned, rotating, shielded-loop 
collector, which could be mounted at the most 
suitable location on the plane, a receiver, an 
instantaneous cathode-ray tube indicator, and 
a frequency scanner which scanned a frequency 
band 100 kc wide, centered on the frequency 
to which the receiver is tuned. The control and 
indicating units could be placed at any distance 
from the collector unit in the plane. 

Limited tests with the equipment aboard an 
Army C-45 transport plane indicated that, as 
expected, the structure of the plane itself seri- 
ously compromised DF performance at some 
frequencies and for some azimuth bearings. At 
frequencies other than the resonant frequencies 
of the plane structures, however, the errors 
were reasonably small and calibrations could 
be made to correct for the effects of the plane. 
Satisfactory performance could be secured over 
the larger part of the frequency coverage of 
this equipment. 

The NLS-694 direction finder was sufficiently 
complete that it could be delivered to Air 
Forces’ engineers for further tests aboard other 
types of planes. 

No work was performed in the frequency 
range of 20 to 100 me. 


152 


NONRADAR RECEIVING AND DIRECTION-FINDING TECHNIQUES 


7.2.4 Program of Investigation in Connec- 
tion with the Deception of High- 
Frequency Japanese Direction Finders 

Problem 

The purpose of this study was to recommend 
a field test program in connection with the 
deception of Japanese h-f direction finders in 
the frequency band 2 to 20 me. 

In order to establish these recommendations, 
it was necessary to study the available infor- 
mation on the Japanese direction finders and 
their operating setup and to coordinate this 
knowledge with the existing experience on h-f 
direction finders. 

The factors taken into consideration before 
proposing a program of work are listed herein- 
after. 

The conclusions were not too encouraging 
as far as deception proper is concerned, but it 
was possible to propose a program for decep- 
tion of the Japanese h-f direction finder after 
complete examination of the weaknesses in 
its design. 

Although the essential purpose of the study 
was to discuss deception, a comparison of the 
results expected by the three methods was 
offered. 

1. Straight jamming. 

2. Meaconing. 

3. Deception. 

Then the study was concluded with a proposed 
program.3^1 

Program Proposed 

1. Investigation of the polarization of sky 
waves within the frequency range and for the 
distances involved, using transmitting an- 
tennas properly directed and properly polarized 
for the purpose. 

2. Simultaneous development of a meacon- 
ing transmitter covering the frequency range 
and provided with means of frequency scanning 
and monitoring (in case adequate equipment is 
not readily available) . 

3. Combination of the particular transmit- 
ting antennas with the developed meacon, if 
the investigation of polarization effects gives 
satisfactory promise. If the results were not 
encouraging, the meacon would be ready to 
be used and could perform some specific work 


as such without the feature of deception by 
polarization. 

It was proposed to begin investigation of 
the meacon system before the first step men- 
tioned above was completed. 

It was further suggested that the results of 
the polarization study would be helpful even 
if straight jamming were used, since these 
results might lead to systems of jamming trans- 
mission difficult to locate with the direction 
finder. 


7.2.5 Direction-Finding Deception 
(Blanket) 

This was a system of point-to-point com- 
munication which was designed to prevent DF 
of the source of signals. The system®^ employed 
a fixed station A that masked the transmissions 
of another station B by radiating a strong 
interfering signal, usually of noise modulation. 
Communication was effected by station B, 
whose location was to be concealed, by the 
transmission of short pulses synchronously 
timed to arrive at the desired receiver in the 
short gaps between the masking radiations 
from station A. The short pulses received from 
station B were regenerated into normal Morse 
code signals which were retransmitted at sta- 
tion C on another frequency, usually fairly close 
to that of the masking station A. Thus, station 
B was able to communicate with other stations 
through the medium of station C and could 
at the same time hear station C and thus 
monitor the retransmission. At the same time 
an enemy DF station located in the vicinity of, 
or beyond, station B would be interfered with 
by the masking signals from station A and 
would be unable to take bearings on station B. 
At station B the pulses were emitted during 
the time of arrival of the masking signals at 
that point, but were so timed that they would 
arrive at station A during the gaps in the 
masking signal. The proper timing depended 
upon the delays involved in the finite velocity 
of the radio waves and accordingly varied with 
the distance between A and B. The timing 
device could be calibrated in miles and was 
simple to adjust. A full-scale demonstration 
of tj^^e system was made during the months of 


TECHNIQUES 


153 


November and December 1944. The masking 
station A and the retransmission station C 
were located in a Navy station in Trinidad. 
Station B was located on a naval ship which 
cruised off the east coast of the United States. 
These tests were very encouraging, but it was 
felt that certain improvements should be made 
before the system could be considered ready 
for use. It was felt that results would be satis- 
factory if an improvement of about 10 db could 
be made in the directive discrimination of the 
antenna on the ship so that 10 db more gain 
could be obtained in the direction of the shore 
station A. 

The Naval Research Laboratory [NRL] 
undertook to develop this directive antenna 
for the ship and tests were made with the 
antenna installed on a ship to check the direc- 
tivity of the antenna. The results of these tests 
indicated that the antenna which had been 
developed by NRL was entirely satisfactory. 
It was also planned to use two shore station 
installations covering any two of four available 
frequencies continuously. This would make it 
possible to improve security by selecting the 
highest satisfactory working frequency, since 
the highest usable frequency will tend to skip 
the zones where the enemy installations may 
be found. Equipment was developed and models 
produced for the two shore station installations, 
together with suitable improved equipment for 
the ship station. 

Some attempts were made to simplify the 
system by balancing out the ground-wave 
radiations from the masking station A at the 
near-by receiving station, leaving only radiation 
scattered back from the ionosphere. Unfortu- 
nately, although the ground wave could be 
balanced out, strong scattering due to airplanes 
flying in the vicinity made the system unwork- 
able, and the simplified system could not be 
used. 

When the signals at station B were very 
weak, it was sometimes difficult to synchronize 
the pulses properly in the gap of the masking 
signal. To overcome this difficulty, three highly 
stabilized crystal-controlled oscillators were 
produced for maintaining synchronism of the 
pulses over a reasonable period of time, with- 
out reference to the gaps in the signal radiated 
by the masking station. The stability of these 


oscillators was adequate for field tests but an 
attempt should be made to obtain greater 
stability (beyond one part in ten million) by 
refinements in adjustment and more complete 
aging of the crystal units. 

Operating and maintenance instructions^^® 
for the Blanket equipment have been prepared. 
It is understood that the Navy may possibly 
make another field test using a CV class vessel 
equipped with the unidirectional, horizontally 
polarized antenna and the improved equipment 
which were developed for this project. 

^ Electronic Tuning for Panoramic 
Reception 

A study has been made in connection with 
panoramic reception over the range 2 to 100 
me to determine the maximum f-m oscillator 
sweep obtainable by electronic means and the 
best method, principles, and limits applying to 
electronic tuning and tracking of r-f amplifier 
and oscillator stages over this range. 

Maximum Frequency-Modulated 
Oscillator Sweep Obtainable 
By Electronic Means 

Because of the importance of reactance net- 
works in the tuning of oscillators and ampli- 
fiers, an investigation®^® was made of the design 
parameters affecting the operation of reactor 
circuits. The simple, single-stage RC phase net 
was investigated, first from a simplified stand- 
point, in order to arrive at a physical under- 
standing, and then in more complex fashion, 
including all the factors having an effect upon 
the resulting reactance change. The principles 
and the method of attack used should be 
applicable, however, to a multistage net. The 
optimum values for the resistive and capacitive 
components of the phase network were deter- 
mined. 

Methods, Principles, and Limits Applying 
TO Electronic Tuning and Tracking of 
Radio-Frequency Amplifier and 
Oscillator Stages 

It was found, quite early in the investiga- 
tion ,®^2 -that an extended tuning range was 
readily obtainable by means of reactance tubes. 
The Q of the amplifier stages was, however, 


154 


NONRADAR RECEIVING AND DIRECTION-FINDING TECHNIQUES 


extremely low, and efforts were made to im- 
prove the performance. The work conducted 
toward this end included experiments intended 
to improve the Q by means of negative resist- 
ance derived (1) from the phasing of the 
reactor and (2) from the input amplifier tube. 
In both cases, the only load across the amplifier 
coil when the bias of the reactor tube was 
negative was that of the usual components plus 
that of the phase network. The Q in this case 
was normally high. When the bias of the reactor 
tube was not sufficient to obtain plate-current 
cutoff, however, additional loadings were placed 
on the coil, the most important of which was 
that due to the positive-resistive component of 
the tube impedance. This fact led to attempts 
to introduce negative resistance as an inverse 
function of negative-reactor bias. 

In the experimental work performed for the 
case in which negative resistance was derived 
from reactor phasing, it was found that an 
improved Q was obtained for the low-bias end 
of the sweep but that it was not possible to 
raise the Q at the center of the sweep without 
adversely affecting the Q at the end. 

In the case of negative resistance derived 
from the amplifier tube, the negative resistance 
was made a function of frequency and varied 
directly with it. The most important disadvan- 
tages of this method were that the derived 
negative resistance was a function of the bias 
condition of the amplifier tube and that a 
reasonable Q was not obtainable at the center 
frequency. 

In so far as tracking was concerned, it was 
found that little difficulty would be experienced 
for the usual tracking requirements, even when 
several stages were used. In the matter of the 
Q for several cascaded stages, it was found that, 
although the circuit behaved as predicted and 
the Q increased in normal fashion, only com- 
plete disregard for the complexity of the cir- 
cuits involved would warrant the use of this 
method for obtaining higher Q. 

Conclusion 

As a result of the work done on the project, it 
was felt^^^ that the most logical step for con- 
tinuance of this type of work would be to at- 
tempt to design a phase net which would have 


the proper impedance taper to effect the desired 
change in resistive components. This must be 
done, of course, with full consideration of pos- 
sible changes in reactive components. Since the 
reactive and resistive components of the phase 
net are interdependent, the results in prelimi- 
nary attempts were poor; as the proper condi- 
tion of Q was approached, the sweep width was 
reduced. 


7 3 EQUIPMENT DEVELOPMENTS 

The following section discusses specific equip- 
ments developed by Division 15 to supplement 
nonradar RCM facilities. No description is in- 
cluded here, however, of the existing items 
which were ingeniously adapted for RCM pur- 
poses. 


7.3.1 Panoramic Receiver (Panther) 

A panoramic-type receiver^^^ was developed 
to be used either for monitoring or (with suit- 
able changes) for controlling an automatically 
tuned jamming transmitter. The receiver reg- 
istered and held (without the use of persistence 
effect of a cathode-ray oscillograph screen) 
single or repeated pulses of r-f energy occurring 
in the monitored portion of the frequency 
spectrum. 

The incoming r-f pulse was converted to an 
intermediate frequency of about 30 me by 
means of a mixer and local oscillator. After 
passing through four broad-band i-f stages, a 
threshold limiter, and two amplitude-limiter 
stages, the resulting signal was introduced into 
the discriminator, which produced a d-c voltage 
proportional to the frequency deviation of the 
original r-f signal from the local oscillator fre- 
quency. This discriminator output was then fed 
into the holding circuit. 

The holding circuit was as follows. A capaci- 
tor was charged through a rectifier tube from 
the unbalance developed across the cathode re- 
sistors of two cathode-follower tubes, one of 
which had its grid grounded and the other of 
which received the input signal. The anode of 
the rectifier was connected to the capacitor. (If 


EQUIPMENT DEVELOPMENTS 


155 


the cathode of the rectifier had been so con- 
nected, the capacitor charge would have leaked 
off more quickly through cathode leakage.) 
These stages were followed by a high input 
impedance stage which was also balanced from 
cathode to cathode. The holding circuit section 
just described was repeated, using a larger 
capacitor in order to obtain a longer holding 
period. Output was taken from across the cath- 
ode resistors of a balanced cathode-follower 
stage. 

The holding circuit output caused a deflection 
on a meter calibrated in terms of the frequency 
of the original r-f signal. The deflection was held 
long enough to effect a reading before being 
manually reset to 0 with a push button. Pulses 
having time durations down to a few micro- 
seconds could thus be monitored. 

An additional output terminal from the hold- 
ing circuit permits the use of a cathode-ray 
oscillograph for observation of the envelope of 
a repeated pulse. 

This equipment was not developed beyond the 
working “breadboard’^ stage. 


Signal-Repeating Jammer (Peter Pan) 

The initial work under this project involved 
the development of a complete jamming system 
to be used against radio-controlled guided mis- 
siles [GM] . Subsequently, the scope of the proj- 
ect was redefined to cover only the development 
of a high-fidelity magnetic-tape recorder. It was 
originally believed that the enemy might use 
guided missile control signals such that con- 
ventional jamming techniques would be ineffec- 
tive. A control signal of this type, for example, 
would be one in which the phase relationships 
between a relatively large number of compo- 
nents are varied to transmit intelligence. Other 
possible signals include those in which a carrier 
is modulated at supersonic frequencies and 
those in which the carrier and the modulation 
are independently interrupted to produce sig- 
nals which cannot be easily simulated for jam- 
ming purposes. Accordingly, a signal-repeating 
jammer^^^ (Peter Pan) was to provide means 
whereby the enemy control signal could be 
recorded and retransmitted after a time delay 


calculated to cause maximum confusion. In this 
system, the enemy signals were to be hetero- 
dyned to a lower carrier frequency such that 
both the carrier and sidebands could be re- 
corded. The recorded signal was then to be 
played back after a suitable time delay and re- 
transmitted through a system including a bal- 
anced modulator, a converter to the original 
carrier frequency, and a linear r-f power am- 
plifier. 

Investigation of recording methods for use in 
the Peter Pan jammer indicated that a con- 
tinuous-loop magnetic-tape recorder offered the 
best solution, since the record could be played 
back after any desired time delay without the 
necessity of processing or mechanical adjust- 
ment. A recorder of this type having a uniform 
frequency response from 400 to 2,600 c was 
borrowed from Bell Telephone Laboratories, 
Inc., and a system was constructed and success- 
fully tested at broadcast frequencies. 

At this stage of the development, concurrent 
analysis of recorded enemy signals indicated 
the use of a relatively simple control system 
such that the signals could be readily synthe- 
sized for jamming purposes. Accordingly, in- 
vestigation of complete jamming systems was 
terminated and emphasis was placed on the 
development of high-fidelity magnetic-tape re- 
corders suitable for use with standard com- 
munications receivers to record enemy signals, 
prior to demodulation, for subsequent labora- 
tory analysis. 

A consideration of the requirements for such 
a recorder led to the decision to utilize a con- 
tinuous loop of 0.002x0.049-in. Vicalloy tape as 
the recording medium. The use of tape rather 
than wire permitted utilization of perpendicu- 
lar magnetization for recording, with the ad- 
vantage that a broader frequency spectrum 
could be recorded for any chosen tape speed. 
This reduced the requirements for the tape- 
drive and storage systems. 

A recording method was adopted in which the 
incoming signal was heterodyned to a lower 
carrier frequency which fell at the center of the 
response band of the receiver. This system of 
recording greatly improved the possible fidelity 
of reproduction by insuring the absence of dis- 
tortion, whether the phase shift through the 


156 


NONRADAR RECEIVING AND DIRECTION-FINDING TECHNIQUES 


recording system were constant irrespective of 
frequency or not. In addition, this system pro- 
vided means for determining such factors as 
carrier interruptions, type and percentage of 
modulation, duty cycle, and complex tone modu- 
lation. 

As a further means of improving fidelity, it 
was decided to utilize the so-called a-c bias 
method of recording. In this method the re- 


(XN-1) ; the second was a ship-borne equip- 
ment having a capacity of 65 sec and identified 
as AN/SRQ-2 (XN-1). 

Both these equipments consisted of a record- 
ing channel, a frequency indicator, a magnetic- 
tape recorder unit, an audio-monitor channel, a 
reproducing channel, means for generating a-c 
and d-c erase and bias currents, a modulator, a 
power supply, and various accessories. A block 



Figure 1. Block diagram of receiving equipment for signal-repeating jamming system. 


cording tape is first magnetized to saturation to 
erase any previous recording, then subjected 
to an h-f alternating field to demagnetize it, and 
finally subjected to the signal to be recorded, 
which is superimposed on an a-c bias current 
having a frequency several times the highest 
frequency to be recorded. 

Two recorder systems^^®* incorporating 
these features were produced. The first of these 
was an airborne equipment having a recording 
capacity of 15 sec and identified as AN/ARQ-12 


diagram is shown in Figure 1. The equipment is 
arranged for operation either from the 5.25-mc 
i-f output of an R-44/ARR-5 or similar receiver 
through an adapter plug or from the audio or 
video output of any suitable receiver through 
the modulator which converts such output sig- 
nals into 5.25-mc modulated signals. 

In the recording channel, the 5.25-mc modu- 
lated signal is heterodyned to a 30-kc carrier 
frequency, and both the carrier and its side- 
bands are amplified to a level suitable for 


EQUIPMENT DEVELOPMENTS 


157 


recording. A frequency indicator comprising an 
electron-ray tube and an amplifier is connected 
to the output of the recording channel and is 
arranged to produce a minimum tuning-eye in- 
dication only when the output of the recording 



Figure 2. Top view of wire recorder unit of 
receiving equipment for signal-repeating jam- 
ming system. 


channel is within 500 c of 30 kc. This indicator, 
plus a power-level meter, provided means for 
insuring a recording-channel output of the 
proper characteristics for recording. 

The output of the recording channel is ap- 


plied through a pre-emphasis network to the 
recording head of the recorder unit. This net- 
work is designed to provide constant-current 
output for input signals between 0.2 and 60 kc 
when terminated by the recording-head im- 
pedance. 

The recorder unit to which the output of the 
recording channel was applied is shown in Fig- 
ure 2. This unit includes a magazine capable 
of accommodating 122.5 ft of Vicalloy record- 
ing tape between a pair of rotatable drums. A 
drive mechanism is provided to carry the re- 
cording tape from the magazine through a 
head-plate assembly on which are mounted 
three pole-piece assemblies providing means, 
respectively, for subjecting the tape to d-c and 
a-c erase currents and to the signal to be re- 
corded superimposed upon an a-c bias current. 
The tape-drive mechanism is arranged to carry 
the tape through the head-plate assembly at 
constant speed, irrespective of variations in 
motor speed occasioned by changes in supply 
voltage or temperature, and both the lubrica- 
tion system and the lubricants used are ar- 
ranged to provide freedom from temperature 
effects. 

A single-tube oscillator included in the re- 
corder unit provides means for generating a 
160-kc a-c erase current and a 320-kc a-c bias 
current, the plate-tank circuit of the oscillator 
being tuned to 160 kc, while the cathode circuit 
is tuned to the second harmonic of the oscillator 
frequency, or 320 kc. For playback purposes, 
the signal generated by the passage of the mag- 
netized tape through the recording head is ap- 
plied to a reproducing channel which is designed 
to provide an output suitable for signal analysis 
either with a cathode-ray oscilloscope or with 
a harmonic analyzer. This channel includes a 
two-stage equalizer-amplifier having a response 
which is the inverse of that of the recorder and 
a cathode-follower output stage. 

An audio-monitoring channel comprising a 
grid-leak detector and a cathode-follower out- 
put stage may be connected either to the output 
of the recording channel or to that of the repro- 
ducing channel. This monitoring channel may 
be used for search purposes or during record- 
ing and reproducing but is not intended for use 
in signal analysis, since its frequency-response 


158 


NONRADAR RECEIVING AND DIRECTION-FINDING TECHNIQUES 


and distortion characteristics are not suitable 
for this purpose. 

The modulator, which is designed for use 
when the audio or video output of a receiver is 
to be recorded, includes an audio amplifier, a 
5.25-mc crystal oscillator, and a modulator in 
which the locally generated 5.25-mc carrier can 
be 95 per cent modulated by the input signal 
with less than 1 per cent distortion. 

The power supply for the entire equipment 
may be operated from any 110-v primary power 
source having an output frequency between 60 


output of 300 V direct current with a hum level 
of less than 10 mv. 

The above-described circuits are accommo- 
dated in three units. Unit 1, the control unit, 
includes the recording channel, the frequency 
and level indicators, the reproducing channel, 
the audio-monitoring channel, the power sup- 
ply, and the switching circuits. Unit 2, the 
recorder unit, includes the tape magazine and 
drive mechanism, the head-plate assembly with 
its three pole-piece assemblies, and the bias- 
supply oscillator. Unit 3, the modulator unit. 



Figure 3. Side view of wire recorder unit of receiving equipment for signal-repeating jamming system. 


and 2,600 c. A voltage regulator is used and 
the output of a conventional full-wave rectifier 
is applied through a single-section RC pi-net- 
work to the regulator. This regulator comprises 
two parallel-connected regulator tubes, a two- 
stage control amplifier, and a voltage-regulator 
tube which provides reference voltages. Both 
stages of the control amplifier are operated 
with fixed reference voltages obtained from the 
voltage-regulator tube, which is connected 
across the regulated output rather than across 
the unregulated input, as is usual with the 
more common regulator circuits. This power 
supply is capable of maintaining a regulated 


includes the modulator used when the audio out- 
put of a receiver is to be recorded. 

AN/SRQ-2 (XN-1) Equipment 

This equipment represents a modification of 
the previously described AN/ARQ-12 (XN-1) 
equipment to increase the recording time to 
65 sec and to fit the equipment for ship-borne 
use. Thus, the AN/SRQ-2 equipment comprises 
a Unit 1 control unit, a Unit 3 modulator, and 
a 65-sec recorder unit. As shown in Figure 3, 
the recorder unit is generally similar to Unit 2 
of AN/ARQ-12 but is of a suitable size to ac- 
commodate the required length of tape. 




EQUIPMENT DEVELOPMENTS 


159 


Accessories 

In addition to the three major units making 
up AN/ARQ-12 (XN-1) and AN/SRQ-2 
(XN-1) equipments, several accessories were 
provided. One of these was an adapter plug 
assembly arranged to replace the diode detector 
of a communications receiver and to provide a 
plug into which the detector could be inserted. 
This adapter plug assembly permits the coupling 
of the 5.25-mc i-f output of the receiver to the 
input of the recording channel. 

Another accessory comprised a rewind-reel 
assembly for use in changing tapes in the maga- 
zine. This assembly was made in two sizes, one 
for each of the two recorder units, and provided 
reels from which a fresh tape could be wound 
into the magazine at the same time as the used 
tape was removed therefrom. An additional ac- 
cessory was a lap welder by means of which the 
ends of the recording tape could be joined to 
form a continuous loop. 

Production 

Several AN/ARQ-12 (XN-1) and AN/SRQ-2 


(XN-1) equipments were produced at Airborne 
Instruments Laboratory. In addition, complete 
specifications were prepared for the use of an 
outside contractor in the production of addi- 
tional AN/ARQ-12 and AN/SRQ-2 equipments. 
Several pilot models of the AN/ARQ-12 (XN-1) 
and AN/SRQ-2 equipments were shipped to the 
United Kingdom for use in the Big Ben project.’^ 


^ Search Receivers for Proximity Fuzes 

This project involved the development of an 
improved search receiver of the panoramic type 
for use as a proximity fuze countermeasure. 
Initial requirements were coverage of a band 
extending from 75 to 230 me, continuous visual 
presentation, high stability for airborne use, 
and immunity from radar barrage jamming. 
For a description of the receiver developed, see 
Chapter 10. 

b The Big Ben project was concerned with the in- 
vestigation of possible navigational aid signals for 
V-1 and V-2 bombs. 


Chapter 8 

NONRADAR JAMMING TRANSMITTER TECHNIQUES 


81 INTRODUCTION 

A NUMBER of equipments for jamming com- 
munications and guided missiles [GM] 
were developed by the laboratories operating 
under Division 15 auspices, and a considerable 
amount of work was done in developing jam- 
mer techniques. At the same time, studies were 
made of the jamming susceptibility of various 
Allied and enemy equipments, most of which 
are discussed in Chapter 9. However, some of 
these studies bear such a close relation to the 
development of jamming equipment that they 
are discussed in this section. 

Most of the work on the development of jam- 
ming transmitters for communications and 
guided missiles countermeasures was carried 
out by the Airborne Instruments Laboratory 
(under contract OEMsr-1305), the Federal 
Telecommunication Laboratories, Inc. (under 
contracts OEMsr-285 and 936), the Radio Cor- 
poration of America (under contract OEMsr- 
895), and the Bell Telephone Laboratories, Inc. 
(under contracts OEMsr-940, 993, 778, and 966) . 
The work under these various contracts is sum- 
marized in this chapter. The research projects 
on jammers for use against proximity fuzes are 
described in Chapter 10. 


8 2 GENERAL STUDIES OF COMMUNL 
CATIONS COUNTERMEASURES 

Radio communications countermeasures is a 
broad term which includes all the various 
phases of interfering with enemy conamunica- 
tions by means of jamming, and of protecting 
friendly communications against jamming by 
the enemy. Radio communications include all 
means by which intelligence is transmitted by 
radio, that is, telephone, telegraph, direction- 
finding [DF] signals, etc. 

Jamming refers to partial or complete ob- 
structions of radio communications by means 
of radio transmissions deliberately generated 
to interfere with reception. Jamming interfer- 


ence may prevent reception by overriding 
(masking) communication signals, distracting 
the listener, disrupting the communication sig- 
nals, incapacitating the receiver, or by a com- 
bination of these means. Antijamming [AJ] 
refers to the means and methods for reducing 
the effectiveness of jamming interference. 


® Basic Considerations 

Jamming transmitters are distinguished, 
among other things, by (1) whether they are 
intended for use against communications or 
radar channels; (2) whether they are air- 
borne, ship-borne, ground-based, or expendable ; 
(3) whether they provide barrage or spot jam- 
ming; and (4) their effective output power. 

For this reason, there is a variety of jam- 
ming transmitters, each intended for specific 
applications. There may even be more than one 
type of transmitter for a given frequency band, 
each differing from the others in one or more 
of the above respects. 

Much of the following material applies equally 
well to radar jamming, and much of the mate- 
rial presented under that head in Chapter 11 
applies here. Some of the transmitters, more- 
over, can be used for both radar and nonradar 
jamming. Chapter 11 (and Chapter 10) should, 
therefore, be consulted also in this connection. 

General Jamming Problem 

The effective use of jamming requires that 
account be taken of tactical as well as technical 
considerations. For example, interception of 
enemy communications can be of considerable 
value and the use of jamming must be con- 
sidered in relation to the value of interception. 
Since jamming and interception generally can- 
not be carried on simultaneously, a decision 
must be made as to which will yield the larger 
benefits in any given situation. In general, 
lower echelon communication circuits which 
transmit orders requiring immediate action are 
good candidates for jamming, because their in- 


160 


GENERAL STUDIES OF COMMUNICATIONS COUNTERMEASURES 


161 


tercept value is low. In the higher echelons, 
where the communications concern larger and 
slower movements, interception may be of more 
value than jamming. Under certain conditions, 
jamming may be used as an aid to interception 
by forcing the enemy to repeat messages. In 
any case, jamming must be under control. Its 
unorganized use may convey information to 
the enemy, prevent desirable interception, and 
endanger friendly communications. 

An exception to the general philosophy of 
limiting jamming transmissions as much as 
possible would be in an instance in which a false 
appearance of activity is to be created. If the 
enemy came to associate jamming operations 
with increased activity, it might be desirable, 
upon occasion, to operate jammers deliberately 
for deception and confusion purposes. 

From a technical standpoint the jamming 
problem is one of disrupting enemy communi- 
cations with a minimum of equipment and per- 
sonnel. To jam an enemy communication signal 
completely requires that his receiver be bom- 
barded with jamming energy about equal to, 
or greater than, the energy in his signal. The 
amount of jamming power required depends on 
the power radiated by the enemy transmitter, 
the location of the jammer with respect to the 
enemy station, the radiation characteristics of 
the jamming and victim systems, and other 
factors. The effectiveness of jamming power 
can be increased by concentrating it on the 
receiver by means of a directive antenna or by 
locating the jammer so as to obtain favorable 
propagation conditions, as in aircraft. 

Scope of Activities 

The broad picture given above will serve to 
indicate that effective jamming requires con- 
sideration of a wide variety of technical prob- 
lems, including such factors as (1) propagation 
of radio waves (discussed in Chapter 6), (2) 
relative effectiveness of various types of jam- 
ming interference, (3) effect of receiver char- 
acteristics on effectiveness of jamming signals, 
(4) the choice between spot and barrage jam- 
ming, (5) design of jamming transmitters (see 
also Sections 8.3 and 8.4), (6) antenna effi- 
ciencies and directional characteristics (dis- 
cussed in Chapter 4), and (7) integration of the 


various elements into a jamming system. Since 
in any jamming system it is necessary to select 
the channels to be jammed, there is also the re- 
lated problem of searching, observing whether 
jamming is effective, and in some cases direc- 
tion finding to locate the source of the enemy 
signals. The general receiver problem is dealt 
with in Chapter 7 ; but certain receivers which 
form integral parts of complete jamming 
systems are described here (Sections 8.3 and 
8.4). 

Theoretical analyses have been made and 
considerable information gathered on all these 
subjects by laboratory investigations and field 
tests. In this program, the contractors have 
been guided by consultation with the Armed 
Services and participation in various Office of 
Scientific Research and Development [OSRD] 
committee meetings, by analyses of intelligence 
reports which were made available, and by par- 
ticipation in Army maneuvers in this country 
involving the use of radio countermeasures 
[RCM]. In addition, through experienced RCM 
personnel supplied for service abroad for vari- 
ous periods, a knowledge of theater problems, 
conditions, and requirements has been acquired. 
(See Chapters 14 and 15.) 

As the work progressed, individual reports 
on various phases of the jamming problems 
have been issued. This information was re- 
viewed and the more important findings used 
in the preparation of Division 15 RCM Hand- 
book No. U on the jamming and antijamming 
of radio communications.^^® This consists of the 
following parts: Part I “Jamming and Anti- 
Jamming of Radio Communications — An Intro- 
ductory Survey of Technical Considerations,^’ 
Part II “Estimating the Performance of Radio 
Telephone Jamming Systems,” and Part III “Es- 
timating the Performance of Radio Telegraph 
Jamming Systems.” The handbook, supple- 
mented by other reports,^®^ contains a large 
amount of the useful technical information at 
present available on the subject of communica- 
tion jamming and therefore constitute basic 
reference material for systems studies. A large 
part of the background material for these refer- 
ence handbooks was provided by the various 
reports issued under contracts OEMsr-778, 
940, and 966.®®*^'^’ 167-246 More specific refer- 


162 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


ences to many of these reports are given at the 
appropriate points below. 

8.2.2 Types of Jamming Modulation 

The type of modulation employed for jam- 
ming purposes depends upon whether a tele- 
graph, telephone, or radar channel is being 
jammed, upon whether spot or barrage jam- 
ming is being employed, upon the vulnerability 
of the victim receiver to various types of mod- 
ulation, and upon the kind of modulation that 
can be produced at the carrier frequency and 
power output of the jammer. 

In the jamming of communications channels, 
one consideration in the choice of type of mod- 
ulation is the psychological reaction of an 
operator to novel forms of interference. The 
modulation may be chosen to distract the lis- 
tener rather than to obliterate the desired sig- 
nal. This technique is of particular importance 
when the jammer lacks sufficient power to mask 
the victim signal, since even a weak distracting 
signal may succeed in preventing the reception 
of any great amount of intelligence. In addition 
to the studies reported below, many investiga- 
tions of the effectiveness of various jamming 
signals have been made from the AJ point of 
view and are discussed in Chapters 9 and 13. 

Audio Waveform Requirements 

Under contract OEMsr-626, an investigation 
was made of the effectiveness of various a-f 
noises in masking speech and telegraphy, and 
the reports provide an excellent introduction 
to the audio requirements of jamming.^® -^ It 
was concluded that in the final audio circuits the 
interfering wave should be continuous in both 
frequency spectrum and time, that gaps in fre- 
quency or time should be made as small as 
possible, and that noises having the properties 
of audio-resistance noise are especially effec- 
tive.^®- 

Radio Waveforms 

With regard to the r-f output of a communi- 
cations jamming transmitter, it may be said 
that in barrage jamming, and probably in any 
other kind, the ideal type of signal is the one 


characterized by the greatest disorder. One way 
of looking at the effect of the output jammer is 
as follows. 

Any disturbance whose spectrum falls com- 
pletely in a band of frequencies small in width 
compared with the mean frequency can be rep- 
resented as 

fit) cos [coof + (1) 

where f{t) represents the envelope of the am- 
plitude, coo is the mean frequency, and cf>(t) is a 
varying phase term whose time derivative is 
the instantaneous angular frequency. Both / 
and <j> may vary in time, in a manner related to 
the width of the spectrum. 

Amplitude Modulation. There are two ways 
of introducing disorder into expression (1). 
Suppose first that <j>(t) is held invariant with 
time and f(t) is modulated between zero and 
some positive value. This is recognized as am- 
plitude modulation and gives a spectrum con- 
sisting of a carrier plus upper and lower side- 
bands. It might be represented as a vector of 
fixed phase and changing length, having con- 
stant frequency coo and phase <t>. If f(t) has a 
uniform spectrum up to a limiting frequency 
and zero above it, the double sideband will have 
a uniform spectrum over twice the frequency 
width. The carrier represents energy without 
disorder and would not be expected to be effec- 
tive in jamming. Its power is more or less 
wasted, and the carrier might better be elim- 
inated if its presence makes difficult the pro- 
duction of maximum sideband power. 

This double-sideband type of signal with 
carrier eliminated — direct-noise amplification 
(Dina) — has been used and is a very efficient 
type. It may be objected that the two sidebands 
are not really independent, since the phase 
relations are such that in a vector diagram the 
vector would travel a straight line centered 
at the origin. This is true if the receiver is 
tuned exactly to the suppressed carrier — a 
situation which is hardly likely to arise in 
practice. 

Frequency Modulation. A second method of 
introducing disorder is to hold f(t) constant 
and let <^(0 or d<f>/dt vary. This is phase or 
frequency modulation and can be made to give 
a uniform spectrum over an r-f band. That 
uniformity of spectrum does not tell the whole 


GENERAL STUDIES OF COMMUNICATIONS COUNTERMEASURES 


163 


story is very clear here. As a function of time 
d<f>/dt might be made up wholly of very 1-f 
components so proportioned as to make the 
r-f spectrum desirably flat; yet for jamming the 
result might be poor because the instantaneous 
frequency dcf>/dt passes through the band of 
the receiver so infrequently that amplitude 
limiting of a crude type becomes a very effec- 
tive AJ measure. To avoid this, it is desirable 
as a minimum to insure that the instantaneous 
frequency will sweep through each channel 
often enough to prevent the transient in the 
receiver from decaying below the level of com- 
munication signal. As an oversimplified ex- 
ample, if the receiver comprised a single r-f 
tuned mesh having a half-power bandwidth 
A/ equal to 5,000 c, and a time constant 1/xAf 
sec, we would require about xAf crossings per 
second, so that the modulation frequency would 
need to be x\f/2 to meet the condition at the 
middle of the barrage. Actually, it is probably 
preferable to provide a more rapid rate, so 
that transients from several sweeps coexist 
in the tuned circuits. The fundamental point 
is that the spectrum is only half of the story 
and that true randomness does not exist in a 
spectrum in which spectral components are 
connected by some special phase patterns, such 
as is required to give the envelope a constant 
amplitude. 

Sideband Energy Distribution. A knowledge 
of the distribution of energy in the sidebands 
of a modulated jamming transmitter is essen- 
tial in planning the details of tactical applica- 
tion of the jammer, especially in barrage jam- 
ming. This is particularly true when a number 
of transmitters must be used to cover the band 
of frequencies involved. As detailed below, the 
distribution of sideband energy considerably 
influences the manner of setting the carrier 
frequencies of the various transmitters in- 
volved in a barrage operation of this type. 
Information concerning the distribution of the 
sideband energy is also vital to calculations of 
the effectiveness of a jammer for protecting a 
given target against a specific radar. 

Theoretically, the distribution of energy in 
modulation sidebands is confined to specific 
frequencies when recurrent waveforms are 
used for the modulation. Consequently, there 


are likely to be gaps in the spectrum. The 
widths of these gaps are a function of the 
parameters involved, and, under some circum- 
stances, such types of modulation may be en- 
tirely unsatisfactory for the purpose. 

In practice, the actual distribution of side- 
band energy may differ considerably from the 
theoretical values because of the characteristics 
of the electrical circuits involved. For example, 
there may be a considerable amount of inci- 
dental frequency modulation of the carrier. 
Under these circumstances, as compared to the 
theoretical distribution, there are relatively 
large amounts of energy spread over a con- 
siderable band in the vicinity of the carrier 
frequency. A transmitter having incidental 
frequency modulation of the carrier is more 
effective in jamming receivers close to the 
nominal carrier frequency than if the frequency 
modulation were not present. The incidental 
frequency modulation allows the carrier energy 
to be effective in jamming, even though con- 
tinuous-wave [c-w] AJ devices may be in use. 

Random Noise 

The search for disorder leads one naturally 
to noise, which deserves special emphasis. Noise 
is random both in amplitude and in instan- 
taneous frequency and so can be considered 
the acme of disorder. It has a uniform spectral 
distribution of energy, except as it may be 
influenced by the circuit elements. As the bar- 
rage bandwidth is widened, the spectrum of the 
envelope f(t) and that of the phase term 
<ji(t) in expression (1) will be widened in pro- 
portion. Since noise has no periodically recur- 
ring frequency, it cannot be filtered out or 
otherwise eliminated without also removing 
the desired signal. This is a description of 
thermal noise, which is the basic factor limiting 
the sensitivity of any receiver. Thermal noise, 
therefore, has come to be regarded as the ideal 
type for jamming. 

Noise has another attribute that makes it 
a desirable type of jamming modulation. This 
is the fact that the presence of a noise jamming 
signal in a receiver may not be recognized as 
deliberate jamming. It is, therefore, a subtle 
type of jamming that may be practiced for 
some time, upon the uninitiated, before being 


164 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


recognized for what it is. There is, however, 
another factor to be considered in this respect, 
particularly in the jamming of communica- 
tions channels. Many operators are experienced 
in listening through background noise and 
therefore have less difficulty in adjusting them- 
selves to this form of interference than to 
stepped tones or some other novel form of jam- 
ming. Furthermore, an inexperienced operator 
is prone to stop listening when he hears peculiar 
interference or realizes he is being jammed. 
With noise jamming, not realizing he is being 
intentionally jammed, this operator continues 
to copy or try to copy. These factors are vari- 
able, however, and to some extent are transient 
in nature and should be considered as such. 

The ideal nature of thermal noise, therefore, 
cannot always be accepted without reservation. 
Thus, in the reception of c-w telegraphy, sup- 
pose that normal reception employed a beat 
note of 500 c. The information for slow hand 
speeds would then be delivered in a narrow 
band about 500 c. To jam normal reception it 
would be best to put all the power into a 
similarly narrow band of resistance noise 
clustered around the radio carrier. Unquestion- 
ably, this would be very effective if the com- 
munication carrier frequency could be followed 
that accurately, but, as a practical matter, we 
might have to use a band of, for example, 1,000 
c. It has been found, under some circumstances, 
that if the receiving operator turns off his beat- 
frequency oscillator, the telegraph signal can 
be read as a small but perceptible modulation 
of the thermal noise itself. In other words, 
each small band of thermal noise acts like the 
beating oscillator itself. In this case, it is 
desirable that the thermal noise be given an 
additional strong modulation, itself random in 
character, and in the same frequency range 
as the signal to be jammed. 

A disadvantage of noise modulation, from 
the equipment point of view, is the possible 
difficulty of generating the desired amount of 
noise-modulation power, particularly at the 
higher frequencies and at the higher output 
levels. (See Chapter 2 on noise sources.) 

Clipped Noise. When random noise is clipped 
at the top, the spectrum retains its continuous 
character but is changed in shape. When the 


clipping occurs at a level very low compared 
with the effective value before clipping, a con- 
stant amplitude exists most of the time and 
the waveform tends toward that of a constant 
amplitude which is frequency-modulated. Thus, 
this constant amplitude exists about 90 per cent 
of the time when clipping is at 30 per cent of 
the effective amplitude. 

Underclipping, on the other hand, accentu- 
ates the pulse peaks, in some ways giving the 
effect of noncoherent pulses. It is apparent that 
this must not be carried so far as to lead to 
overly long silent intervals. This becomes espe- 
cially important as the width of the barrage 
band is decreased, since the intervals of silence 
will then increase and may become dangerously 
large. Class C amplifiers produce this effect 
and must therefore be avoided in narrow bar- 
rages. On the other hand. Class C amplifiers 
may safely be used when the width of the 
barrage is very great compared with the band 
of the victim receiver. 

Other Modulations 

Various forms of modulation other than noise 
are used for jamming, particularly for special 
purposes. In many cases, however, other modu- 
lations are more effective than random noise 
even for communications jamming, as indi- 
cated above, because of power or bandwidth 
considerations. Some of the commoner types 
are as follows. 

Continuous Wave. The use of an unmodulated 
carrier (c-w) for jamming may be effective in 
communications channels but will have little 
or no effect upon well-designed radar receivers. 
To be effective against telegraph channels 
operated by skilled personnel, the c-w jamming 
signal must be accurately tuned, so that the 
difference in frequency between the desired 
and undesired signals is within 2 to 10 c, and 
must be keyed at the same rate or slightly 
faster than the victim signal. 

In telephone channels the intermodulation 
products that result from the presence of an 
undesired c-w carrier can also be effective in 
preventing the reception of intelligence. The 
optimum difference in frequency between the 
desired and the undesired carrier for maximum 
jamming is in the vicinity of 500 c. It is to 


GENERAL STUDIES OF COMMUNICATIONS COUNTERMEASURES 


165 


be noted that, in the two types of communica- 
tions channels mentioned, c-w interference is 
effective only in spot jamming and then only if 
present in sufficient strength and if accurately 
adjusted to the optimum relative frequency for 
jamming. 

Sine-Wave Modulation, If the carrier is 
modulated by a sine wave, the jamming will 
sound like a pure tone in the receiver. This 
is a relatively ineffective form of jamming by 
itself and requires considerably more jamming 
power than noise, for instance. When the fre- 
quency of the modulation is varied, however, 
the effectiveness is greatly increased.^^^ In some 
forms, the variation is in steps (Bagpipes), 
whereas in other transmitters it is continuous. 

Noncoherent Pulses. Another special example 
of waveform consists of noncoherent pulses.^^^ 
First consider an isolated rectangular pulse of 
radio frequency, having a duration of 1 psec 
and an instantaneous frequency of 100 me. The 
Fourier integral shows its spectral shape to be 
the familiar sin x/x shape with zeros at 99 
and 101 me. About the maximum (100 me), 
the spectrum is fairly flat. In a series of these 
pulses at regular or irregular periods of the 
same or equal amplitude, the shape of the 
spectrum remains unchanged, provided that 
there is no relation between the phases of suc- 
cessive pulses. If there is a phase relation such 
that the oscillations appear to be merely sec- 
tions of the same sine wave, the spectrum is 
altered. A large amount of energy appears in a 
carrier at the middle of the spectrum, and the 
whole spectrum may become bumpy. In particu- 
lar, if there is a periodic repetition of equal 
pulses, such phase interdependence leads to a 
line spectrum instead of a band spectrum, the 
lines being separated by a frequency equal to 
the pulse frequency. The pulses are then said to 
be coherent in phase ; without phase dependence 
they are called noncoherent. 

This is a form of noise having much to 
recommend it but also having its definite limi- 
tations. Its advantages have to do with the 
ease of producing acceptable powers in simple 
and easily maintainable apparatus ; its dis- 
advantages, with the difficulty of obtaining a 
sufficiently high pulse rate to jam wide-band 
receivers. Difficulty is to be expected when the 


period between pulses exceeds the time con- 
stant of the receiver or is of the same order. 
It would be preferable to have this period 
considerably less than the receiver time con- 
stant. 

Selection of Modulation Waveform 

There are a great many factors involved in 
selecting the most effective waveform for the 
modulation of a jamming transmitter, includ- 
ing the characteristics of the receiver to be 
jammed. These factors are discussed in detail 
in Section 8.2.3, where references are given 
to reports comparing the vulnerability of vari- 
ous receivers and the effectiveness of various 
jammers. Reports are available also on the 
relative effectiveness, in general, of the various 
types of jamming signals.®^* 

Because of the growing use of limiting circuits 
and other devices for giving AJ protection to 
receivers, the selection of the best waveform 
in future work on jamming transmitters is a 
matter of increasingly great importance. 


8.2.3 Effectiveness of Jamming 

As is seen in Section 8.2.2, a wide variety of 
types of interference have been used or pro- 
posed for use, such as steady carrier, keyed 
carrier, and carrier which is modulated in 
amplitude or frequency by a single frequency, 
by resistance noise, by a sawtooth wave, or 
by a series of tones (Bagpipes). Sweep types 
of jamming may consist of mechanical fre- 
quency modulation, either smooth or jittered. 
Additional types of interference are buzzer 
(spark), directly amplified resistance noise, 
carrier-suppressed (sideband) transmission, 
and pulses. 

Since the characteristics of various radio 
systems differ, some types of radio circuits are 
more vulnerable to a given type of jamming 
signal than others. Tests of jamming effective- 
ness therefore involve the evaluation of com- 
binations of jammer and communication set 
characteristics. Such tests are best made on 
the actual equipment under controlled labora- 
tory conditions. These tests should be supple- 


166 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


merited by such flight tests as are required to 
check the mechanical operation of the jamming 
equipment and to determine the radiated power 
in various directions when the jammer is 
loaded into its recommended antenna. However, 
it should not be necessary to make airborne 
jamming tests of each jammer against every 
known or projected enemy communications 
link. Instead, jamming results during airborne 
tests against a receiver of known character- 
istics can be applied to other receivers when 
their jamming susceptibility has been deter- 
mined in the laboratory. 

Vulnerability of Receivers 

Through poor design, some receivers may be 
very vulnerable to some simple form of modula- 
tion. Since it is often possible to obtain larger 
power outputs and relatively simple design 
when simple types of modulation are employed, 
such shortcomings of enemy equipment should 
be exploited. At the same time, the ease with 
which these weaknesses may be corrected must 
also be borne in mind, since the useful life of 
any offensive RCM device depends upon how 
difficult it is to devise an antidote and put it 
into service. As an example of this, it is to be 
noted that some receivers may be made less 
vulnerable to simple types of jamming signals 
simply by manipulating the volume controls 
in what might be considered an abnormal 
manner. 

Although tests may indicate that a given 
receiver is particularly vulnerable to a certain 
type of modulation, it does not necessarily 
follow in practice that this type is the best to 
use. In determining the best type, it is neces- 
sary to give consideration to the practical 
aspects of employing this type of modulation in 
an actual transmitter. For example, one type of 
modulation may be twice as effective as an- 
other; yet it may be possible, with a given 
amount of input power, to obtain four times as 
much output with the less desirable modulation. 
Under these circumstances, use of the latter 
may be indicated. 

Tests of Jamming Effectiveness 

Jamming is no exception to the general rule 
that progress in engineering development de- 


pends upon measurement. Methods were devised, 
therefore, for assessing the effectiveness of 
jammers of various sorts, expressing it in such 
terms as to facilitate analysis and make possible 
the intelligent statement of barrage require- 
ments. The practice was to produce a modulated 
signal, to measure samples of signal and of noise 
separately, and to attenuate them separately to 
significant reception levels. The samples were 
then mixed and impressed on the receiver to be 
jammed. Obviously, good shielding was needed 
(see also Chapters 9 and 13). 

Test Techniques and Procedures. There was 
little background of experience to draw on for 
this type of work, either from the standpoint of 
measuring technique or definitions of terms to 
be used in evaluating and comparing perform- 
ance. One of the early and continuing phases of 
the work was the evolution of a good laboratory 
setup and test procedure, involving the con- 
struction of shielded rooms, special apparatus 
for simulating radio-transmission paths, and ap- 
paratus for producing many types of signals. 
Some of the more complete block diagrams of 
the test and shielding arrangements and dis- 
cussions of test methods are given in various 
reports-^-’ 232, 237 Chapter 5) . 

With respect to standardization of definitions 
and testing procedures, a committee cooperated 
in the preparation of a report-®- outlining the 
methods of testing jamming effectiveness in 
use. This report is good reference material for 
an understanding of the various terms used in 
the individual reports issued on this subject and 
should be of considerable value to others who 
may enter this field. 

Some 20 different types of a-m and f-m jam- 
ming signals were used in the laboratory in 
evaluating jammer performance and receiver 
vulnerability from the standpoint of both tele- 
phone and telegraph communications. Some of 
these were simulated jamming signals ; in other 
cases actual jamming apparatus was used. Tests 
of receiver vulnerability were made not only on 
American sets of the types commonly used but 
also on a number of captured German and Jap- 
anese radio receivers. Knowledge of the per- 
formance of American sets was needed not only 
for developing AJ techniques but also for de- 
termining their vulnerability relative to enemy 


GENERAL STUDIES OF COMMUNICATIONS COUNTERMEASURES 


167 


sets, in order to avoid jamming our own re- 
ceivers in areas where jamming is used against 
the enemy on a fluid front. 

Results of Tests. The results of these meas- 
urements are given in many reports on the 
speciflc pieces of apparatus concerned.^ Some of 
the more important general conclusions found^"^^ 
are as follows: (1) With suppressed-carrier, 
really carrierless (Dina) noise, jamming of a 
carrier with high percentage amplitude modu- 
lation occurs when the noise accepted over the 
speech sideband spectrum is about equal to the 
carrier power. (2) One source of noncoherent 
pulses and two f-m jammers were each 1 or 2 
db less efficient in jamming a narrow-band a-m 
receiver than the Dina, when all of these were 
used so as to give noise-type interference. 
(3) All superregenerative receivers tried were 
very susceptible to Dina noise and required 
some 14 db less noise power per kilocycle of r-f 
band at the jamming point than the narrow- 
band receiver; for one f-m receiver this figure 
was 10 db. (4) One American superregenera- 
tive receiver was as easily jammed by non- 
coherent pulses as by Dina noise. (5) A Jap- 
anese type of superregenerative receiver which 
had broader band characteristics than the 
American was about the same in susceptibility 
as the narrow-band receiver when the pulse 
rate was sufficiently high (80,000 pulses per 
second) . 

Jamming Power Requirements 

In general, it is desirable to employ as much 
jamming power as possible. As a practical mat- 
ter, however, the weight, bulk, portability, and 
power drain of the equipment often determine 
the size of the transmitter that can be used. 
Furthermore, it is not economical on any score 
to provide jamming transmitters that are ap- 
preciably larger than necessary to accomplish 
the desired end. 

A discussion of the exact mathematical re- 
lationships whereby the jamming power may 
be calculated for a specific case is beyond the 


a References 65, 174, 196, 207, 211, 212, 217, 219, 221, 
224, 226, 228, 229, 232, 233, 236, 255, 257-261, 263-268, 
270-281, 283-287. Summaries of this type of informa- 
tion, including the results from some of the references 
listed above, are given in reference 345. 


scope or intent of this book, but the manner in 
which the various factors involved influence the 
jamming power requirements is outlined below. 
A knowledge of these relationships is of con- 
siderable value, since, if the performance of a 
given jammer against a given enemy system is 
known, an accurate estimate can thus be made 
as to its performance under slightly different 
conditions. 

In the jamming of communications channels, 
line of sight between the jammer and the victim 
receiver seldom exists (as it often may in radar 
jamming), with the result that it is generally 
necessary to take into consideration the effect 
of the earth upon the propagation of the jam- 
ming signal. Because of the large number of 
parameters involved, this can be done readily 
only by reference to propagation curves that 
have been prepared for the particular values of 
frequency, soil conductivity, dielectric constant, 
and transmitter and receiver antenna height in- 
volved (see Section 6.3.2). 

Other factors being equal, the power required 
to jam a communications channel is (1) directly 
proportional to the power output of the victim’s 
transmitter, the power gain of the associated 
antenna, the discrimination of the receiving 
antenna against the jamming signal, and the 
jam-to-signal [J/S] ratio for the type of re- 
ceiver and modulation involved; and (2) in- 
versely proportional to the power gain of the 
jammer antenna in the direction of the victim’s 
receiver. 

It is evident that, in order to calculate the 
effectiveness of a jammer accurately, consider- 
able information, some of it concerning the 
victim’s equipment, must be available. It is pos- 
sible under some circumstances, however, to 
make use of a comparison method that will 
often give sufficiently accurate results to be 
useful. This method consists of setting up a 
receiving site where the relative value of the 
victim and the jamming signal can be deter- 
mined and then, from a knowledge of the loca- 
tion of the enemy receiver and the jammer, 
calculating the estimated effectiveness of the 
jamming. Although this method also involves 
the use of wave-propagation curves, it does not 
require so much detailed information concern- 
ing the enemy equipment. 


168 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


^ Barrage versus Spot Jamming 

There are two ways in which one can ensure 
that all the communications channels of im- 
mediate interest are jammed. The barrage- 
jamming method is to spread the jamming 
energy over a frequency band wide enough to 
neutralize a number of channels simultaneously, 
so as to be certain of blanketing the victim 
channels. Contrasted to this is spot jamming, 
in which the transmitter is tuned to exactly the 
same frequency as the victim signal and the 
jamming energy is concentrated in a frequency 
band just wide enough to neutralize one channel 
adequately. Each of these methods has ad- 
vantages of its own. 

Comparison between the Methods 

Spot jamming requires the use of as many 
transmitters as there are channels to be 
jammed and also the attendance of skilled op- 
erating personnel. On the other hand, in jam- 
ming communications channels, the presence of 
an operator is usually desirable in any case for 
identification of the victim signals. Under some 
conditions, however, the enemy frequencies may 
be well known and well separated from friendly 
ones, so that continual identification is unneces- 
sary; in such circumstances, a barrage jammer 
can be preset and simply switched on when the 
jamming is begun. Moreover, because of the 
broad band covered, a barrage jammer can be 
set less carefully to start with but has the dis- 
advantage that it prevents the use of many 
channels for friendly communication, except 
where the jamming is done deep in enemy terri- 
tory (from aircraft, for instance). 

With barrage jamming, where the energy 
is spread over a large part of the spectrum, 
the interference will blanket any unused chan- 
nels intervening between active ones. Although 
this condition prevents the enemy from re- 
establishing the communications by minor 
shifts in frequency, it is wasteful of power, so 
that an accurately tuned spot jammer, which 
concentrates its energy in the most effective 
way, requires less power than a barrage jammer 
against individual or widely spaced communica- 
tions channels. When there are a large number 
of channels within the barrage band, however. 


an equally large number of spot jammers (no 
matter how powerful) is needed to cover them, 
even though a comparatively small number of 
barrage jammers of equal power might be suf- 
ficient. That is, in some circumstances a spot 
jammer can waste power by concentrating far 
more than is needed at a single frequency, 
whereas at other times the barrage jammer 
wastes it by spreading it too far. 

The type of modulation used for spot jam- 
mers should be such that the bandwidth of the 
jammer exceeds that of the victim channel by 
an amount only sufficient to allow for inac- 
curacies in aligning the jammer with the victim 
signal and for the frequency drift of the jam- 
mer and the victim channel. Barrage jammers 
should be provided with a form of modulation 
that distributes the energy evenly over the band 
of frequencies that is being barraged. In gen- 
eral, a random type of modulation is more 
effective than a periodic type, since in many in- 
stances AJ measures may be taken to cope with 
the latter kind of interference. 

Frequency Setting of Barrage Jammers 

As contrasted with spot jammers, barrage 
jammers can usually be preset to the proper 
frequency band, and, in the case of airborne 
equipment, the attention required during a 
flight can thus be reduced to simply turning 
the equipment on and off at the proper time. 

In the jamming of communications channels 
the procedure for setting the jammers on fre- 
quency is merely to make certain that the 
barrage completely covers the band of fre- 
quencies to be jammed. In large formations, 
however, where many jammers are available, 
it is important that their frequencies be 
accurately adjusted so that the maximum pos- 
sible number of channels are occupied by the 
jammer carriers. This may be done by carefully 
spacing the carriers uniformly across the band 
occupied by the enemy systems. Under these 
circumstances the carriers, particularly if they 
have incidental frequency modulation, con- 
tribute greatly to the jamming effectiveness. 
In an operation of this kind, the absolute 
accuracy of the frequency meter used for set- 
ting the carrier frequencies need not be very 
great, since only the relative accuracy is im- 


GENERAL STUDIES OF COMMUNICATIONS COUNTERMEASURES 


169 


portant, particularly if it is possible to check 
all transmitters against the same frequency 
meter. 

Frequency Setting of Spot Jammers 

If the jammers are otherwise in good operat- 
ing condition, the success of any plan of 
jammer activity depends entirely upon the 
accuracy with which the transmitters are 
adjusted to the victim frequency. In the manu- 
ally adjusted transmitters used for spot jam- 
ming, therefore, means must be provided for 
determining the victim frequency and for 
accurately adjusting the jammer to this 
frequency. An operator trained to identify the 
intended victim signals and to adjust the jam- 
ming transmitter is also required. 

In spot jamming, the jammer carrier must 
be set as closely as possible to the frequency 
of the victim signal. In ground-based or ship- 
borne equipment this does not present a serious 
problem since ample equipment and operating 
personnel can generally be made available. In 
airborne installations, on the other hand, the 
need for conserving weight and personnel 
makes it desirable to preset the jammer to the 
proper frequency on the ground before take-off. 
Unfortunately this cannot be done to spot 
jammers, because of the setting accuracy that 
is required. Deviations introduced by receiver 
or frequency meter calibration inaccuracies, by 
reading and resetting errors, and by frequency 
drifts in both the frequency meter and the 
transmitter because of changes in temperature, 
pressure, humidity, and power-supply voltages, 
all combine to make it impractical to preset 
spot jammers. The accuracy required depends 
upon the type of jamming used and ranges 
from a few cycles per second in keyed c-w 
jamming to 0.5 me or so in radar jamming. 
Overall accuracies of 0.1 per cent or consider- 
ably better are evidently necessary. 

Even though it may not be feasible to preset 
an airborne spot jammer, the equipment should 
be adjusted before take-off as closely as possible 
to the frequency to be jammed. To make a 
major frequency change in the air is generally 
difficult and time-consuming. Furthermore, by 
setting up the equipment as nearly as possible 
to the desired frequency, the performance of 


the set can be accurately checked at approxi- 
mately the frequency at which it will be used. 

The accuracy of setting required for spot 
jamming necessitates the use of a “setting-on’^ 
receiver, which thus becomes an essential part 
of the jamming system. This is especially true 
for automatic-search and lock-on systems, in 
which the receiver is automatically swept in 
frequency until a signal is picked up, where- 
upon the jamming transmitter is switched on 
and tuned to the frequency indicated by the 
receiver; in this way, the need for a special 
operator is eliminated. Such receivers, which 
are integral parts of jamming systems, are 
described in the succeeding sections of this 
chapter rather than in Chapter 7, where the 
general receiver problem is discussed. 


® Design of Jamming Transmitters 

In the following paragraphs are discussed 
general methods and techniques in the design 
and development of jamming transmitters. 
Details on specific jammers and associated 
equipment are given in Sections 8.3 and 8.4. 

Frequency-Modulation Methods 

A number of different systems for producing 
frequency modulation were considered and 
tried experimentally. In most cases, the aim 
was to produce a random modulation of some 
sort, generally by noise from an external source 
(see Chapter 2). Both electronic and electro- 
mechanical methods were developed, as well 
as an unusual ferromagnetic system. 

Frequency -Modulation Jamming Produced 
Electronically. A frequency-modulation jammer 
was developed in which the method of modula- 
tion was electronic.^®^ Reactance tubes were 
used to produce the modulation, the modulating 
signal being random noise derived from a gas- 
tube noise source (Gaston). Modulation was 
followed by harmonic generation and amplifi- 
cation to 100 or 200 w. This method of opera- 
tion was considered for many applications. 

The simplest apparatus of this kind would 
consist of a power oscillator which fed an 
antenna directly. For the purpose of design, 
the volt-amperes required in reactance tubes 


170 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


must be known. These reactive volt-amperes are 
of the same order as the power dissipation 
required in the reactance tubes, provided that 
the frequency modulation is linear. Then if 
the oscillator tube provides a constant rms a-c 
voltage e across the main condenser, the 
reactive volt-amperes to be provided elec- 
tronically are 2e2CAa), independent of the mean 
frequency co. Assume, for example, two similar 
tubes in parallel, one as an oscillator and the 
other as a reactor. A 10-kw tube might have a 
total capacity C (both tubes and circuits) of 
the order of 100 ^^f, and e might be 6,000 v; 
substituting these values in the equation 
— 10 kw then gives a A/ of approxi- 
mately 220 kc. This crude estimate indicates 
that wide barrages require reactance tubes of 
very high ratings if the frequency is to be 
modulated in the final stage. A promising 
‘‘switching’’ method^®^ which was investigated 
seems to warrant further research. 

Electromechanical Frequency-Modulation 
Jammers. Another frequency-modulation 
method which has some interest is based on 
electromechanical frequency variation. This 
was accomplished by the use of a condenser 
whose capacitance could be made to follow the 
rapid and irregular changes of random a-f 
noise, through the use of a diaphragm driven 
by a loudspeaker mechanism. The condenser 
thus formed is used as one of the tuning ele- 
ments of an oscillator, so that the signal 
produced varies in frequency at random rates 
and amounts from the mean or carrier fre- 
quency. This type of interference was highly 
effective against a-m receivers, at least against 
those not utilizing limiters. Powers of 300 to 
500 w at a bandwidth of 2 me in the range 
from 20 to 37 me were obtained under labora- 
tory conditions. Considerable development 
would have been needed to perfect the special 
electromechanical device used, because voltage 
breakdown was encountered in pushing the 
frequency swing to the extremes required in 
barrage work. Nevertheless, the method might 
prove to have a natural adaptability where 
relatively narrow bands suffice.^®® 

Frequency Modulation. In the course of 
research on expendable jammers (see below), 
a method of frequency modulation was de- 


veloped which is thought to have applications 
elsewhere.i”^® The method depends on the change 
of inductance of a coil with a Permalloy core 
when the magnetization is varied. In order to 
overcome the low Q of the Permalloy coil, posi- 
tive feedback was used around two stages of 
amplification instead of the usual single stage. 
As a result, large changes of frequency could 
be effected merely by varying the core mag- 
netization, which required a relatively small 
amount of modulating power. A second advan- 
tage was the absence of the critical 90-degree 
phase circuits which are needed in most f-m 
systems. A unit capable of producing 10 w of 
radio noise power was built and tested. Ex- 
pendable transmitters using this system, 
whether for jamming or other purposes, might 
advantageously use the expendable sea-water 
primary battery recently developed. 

Amplitude-Modulation Methods 

As in the case of frequency modulation, 
various systems were developed for producing 
r-f signals amplitude-modulated by noise or 
other modulations more or less random in 
nature. Many of the circuits used were quite 
conventional, but a few of the less conventional 
methods employed are discussed below. 

Direct-Noise Amplification. A novel form of 
a carrier-suppressed (really carrierless) emis- 
sion is employed in the Dina type of trans- 
mitter. In its basic form this transmitter 
consists of a direct-noise amplifier (whence the 
name Dina) connected to a source of noise 
and designed to amplify in the r-f range in 
which transmissions are desired. Noise com- 
ponents at the desired frequency are thus 
amplified until they have sufficient power to 
be radiated. Consequently, there is no carrier 
and all the available output capacity of the 
transmitter is made available in sideband 
energy. This decreases by a considerable factor 
the output power required.^®^- 

In the design of Dina transmitters, diffi- 
culties arise from the necessity of tuning the 
wide-band amplifiers to choose the frequency 
band. Greater flexibility and overall simplicity 
may be achieved by generating the noise energy 
in a fixed frequency band and heterodyning to 
the desired transmission frequency. This 


GENERAL STUDIES OF COMMUNICATIONS COUNTERMEASURES 


171 


method has the added advantage that it makes 
possible the use of the output of the noise source 
in the frequency range where it is most efficient. 
Another method is to generate noise between 
the limit of zero frequency and a higher limit, 
modulating thereby the output of an r-f oscil- 
lator, and then suppressing the carrier but 
amplifying the double sidebands to the level 
required. 

Noncoherent Pulses as a Noise Source. The 
idea of a noise source using short pulses with 
phase independent of the preceding pulse was 
taken up at an early stage of the work as 
having considerable promise. Its simplest form 
might consist of a self-quenched electronic 
oscillator in which the time between bursts of 
oscillation is long enough to permit the ampli- 
tude of the preceding pulse to die down below 
the background of thermal noise before the 
next pulse starts. The pulse which follows then 
grows from the thermal noise in the circuit, 
which provides the ''seed” necessary for the 
superregenerative growth of the oscillations, so 
that successive pulses possess randomness of 
phase. 

Theoretical considerations verify the experi- 
mental fact that, when used against a receiver 
having a narrow band, noncoherent pulses are 
substantially as effective for a given power as 
thermal-type noise. But for this to be true, 
the time between pulses must be small com- 
pared with the time constant of the receiver. 
As the time between pulses is decreased, one 
eventually finds that the oscillation no longer 
disappears in the background noise; the seed 
for a pulse is then not noise but the remains 
of the preceding pulse, and coherence of phase 
results. The shape of the spectrum is no longer 
smooth but consists of sharp peaks separated 
by an amount equal to the pulse-repetition 
rate; in the valleys between these peaks the 
victim station might escape. Hence wide-band 
receivers are favored if the pulse rate is too 
slow, whereas, if it is so fast as to cause 
coherence, narrow-band stations may be un- 
affected. 

Thus at the outset of a project in which 
noncoherent pulses are to be used one needs 
to know, among other things, the barrage 
bandwidth and the receiver bandwidth, for 


these are related to the pulse rate needed. The 
orders of magnitude are roughly indicated by 
the equation: 

= _L / 2 ) 

Pulse rate Barrage band Receiver band ^ ^ 

where a: is a function of the pulse length and 
randomness in phase and is determined by an 
examination of the output spectrum, which 
has a sin x/x shape. The value of x is not 
affected by the pulse-repetition frequency 
[prf ] . The minimum pulse rate is thus implicit 
in the barrage and receiver bands. To meet 
in addition the requirement of noncoherence 
requires that in the decay period the residual 
oscillation must attenuate from full pulse power 
to something that is lost in the background 
noise.i^^ 

Spark Sets as Jammers. In the survey of 
diverse types of apparatus which might be used 
for causing interference, it is not surprising 
that a besetting sin of the earliest means of 
radio communication — ^the spark — was seized 
upon as a possible virtue for RCM purposes. 
The spark offers a natural tendency toward 
wide bands, to the extent that much of the 
difficulty of the earlier radio development arose 
in obtaining low decrement or narrow bands. 
The circuits concerned are relatively simple, 
and large powers had already been achieved, of 
course, in the old days of the spark. It was 
apparent, however, that much effort would be 
needed to develop a spark gap suitable to the 
high frequencies of greatest interest and 
capable of producing the large number of 
sparks which are needed, both to give the wide 
bands required and to nullify the AJ effects 
of limiting. 

A theoretical study^^^ of the spark when used 
for these purposes showed that the spectrum 
produced is related in a simple manner to the 
transfer admittance of the filter making up 
the discharge circuit, and that acceptable 
efficiencies might be expected, at least at the 
lower frequencies. These theoretical conclu- 
sions were encouraging. 

A laboratory study^^^ was made, therefore, 
to determine the interference value of sparks 
for barrage work.^^^^* ^is appears that sparks 
are feasible for jamming and are better suited 


172 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


to barrage than to spot jamming. The r-f noise 
power which can be expected with the tech- 
niques considered is of the order of 50 w in 
the German tank band (near 30 me), but for 
frequencies which are significantly higher 
sparks have little promise. Their most natural 
range would be below 5 me, where wide bands 
and powers of many kilowatts seem reasonable. 
Unfortunately, this is not the frequency range 
where high-power barrages are likely to be 
desired. The special case of the expendable 
jammer is an exception.^^^- 

Generally speaking, the considerable special 
development work of an electrical and mechani- 
cal nature which would be required for most 
projects and the high state of development of 
electronic equipment tended to discourage the 
thought that sparks have a special advantage. 
It is, however, a means which should not be 
completely overlooked. 

Expendable Jammers 

The use of parachute-borne, expendable 
jammers that can be dropped in the immediate 
vicinity of the receivers to be jammed offers 
interesting possibilities. Expendable jammers 
may be of several types, such as parachute- 
borne (to jam during the period of descent), 
grounded (to jam from the ground), and float- 
ing (to screen small boats, etc.). In general, 
jammers of this type will not be effective 
against systems having highly directive an- 
tennas unless the jammers are directly in the 
beams of the antennas. Thus, in the case of 
radar, expendable jammers are of doubtful 
value because of the difficulty, if not impossi- 
bility, of keeping them in the radar beam. In 
the communications field, on the other hand, 
expendable jammers have possibilities, since 
highly directional antennas are seldom used for 
the services under consideration. Here, as in 
all other cases where the merits of various 
types of jammers to accomplish a given end are 
being weighed, consideration must be given to 
the weight, bulk, life, and effectiveness of the 
various devices that are available. 

During the summer of 1943, the development 
of expendable jammers (Chicks) was under- 
taken along lines related to work already well 
under way at Signal Corps and Canadian 


Service laboratories. Duplication was avoided, 
but the possibilities of the general method 
whereby large numbers of small expendable 
jammers would be sown near enemy receivers 
were considered of great importance, as was 
expressed by representatives of the Armed 
Services at liaison meetings. 

Ideas as to a number of devices were current, 
all of which had in common the possibility that 
they would be used but once and that by some 
means they would be planted near enough to 
important radio receiving points of the enemy 
to disrupt reception in spite of the fact that 
the power could not be great. This would, in 
general, permit our own use of the same fre- 
quency range, because only a very limited 
geographical area would be affected. Various 
methods of planting were considered, including 
shooting in shells and free fall or parachute 
drop from aircraft. Work was actually under- 
taken to develop apparatus in which parachutes 
would soften the fall and in which the antenna 
would be designed for dropping in jungles. The 
frequencies from 1 to 7 me were to be covered 
by the first models.^®^* 

Conversion of Communication 
Transmitters into Jammers 

It is often possible, with relatively little 
effort, to convert an existing radiotelephone 
transmitter into a jammer by the simple ex- 
pedient of providing suitable modulation. This 
expedient may prove to be a quick method of 
obtaining jammers where standard equipment 
is available that has sufficient output power to 
be effective and covers all or even a part of 
an enemy communications band. 

There are two simple methods of obtaining 
a satisfactory signal for modulating the trans- 
mitter. One is to place the regular microphone 
in a noisy location, such as an engine nacelle 
(the British call this Tinsel). A second method 
is to make use of receiver noise by connecting 
the output of a convenient receiver to the micro- 
phone input terminals on the transmitter and 
adjusting the modulation controls for a maxi- 
mum amount of sideband energy. This type of 
improvisation results in a spot jammer, since 
the width of the sidebands in a transmitter of 
this type is generally limited. Under these 


COMMUNICATIONS JAMMERS AND ASSOCIATED EQUIPMENT 


173 


circumstances it is essential that the trans- 
mitter carrier be set as close as possible to 
that of the victim. 

Studies of Specific Jamming Systems 

It is sometimes practical to use automatic 
devices that seek the victim signal, accurately 
align the jammer to its frequency, and then 
periodically monitor the enemy transmissions 
in order to terminate the jamming as soon as 
the enemy no longer uses the channel that is 
being jammed. Because of the feature of listen- 
ing through one’s own jamming, these devices 
are sometimes called listening-through systems. 

It should be borne in mind that there is a 
simple counter-countermeasure for any listen- 
ing-through device that stops jamming and 
moves on to the next signal as soon as the 
victim signal disappears. The victim station 
would only have to interrupt his transmissions 
long enough for the jammer to note its absence 
and to cease jamming. It would then be possible 
to make use of the equipment that had been 
jammed, at least until the jammer again re- 
turned to its frequency. From the point of view 
of the jammers, difficulty on this score can be 
obviated by jamming any signal for a pre- 
determined period of time without listening 
through. 

The development of the most effective jam- 
ming system to meet a given set of circum- 
stances requires a knowledge of the characteris- 
tics of our own and enemy communication 
equipment in the frequency range of interest, 
the type of antennas and polarization used by 
the enemy, the type of terrain involved, and 
radio-propagation characteristics. Although 
the detailed steps in a given study will depend 
on the type of enemy radio link to be jammed, 
the frequencies involved, the tactical situation, 
the availability of jamming equipment, etc., 
each specific problem should be approached 
from a systems viewpoint, in order that proper 
allowance be made for all factors involved and 
the best jamming equipment selected for the 
job. 

This procedure is described elsewhere.^^^ Its 
application to a few specific problems is well 
illustrated in the several studies mentioned 
below. Although the solutions given in these 


reports apply to the specific conditions im- 
posed, much of the material is of general use. 
Naturally, the development of better equipment 
as time goes on will result in a different 
solution to the same type of problem, but the 
reports illustrate a method of attack which 
should be useful to others confronted with 
similar problems in the future. 

One of these reports-^^ deals with an airborne 
spot-jamming system study, made at the re- 
quest of the Air Communications Officer, which 
led to recommendations for a system to jam 
German day-fighter communications, in an 
effort to block coordinated attacks by enemy 
fighter groups on our bomber formations. 

Another of these reports-^^ deals with studies 
relating to an airborne bar rage- jamming sys- 
tem for use in jamming: (1) ground-to-ground 
communications (as exemplified by the German 
tank circuits operating in the 27.2- to 33.4-mc 
band) , with the jamming to be carried out by a 
limited number of specially equipped planes; 
and (2) ground-to-air communications, as 
exemplified by the German ground-controlled- 
interception [GCI] system operating in the 
38.4- to 42.3-mc band, where the jamming 
was to be carried out by equipment carried in 
planes on bombing missions. 

An earlier study was made of spot jamming, 
as applied by equipment in bombers, against 
German ground-to-air communications.^^® An- 
other study of a different sort relates to the 
use of expendable jammers of the spark type 
dropped from planes to jam radio communica- 
tion in a given area.“®® 


COMMUNICATIONS JAMMERS AND 
ASSOCIATED EQUIPMENT 

In this section, the various communications 
jammers and jamming systems developed 
under Division 15 are described briefly, to- 
gether with associated devices such as ampli- 
fiers. More detailed descriptions of the 
equipments can be found in the various reports 
given as references for each piece of apparatus 
discussed, and a history of the development 
can be obtained, if desired, from the series of 
Division 15 progress reports. 


174 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


8.3.1 Barrage Jammers and Amplifiers 

It should be noted here that the 1-f Dina 
transmitter, which with its associated receiver 
(Dinamate) forms the AN/ARQ-8 jamming 
system, was developed originally as a communi- 
cations barrage jammer. Its chief applica- 
tions, however, were as a countermeasure to 
guided missiles and the Japanese 80-mc gun- 
laying [GL] radar; it is therefore discussed in 
Section 8.4 and in Chapter 11 rather than here. 
A lightweight transmitter of the Dina type was 
also developed but was never put into produc- 
tion. 

Noncoherent Pulse Jammer 
AN/ ART-2 (Pad) 

The AN/ART-2 transmitter was developed 
in response to a Service request for a com- 
munications jammer to be flown in carrier- 
based fighter aircraft, primarily to jam 
‘‘walkie-talkies.’’ The requirements on the 
apparatus were finally established as follows: 
(1) The total weight of the installation was 
to be less than 40 lb. (2) The d-c power require- 
ment was to be less than 600 w. (3) The 
jammer had to be capable of being preset on 
the ground, so that the only attention required 
in the air was to turn it on. (4) The modulation 
was to be noise-type, with a bandwidth be- 
tween and % me. (5) The frequency range 
was to be from 21 to 50 me. (6) The antenna 
to be used was the existing 10-mc communica- 
tions antenna.^^^ 

Noncoherent pulses were chosen as the 
modulation which seemed most satisfactory, in 
general, against narrow-band receivers (where 
the jamming efficiency of this type of modula- 
tion is about equal to that of noise). In the 
form of modulation finally used in ART-2 
(Pad), the randomness between successive 
pulses was confined to their relative phase, for 
the shapes and instantaneous frequencies were 
repeated. But randomness in phase alone is 
sufficient to give a spectrum having roughly 
the sin x/x shape, with no characteristic asso- 
ciated with the prf. An artificially high back- 
ground noise was provided by means of shot 
noise from a phototube,^'^® and an amplifier 
following the oscillator was used for the sake 


of increased power and stability, and for assur- 
ing noncoherence (randomly phased pulses). 

The pulse rate used in Pad was 80 kc, and 
a barrage band of 400 kc was covered. If these 
figures are substituted in equation (2), one 
finds that the receiver bandwidth required to 
satisfy the equation is 32 kc. This figure means 
that Pad would be most effective against a 
receiver whose bandwidth is about this value; 
these data were not available during the de- 
velopment of the jammer. Later tests showed 
that the Japanese walkie-talkie receivers had 
broad-band characteristics which required an 
increase in the pulse rate and duty cycle of Pad. 

At about this point the decision had to be 
made between the self-quenched and the sepa- 
rately quenched oscillator. Pad used self- 
quenching. The principles of the self-quenched 
type of oscillator are set forth in a report^^^ 
which also goes into the details of the circuit 
design of Pad.^®^ Effectiveness tests^^^ and 
flight tests of the ART-2 showed that it met 
satisfactorily the requirement that it jam a 
Japanese walkie-talkie link 0.4 mile long from 
a distance of 25 miles at 14,000 ft in altitude. 
It was realized, however, that the pulser is 
actually inferior to resistance noise. On theo- 
retical grounds, it was believed that two or 
more Pads would have a far greater jamming 
efficiency than a single one, an idea which was 
borne out by laboratory and Navy flight tests. 
Consequently, when Pads were staggered every 
quarter megacycle, in accordance with the 
original Navy plan, the overlapping of the 
spectra gave enough improvement that the 
resulting signal was not much inferior to 
random noise in jamming efficiency.^®^ 

Expendable Jammer (Chick) 

Reference has already been made (Section 
8.2.5) to the idea of using expendable jammers 
against communications networks. The Na- 
tional Defense Research Committee [NDRC] 
work on this project took the form of providing 
a Chick in which the interference was pro- 
duced electronically, instead of by a spark, as 
was the case with the original models.^^^ A 
number of different shapes for the jammers 
were considered. Greatest attention was given 
to the bomb-shaped Chick,^®® but designs were 


COMMUNICATIONS JAMMERS AND ASSOCIATED EQUIPMENT 


175 


drawn up and experiments made with radically 
different shapes.^^^ 

The problem of securing adequate radiation 
obviously was difficult. A Chick designed in 
Canada comprised a bomb-shaped device with 
fins, intended for dropping on cleared ground. 
A spring device was actuated when the nose 
struck the ground and the automobile-type 
antenna (drawn out by the supporting para- 
chute during launching) was swung perpen- 
dicular to the length of the container; at the 
same time, two lateral legs spread away from 
the case to form with it a three-legged support. 
The United States devices were for use in 
jungles where a long wire — say 100 ft long — 
would find support in trees. Neither of these an- 
tennas was likely to be dependably effective 
and could be very inefficient. 

A jamming analysis of Chick problems was 
made,^^^ and a study of the optimum size for 
such jammers was carried out.^^^ A final United 
States Chick model was developed and tested^**^ 
(including flight tests), and its performance 
analyzed.2^^ Tests were made also on the earlier 
United States and Canadian versions.^^^ Chicks 
were dropped successfully from airplanes going 
at speeds up to 300 mph, and in most cases 
were found to be in operating condition after 
landing on bare ground. Noise fields from 100 
to 200 pv per meter were produced at mile 
with the antenna directly on the ground. The 
jamming signal emitted was the equivalent of 
random noise; for the device was, in fact, a 
gas-tube noise source with several stages of 
r-f amplification. With this type of noise, ampli- 
tude limiters in the receiver do not constitute 
an AJ means as they do for simple spark-type 
jammers. The Chick bandwidth was such that 
10 or 12 units, each adjusted to a different 
frequency, would be required to cover the range 
of frequencies from 1 to 7 me. To jam teleg- 
raphy over this frequency range might require 
dropping a very large number of units. 

Converted Communications Transmitters 

Since there already existed a wide variety of 
ground and airborne radio communication 
transmitters when the RCM program was 
begun, steps were taken early in the program 
to adapt some of these for jamming purposes. 


As an example of this practical approach, one 
of the first procedures suggested for immediate 
application was that of increasing the gain of 
a spare receiver until sufficient thermal noise 
was obtained to modulate properly a communi- 
cation transmitter, whose radio frequency could 
then be adjusted to spot-jam any given enemy 
frequency in the operating band of the trans- 
mitter. Another source of noise modulation 
used in jamming was the output from a micro- 
phone placed in the engine nacelle of an air- 
craft. Later, a gas-tube noise generator (Gas- 
ton) was developed, and improvements were 
made on this early design. 

Studies were made of the modifications re- 
quired to convert standard communications 
transmitters for use as jammers with noise 
sources such as Gaston or other types of ex- 
ternal sources.®^ These modifications were car- 
ried out in the laboratory on the Navy GO-9 c-w 
transmitters^*^’ and on the i-f units from 
them;2i® and prototypes were furnished the 
Armed Services. Similarly, modifications of the 
SCR-808 set were made to provide a stopgap 
airborne spot jammer which could be used 
against German tank and parachute troop fre- 
quencies,^^^ and later an SCR-828 was modified 
and given flight tests.^-^ 

The 15-kw Ground Jammer (Cigar) 

The 15-kw ground Cigar was a high-power 
ground jammer originally intended for jam- 
ming the German ground-to-air communica- 
tions link used in controlling night-fighters. It 
consisted of a Lecher-line oscillator using two 
triode tubes (Type 889R) cooled by forced 
air.*oo, 301 frequency was mechanically swept 
through a range of about 4 me around a mean 
frequency which is adjustable between 30 and 
50 me. 

Various modifications were made in this 
equipment. A filter was designed to suppress 
harmonics of the radio frequency, to avoid 
interference to friendly communications chan- 
nels in the 100- to 150-mc range.^*^ ^ different 
type of audio modulation was developed to 
make existing Cigars useful in a related appli- 
cation; modification kits were manufactured 
and installed in the dozen or so units in serv- 
ice.^** 


176 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


Another modification desired was to convert 
the Cigar to a more efficient type of oscillation, 
preferably a random type of noise. Two meth- 
ods of operation partially meeting the request 
were developed.^®^ The first of these used non- 
coherent pulses which were self-quenched, as 
in Pad, and gave a power of 2 to 3 kw over an 

0.7-mc band, at 40-mc mid-band. The second 
method was a separately quenched system of 
grid modulation, driven by the amplified video- 
frequency output of a gas tube; it gave 12 kw 
over an 0.5-mc band at 40 me. This power was 
considerable, and the bandwidth was one of 
interest. The full capabilities were not realized, 
since this particular job was discontinued be- 
fore completion on account of the general war 
situation. 

In the course of this latter development, a 
number of experiments were made on separate 
quenching which give some information on 
the peculiar impedance that an oscillator pre- 
sents to the triggering input circuit. These 
peculiarities arise from the fact that in a power 
oscillator the triggering terminal in general 
carries considerable current — for example, grid 
current. As the bias voltage becomes less nega- 
tive and passes the point where oscillations 
start, a discontinuity occurs, and another ap- 
pears at the stopping of oscillation. The input 
conditions are thus nonlinear in nature and 
require considerable driving power. The neces- 
sary decay of oscillation can be helped by using 
a gated-damper tube, which operates during 
the silent interval like a damper in a piano. 
Alternately, the amount of background noise 
can be raised by using a noise amplifier between 
the noise source and the oscillator, as was done 
in an English jammer. 

Power Amplifier for Jammers 

The AM-66/AR-XR was developed as an air- 
borne power amplifier for jammers in the 14- 
to 55-mc range. As a preliminary to the devel- 
opment work, a considerable amount of general 
research was carried out on the best design for 
such an amplifier.^®^ The AM-66 was designed 
to step up the output of such jammers as the 
AN/ARQ-1 and the AN/ARQ-8 (5 to 25 w) to 
about 500 w. This mid-band power was achieved 
for all frequency settings within the range with 


a half-power bandwidth of 2 me. Several proto- 
type equipments were built, and full laboratory 
and flight tests were performed, as well as 
tests of ruggedness.2^^ 


® Spot Jammers and Jamming 

Systems 

The following spot jammers and spot-jam- 
ming systems were developed in Division 15. 

Spot Jammer for 15 to 30 mc 

A research program was initiated to develop 
a spot- jamming system covering the frequen- 
cies between 15 and 30 mc. The final develop- 
ment model was used as a prototype for the 
Army SCR-591 and the Navy AN/ARQ-10 
jammers. 

Development Program. The development pro- 
gram undertaken was based on four general 
requirements for a spot- jamming system: (1) 
means for interception and identification of an 
enemy signal, (2) means for supervision of the 
enemy transmission, (3) means for setting the 
transmitter, and (4) means for modulating 
the carrier to give the most effective signal. 
The development, therefore, took shape as 
follows : 

1. The equipment was to include a receiving 
system capable of spotting and recognizing the 
transmission of the enemy anywhere within 
a band and of measuring the frequency of the 
transmission intercepted. This was accom- 
plished by a scanning receiver, which used a 
rotating condenser in parallel with the main 
tuning condenser. The frequency band covered 
by the scanning process was roughly 5 per cent 
either side of the mid-frequency. The frequency 
band covered by the equipment itself extended 
from 15 to 30 mc in three sub-bands. 

2. Means had to be provided for observing 
the enemy’s transmission during jamming in 
order to know whether the jamming was on 
frequency and to follow as quickly as possible 
any frequency change of the enemy’s trans- 
mission. For this purpose, the jamming trans- 
mitter was interrupted at a rate of ten times 
per second in synchronism with the scanning 
operation in the receiver. Half of the time, the 


COMMUNICATIONS JAMMERS AND ASSOCIATED EQUIPMENT 


177 


transmitter was on, half of the time off. During 
the off periods, the enemy signal could be ob- 
served on the screen of a cathode-ray tube. 

3. Setting the jamming transmitter rapidly 
and accurately to the same frequency as the 
enemy transmission, as seen on the receiving 
oscillograph, is most important, so that jam- 
ming can be started quickly and efficient use of 
the jamming power insured. This result was 
achieved by using a transmitter which was 
simply a self-excited oscillator, the main tuning 
of the transmitter being ganged with the re- 
ceiver tuning. Additional trimmer tuning of the 
transmitter allowed accurate frequency setting. 
During the first part of the development, it was 
discovered that the method of superimposing 
the transmitter signal and the signal received 
from the enemy as seen on the cathode-ray tube 
did not give sufficient accuracy of tuning. In 
order to improve this condition, a special tuning 
position was provided during which scanning 
was removed and the cathode-ray tube used in 
a manner similar to a peak voltmeter. This 
method in itself was not entirely satisfactory; 
in further developments for the Navy it was 
discarded in favor of a very accurate counting 
method. 

4. The carrier had to be modulated in such a 
manner as to render the jamming most effec- 
tive, i.e., to realize the best possible masking 
effect for a given power (see Section 8.2.2 and 
Chapter 9). In this development simple means 
were used, the most successful one being a saw- 
tooth modulation of variable pitch. The audio 
frequency was continuously changed at random 
within a range of ±800 c around an average 
frequency of approximately 1,000 c. Further- 
more, in order to jam f-m communications effi- 
ciently, a mechanical frequency wobbler was 
provided. 

Results Obtained. The equipment built was 
a laboratory modeU^* of an airborne jam- 
mer, which was tested in July 1942 during 
maneuvers in Louisiana. The tests were extraor- 
dinarily successful, with one single jammer 
disrupting the communications of an entire 
division. These test results were largely respon- 
sible for the great effort in communications 
countermeasures which was started thereafter. 
The Army requested 50 sets identical to the 


prototype except for some variations in fre- 
quency band; the revised model was known as 
the SCR-591. These sets were built and deliv- 
ered, after a relatively long delay due to the 
necessity of redesigning for production. 

The experience gained during this develop- 
ment can be summarized as follows. (1) By 
far the most important question for efficient 
jamming is accurate tuning on the enemy fre- 
quency. (2) If look-through features and iden- 
tification and control of the enemy are desired, 
a spot-frequency jammer is a complex piece of 
equipment. (3) The difficulty of visualizing the 
exact tactical use of such equipments necessi- 
tates a very broad frequency coverage, which 
in turn still further complicates the equipment. 
(4) If provision for jamming telegraphy is 
required, the accuracy in frequency tuning has 
to be extreme (within a few cycles per second) . 
These conclusions were embodied in the Navy 
equipment AN/ARQ-10, which was developed 
on the basis of the laboratory model described 
above. A 500-w airborne amplifier for the 
ARQ-10 was designed also,^^^ the AN/ARA-13, 
which covered from 1.3 to 42 me in two steps : 
the AM-80/ARA-13 went from 1.3 to 11 me, 
and the AM-96/ARA-13 from 11 to 42 me. 

Listening-Through Systems 

A study was made of problems of listening 
through radio jamming. The technique gained 
during earlier work was expanded and used in 
the development of broad-band (18 to 80 me) 
and narrow-band (±15 to 100 kc) scanners for 
use with radio receivers covering the frequency 
range 1.8 to 80 me. These scanners and receiv- 
ers were used in radio sets AN/ARQ-9 and 
SCR-596-T-2, which were spot jammers devel- 
oped under direct Army contracts. 

An important part of the work was consulta- 
tion and advice on numerous other NDRC and 
Service projects involving r-f scanning in con- 
nection with either searching for or jamming 
communications signals. 

Summary. Two general types of radio re- 
ceivers were required for spot jamming. A 
broad-band scanning receiver was used in lo- 
cating enemy signals and observing their fre- 
quency shifts during evasive tactics. A narrow- 
band receiver combining aural and visual 


178 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


indication was used to identify signals and to 
align jamming and victim frequencies. Syn- 
chronous control of the jamming transmitter 
and both types of receivers was necessary in 
order that the receivers might listen through 
during brief pauses in the jamming signal. 

The broad-band scanning technique developed 
was used when broad r-f bands were to be 
scanned during intervals too short for the vic- 
tim to pass effective intelligence, such as 1/30 
sec. This work led to the 18- to 80-mc scanner 
in AN/ARQ-9, but the principles are also ap- 
plicable to other frequency ranges. The devel- 
opment problems were more severe than those 
of communication receivers because of the wide 
range of input levels encountered and because 
normal AVC and r-f preselection was not feasi- 
ble.“^® Among the problems for which typical 
solutions were found were the questions of 
design objectives and the choice of receiving 
circuits, the choice of local oscillator and inter- 
mediate frequencies to minimize spurious re- 
sponses, and the synchronization of a mechan- 
ical-scanning oscillator with an electronic 
jam-scan cycle and narrow-band scan. 

The narrow-band receiver technique involved 
aural receptions with a narrow-band scanner 
connected to the i-f amplifier to afford visual 
observation of radio signals at frequencies near 
the one to which the receiver is tuned. Special 
consideration was required not only for the 
scanning circuits but also for the r-f and i-f 
circuits common to both aural and visual re- 
ception. The problems considered^^® included 
the following : the choice of oscillator and inter- 
mediate frequencies and their effects on spuri- 
ous aural or visual responses; desirable gain 
distribution and overload capacities throughout 
the receiver; the achievement of a gang-tuned 
r-f band-pass input selectivity, adequate for the 
scanning bandwidth, with regard to the usual 
tuned circuit selectivity ; and the limitations of 
typical circuits. 

A preliminary design for an airborne multi- 
ple spot- jamming system was developed.^^^ In 
this system up to four AN/ARQ-9 radio trans- 
mitters could be operated simultaneously in the 
same airplane in order to jam an equal number 
of communication channels. Both narrow- and 
broad-band monitoring facilities were included. 


Synchronous control of all transmitters and of 
the frequency scanners was provided as an aid 
to the observation of victim signals. An oper- 
ations plan for this system was worked out.^^s 

Further Work. Many problems in connection 
with listening through and associated narrow- 
and wide-band scanning receivers remain to be 
solved before the relative merits of different 
types of systems can be evaluated with ease or 
their performance predicted for all frequency 
bands. The importance of obtaining general 
solutions is contingent on operational require- 
ments and may depend in part on common 
interest with other uses such as communications 
searching and monitoring. Careful study and 
reporting of the performance of equipment 
designed for specific uses and of effects when 
used under abnormally severe conditions would 
do much to indicate which problems are most 
pressing. 

Some of these problems are listed here with- 
out any attempt to evaluate their relative im- 
portance: (1) Comparison of the merits of 
broad-band scanners having synchronously 
swept r-f selection with those having broad- 
band r-f selectivity where only the heterodyne 
oscillator frequency is shifted at the scanning 
rate. (2) Study of frequency converters and 
methods of coupling to heterodyne oscillators, 
without excessive noise penalty and with a 
minimum number of spurious responses in cov- 
ering wide frequency ranges and signal-level 
differences. (3) Improved synchronization of 
electronic and mechanical scanning. (4) Im- 
provement of mechanically swept oscillators by 
reducing the retrace time. (5) Electronic con- 
trol of f-m oscillators for use at higher fre- 
quencies with larger percentage swings. (6) 
Means for preventing a jammer in one airplane 
from interfering with a broad-band scanner in 
an adjacent airplane which is operating in the 
same frequency band. (7) Means for reducing 
radar interference in scanning receivers. (8) 
Use of balanced r-f circuits, to reduce re-radi- 
ation and spurious responses at harmonics of 
signal frequencies. 

Jammer Alignment Systems 

Various means have been proposed for auto- 
matically aligning a jammer with a victim 


GUIDED MISSILES JAMMERS AND ASSOCIATED EQUIPMENT 


179 


signal.®® A theoretical study was made to com- 
pare some of these methods it was limited 
to electronic rather than mechanical tuning. A 
few of the mechanical methods are described 
above, in the discussions of the jamming sys- 
tems into which they were incorporated. 

Single Quado. The first approach to the prob- 
lem was the development of a small visual indi- 
cator to be used with a radio receiver for the 
comparison of two carrier frequencies differing 
by less than 5 c, even though one or both of 
the carriers are keyed on and off at hand- 
telegraph speeds. The first unit developed, 
known as the Single Quado, contained a small 
motor-driven rotary neon Strobotron and a 
thyratron tube keyer stage.®® With a steady 
received carrier the audio beat note of the 
receiver flashed the neon at the beat rate, and 
the flashes could be made to appear stationary 
by adjusting the frequency of the receiver beat 
oscillator. When the received carrier was keyed 
on and off, the flashes always appeared and 
disappeared in the same angular position on 
the Strobotron. The comparison with another 
carrier was made by switching the receiver to 
the new signal ; and the speed of the neon motor 
provided the memory function. 

Tests by the Navy indicated that the Single 
Quado instrument was not suitable for use in 
aircraft, primarily because of its susceptibility 
to noise and the frequency instability of the 
receiver beat-note output. 

Dual Quado. Another development was the 
Dual Quado, similar to the Single Quado but 
with some circuit improvements.^^^ Two rotary 
neons with a switching arrangement connected 
the beat note of two carrier frequencies to their 
respective Strobotrons. The Dual Quado was 
satisfactory for noiseless signals, but it was 
unsuitable for the application intended on ac- 
count of the difficulty in adjusting the beat note 
under conditions of noise and random keying 
of one or both of the signals. 

Stopwatch. A different approach to this prob- 
lem was an automatic device known as Stop- 
watch for holding the jammer signal within a 
few cycles per second of the victim signal.®®’ 
Stopwatch was developed particularly for jam- 
ming telegraph signals operating in the fre- 
quency range from 1 to 20 me. A demonstration 


model was designed for the frequency range 
from 2 to 5 me which incorporated the essential 
components of a radio receiver, transmitter, 
and exciter, and a servomechanism. By means 
of a common heterodyne oscillator, it was pos- 
sible automatically to maintain the frequency 
of the transmitter exciter to within 10 c of 
the received carrier frequency, when this car- 
rier was keyed at hand-telegraph speeds. Com- 
plete jamming was obtained with a J/S voltage 
ratio of unity. Compared with existing jam- 
mers using random noise or some similar mod- 
ulation, this jammer represents a saving in 
power of approximately 100 to 1. 

On the basis of the experimental equipment, 
a preproduction model covering the desired 
frequency range was designed®®® and a small 
number manufactured, both commercially and 
by the Signal Corps. Since this set proved satis- 
factory, regular production was initiated. 

Recommendations for Future Work. Prob- 
ably the most effective AJ device known is c-w 
telegraphy. Good operators can copy intelli- 
gence through certain types of noise or jam- 
ming 20 db stronger than the signal; and to 
do an efficient job of jamming telegraphy, it is 
necessary to place the jammer within a few 
cycles per second of the victim signal. This is 
the unique purpose of Stopwatch, which dis- 
tinguishes it from jammers using similar prin- 
ciples. It is believed worth while to develop the 
Stopwatch principle further and to develop 
equipment of various frequency ranges and 
powers for ground and airborne use as indi- 
cated by tactical problems. 


GUIDED MISSILES JAMMERS AND 
ASSOCIATED EQUIPMENT 

This section lists and describes the jammers 
and jamming systems developed in Division 15 
for use against guided missiles. The distinction 
between communications and GM jammers is 
not always quite definite, since their frequency 
ranges are about the same, and many trans- 
mitters can be used for either purpose ; indeed, 
some jammers, such as Dina, have been used 
against 1-f radars also. 


180 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


Ground-Based and Airborne 
Jammers and Systems 

Transmitters intended specifically to jam the 
control systems of enemy guided missiles could 
not be designed or built until information was 
available on the frequencies and control meth- 
ods used. The first GM jammers, therefore, 
were communications jamming systems used 
for this purpose, or other transmitters hastily 
converted into jammers. The background of 
techniques and knowledge gained through the 
development of communications countermeas- 
ures, however, made it possible to design GM 
jamming transmitters in a surprisingly short 
time. 

High-Power Ground-Based Jammer 
AN/GRQ-1 

In July 1944, the Signal Corps requested four 
high-powered jamming transmitters for coun- 
termeasures use against radio-controlled GM. 
Specifications for the jammers were based upon 
intelligence reports, which were enlarged upon 
through reasonable engineering estimates and 
consideration of previous GM experience. These 
specifications required operation over a carrier- 
frequency range from 20 to 60 me, with pro- 
vision for rapid frequency adjustment over a 
10-mc band while the equipment was in oper- 
ation. The power output was to be at least 50 
kw, and the output signal was to be 100 per 
cent amplitude-modulated by a square wave, 
with a 50 per cent duty cycle and a pulse-repe- 
tition rate between 100 and 15,000 c. 

Modifications to Commercial Equipment. 
Since these jamming equipments were urgently 
needed, it was decided to modify existing 50-kw 
power amplifiers rather than to attempt a com- 
pletely new design. A thorough survey of avail- 
able equipments showed that three suitable 
commercial amplifiers with power supplies, 
built for use in f-m broadcasting transmitters, 
could be procured. These were ordered, and 
modification work was initiated immediately 
upon receipt of the first equipment. In addition, 
preliminary work was begun on the construc- 
tion of a fourth equipment from available 
components. 

The modified transmitting equipment, identi- 


fied as the AN/GRQ-1, consisted of a variable- 
frequency, self-excited oscillator, utilizing a 
pair of Type 8009 vacuum tubes tuned by sec- 
tions of transmission line ; a keying modulator, 
providing the required square-wave modula- 
tion; a three-phase bridge-type rectifier, using 
six Type 869B mercury- vapor rectifier tubes; 
a power and interlock control panel; and a 
water-cooling system.^-^ input requirement 
of the equipment was approximately 125 kw 
of three-phase, 60-c power at 220 v, and the 
normal r-f output power was 50 kw with a plate 
efficiency of approximately 60 per cent. 

The modification of the 50-kw amplifier in- 
volved its conversion into a push-pull (double 
Hartley) power oscillator using a plate trans- 
mission line as the frequency-determining ele- 
ment, with feedback capacitors from the plate 
of each tube to the grid of the opposite one. 
The adjustable plate line originally provided 
in the amplifier was extended, and additional 
shorting sliders and actuating mechanisms 
were provided to permit tuning over the re- 
quired frequency range. The rectifier power 
supply which provided the high-voltage direct 
current for the power-amplifier stage of the 
original equipment was used without modifica- 
tion to supply plate power for the oscillator. A 
modulation system was designed and con- 
structed to give the required waveform ; it was 
composed of an electronic keyer, whose keying 
frequency was determined by a sinusoidal input 
signal from a conventional audio oscillator. 

Concurrently with the modification of the 
power amplifier, h-f and 1-f antennas for use 
with the jammer were designed. To provide 
for all required radiation patterns, the com- 
plete antenna system included four vertically 
polarized half-rhombic antennas and four hori- 
zontal rhombics. A system of transmission 
lines and switching circuits for both balanced 
and unbalanced operation linked the transmit- 
ter to the antenna system. 

The modified transmitter was tested with a 
balanced dissipative transmission line load. 
After final tests were completed, the first unit 
was packed for shipment to the United King- 
dom on August 27, 1944, and modification of 
the remaining two equipments was begun. 

Installation. Before this shipment arrived. 


GUIDED MISSILES JAMMERS AND ASSOCIATED EQUIPMENT 


181 


changes in the requirements of the Armed 
Services made unnecessary the use of the 
AN/GRQ-1 jamming equipment at a fixed site. 
It was decided that the engineers who had 
gone to England to aid in the installation of 
the jammer should undertake further modifi- 
cation, to render the transmitter mobile and to 
fit it for use as a general-purpose jammer in 
addition to its original function. The modifica- 
tion work was completed with actual radiation 
tests by December 8, 1944. In this mobile in- 
stallation the entire AN/GRQ-1 equipment, 
including a single vertical half-rhombic antenna 
and a spare, was accommodated in five trucks 
for ready transport. 

As a result of the above-mentioned changes 
in Service needs, the number of jamming equip- 
ments to be produced was decreased to three. 
Work on the fourth equipment was therefore 
stopped; but the modification of the two re- 
maining equipments was completed, and the 
equipments were delivered to the Signal Corps. 

The mobile installation involved many 
changes, generally of a minor nature, in the 
AN/GRQ-1 equipment. Mountings for many of 
the component parts of the equipment were 
strengthened or otherwise modified; and cir- 
cuit changes to increase ease of operation and 
maintenance were effected. In addition to such 
modifications, designs were produced for a 
frequency-sweeping modulator arranged to 
swing the frequency of the main oscillator dz3 
me at a rate of approximately 100 c. Considera- 
tion was also given to the problem of using a 
search receiver in the immediate proximity of 
the AN/GRQ-1 equipment while the latter was 
in operation ; and a “look-through’^ system was 
proposed as a possible solution. 

Automatic Search Jammer (Broom) 

Basically, the Broom-type automatic search 
jammer^-^ originally intended for use against 
guided missiles such as the HS-293 comprised 
a radio receiver and a transmitter utilizing 
common LC circuits, whose resonant frequen- 
cies could be adjusted by a variable tuning 
capacitor. The common tuning capacitor was 
motor-driven, and as it rotated in one direction 
the capacitance of the tuned circuit was varied 
from a minimum to a maximum and thence to 


a minimum as the fixed and movable plates 
moved into and out of coincidence. Accord- 
ingly, the operating frequency of the receiver 
and the transmitter was swept back and forth 
through the chosen search band, 45 to 51 me. 
The output of the receiver was amplified and 
applied to a trigger circuit which, when tripped 
by the reception of the signal in the search 
band, turned off the receiver and turned on the 
transmitter. At the same time, the drive motor 
was reversed. The timing circuit associated 
with the trigger circuit restricted the reverse 
operation of the motor and, after a chosen short 
interval, again reversed the motor and returned 
the transmitter and receiver to the initial 
search condition. 

The time constant of the timing circuit was 
so chosen that in the presence of a continuing 
signal in the search band the tuning capacitor 
was turned back and forth, tuning the equip- 
ment through a narrow frequency band cen- 
tered on the carrier frequency of the enemy 
transmission. The drive motor was reversed 
and caused to run backwards for a short period 
each time the receiver was tuned through the 
enemy signal. This operation continued as long 
as the enemy transmission was present. As 
soon as it was terminated, the motor was again 
allowed to run continuously in a single direc- 
tion, re-establishing the condition for search 
operation. 

Several experimental jammers were con- 
structed utilizing these basic principles. In the 
most highly developed one, a superheterodyne 
receiver was used, and the transmitter and 
receiver utilized the same doublet antenna. The 
transmitting oscillator and the r-f stage of the 
receiver used a common LC tank circuit, 
the resonant frequency of which was adjusted 
by means of a pair of variable capacitors. These 
capacitors were ganged together with those in 
the local oscillator and mixer stages of the re- 
ceiver and driven through reduction gearing 
by a two-phase motor, which was controlled by 
the receiver through a peak-firing trigger cir- 
cuit. A vernier drive was used for the tuning 
capacitors, to reduce the width of the jamming 
band with respect to that of the search band. 
For this purpose, the single set of ganged tun- 
ing capacitors was driven through a standard 


182 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


bandspread tuning drive with a speed reduction 
of 5 to 1. 

Tests on the completed equipment indicated 
that a jamming bandwidth of 100 kc could be 
obtained at the center of a search band extend- 
ing from 45 to 52 me with proportionately 
broader or narrower jamming bands at the 
limits of the search band. It was concluded that 
the Broom-type jamming system could be used 
successfully and with good efficiency for the 
jamming of a single enemy transmission oc- 
curring within a chosen search band ; if two or 
more enemy signals, however, should occur 
simultaneously in the search band, only one of 
them could be jammed with a single Broom. 
Furthermore, additional Brooms could not be 
operated in the same search band for jamming 
a second or third enemy signal, because one 
Broom would then jam another unless all were 
carefully interlocked. In view of these conclu- 
sions, further development work on the Broom- 
type jammer was abandoned in favor of other 
approaches to the general problem. 

Automatic Search Jammer (Beagle) 

An experimental model of this type of auto- 
matic search jammer^-^ (also intended for use 
against guided missiles) was developed. It was 
a single-frequency jamming transmitter which 
automatically tuned itself to the frequency of 
the victim signal, in the range 46 to 51 me. It 
consisted basically of a receiver, a control unit, 
a modulated transmitter, and two servo sys- 
tems. 

The receiver servomotor drove the ganged 
tuning capacitors in the receiver (and also a 
rough tuning capacitor in the transmitter) to 
sweep the desired band. When a signal was 
encountered, the receiver output actuated the 
control unit, which caused the receiver servo- 
motor to tune the receiver to the frequency of 
the incoming signal; a mechanical brake was 
then applied to the receiver servomotor shaft. 
An instant later, the jamming transmitter was 
turned on automatically, and the control unit 
caused the transmitter servomotor (which 
drove a vernier tuning capacitor) to tune the 
transmitter to the same frequency as the re- 
ceiver, thereby jamming the incoming signal. 
After a preset transmission time of 10 sec, the 


transmitter was turned off and the cycle of 
operation was repeated. 

In the final experimental model, the equip- 
ment was contained in two cases whose gross 
weight was approximately 45 lb. The receiver 
was adjusted to operate on signals from 100 to 
20,000 [IV in the band from 46 to 51 me. With 
these incoming signals, the frequency of the 
jamming signal always matched that of the in- 
coming signal to within 3 kc. The maximum 
length of time necessary to locate the enemy 
signal and then tune the transmitter to that fre- 
quency was 13 sec. The transmitter power out- 
put was about 38 w unmodulated and about 
50 w modulated with 1,000 c. No production 
models of this automatic search jammer were 
built. 

Signal-Repeating Jammer (Piano) 

To cope with the possibility that the type of 
modulation necessary to control well-designed 
guided missiles might be so complex as to pre- 
vent effective duplication for jamming pur- 
poses, another type of jammer was studied. 
Although this equipment was never developed 
to a working model, enough work was done to 
indicate the general feasibility of the ap- 
proach.^32 functional procedure proposed 
for the Piano is as follows. (1) Listen over the 
entire monitored band for an interval of time, 
memorizing the carrier frequency of all signals 
received. (2) Memorize simultaneously the fre- 
quency composition of the modulation on all 
signals. (3) Transmit on each of the memorized 
frequencies a carrier modulated with the proper 
memorized modulation. (4) Alternate the re- 
ceiving and transmitting intervals in such a 
fashion as to maximize the jamming and min- 
imize the tendency for the Piano to become a 
repeater. 

The “memory’" for carrier frequencies con- 
sisted of a bank of primary oscillators evenly 
spread across the monitored band. These oscil- 
lators were normally quiescent, but a particular 
oscillator would go into sustained oscillation 
when a signal appeared in its frequency band. 
A bank of such special oscillators was designed 
and built to work from the output of a broad- 
band amplifier. A more accurate memory could 
be attained by using a second bank of oscil- 


GUIDED MISSILES JAMMERS AND ASSOCIATED EQUIPMENT 


183 


lators with frequencies spaced up to half the 
difference between the frequencies of the pri- 
mary band, and by operating this second bank 
with the beat note between the received signal 
and the 'Triggered'' oscillator. With five banks 
of oscillators covering a 10-mc band at 50 me, 
it is ideally possible to reproduce a given fre- 
quency to within 10 c. Such a memory system 
would determine the frequency of all sidebands 
as well as that of the carrier, and consequently 
memorize the modulation as well as the carrier. 
This plan provided the basis for the first con- 
cept of the Piano. 

Since the beat note between the incoming 
signal and the first memory oscillator was the 
arithmetic difference between the two frequen- 
cies, it was necessary in reconstituting the sig- 
nal for transmission to use the sum and dif- 
ference of the primary oscillator frequency and 
the interpolation oscillation frequency. In prac- 
tice, it was necessary to transmit the primary 
oscillator frequency also, for this component 
could not be readily suppressed. 

Each added bank of interpolation oscillators 
therefore tripled the number of frequencies 
radiated. In the case of a five-bank Piano, the 
transmission of one signal would require the 
transmission of 80 other near-by frequencies, 
with the overall efficiency consequently low. 
The energy in the additional signals would not 
necessarily be completely wasted, however, 
since they would all be in the immediate vicinity 
of the desired one. 

A second version of the Piano called for 
only one bank of primary oscillators and one 
of interpolation oscillators. This system, of 
course, required the transmission of only two 
other near-by frequencies, with a consequent 
improvement in overall efficiency. In this ver- 
sion of the Piano the modulation was to be 
memorized by a group of oscillators in the 
1-f range which were subjected to the modula- 
tion envelope of the carrier. Ideally, a 
reasonable number of logarithmically spaced 
oscillators should be able to memorize the 
required modulation frequencies. Once the 
transmission frequencies were memorized, it 
would be a relatively simple matter suitably 
to mix, amplify, and transmit the output of 
the memory oscillator. 


Low-Power Airborne Jamming System 
AN/ARQ-8 

The AN/ARQ-8 jamming system consists of 
a transmitter (Dina) of the suppressed-carrier 
type and an associated receiver (Dinamate). 
The principles of this type of transmitter have 
been discussed to some extent previously (Sec- 
tion 8.2). Other carrierless Dina-type jammers 
were developed for special purposes in the 
communications frequency range,^®^’ but 
the ARQ-8 was the only one produced in 
any quantity. (The higher-frequency Dina, 
AN/APT-1, was used extensively as a radar 
jammer — see Chapter 11.) 

The ARQ-8 was developed originally for use 
against communications and covers frequen- 
cies from 25 to 100 me. Because it was more 
widely used as a radar jammer, however. 
Chapter 11 contains a more detailed discussion 
of the equipment.^®"^' Its greatest application 
outside the radar held came as a GM jammer,^^! 
since it was available and since it covered the 
right frequency range with a reasonable 
amount of power. 

High-Power Airborne Jamming System 
AN/ARQ-11 

During the summer of 1944, at the request 
of the Army Air Forces, development work was 
begun on a wide-range, 1.5-kw, airborne jam- 
mer for use in the GM countermeasures pro- 
gram. This work resulted in the construction 
of ten preproduction models. It was originally 
planned to build 100 jammers, designated 
AN/ARQ-11, but in the course of military 
events, this number was deemed unnecessary 
and the construction program was curtailed. 
A ship-borne model was built, known as the 
AN/SRQ-11. 

The airborne jamming system AN/ARQ-11 
operated at frequencies between 20 and 70 me. 
It consisted essentially of a receiver and a 
self-excited transmitting oscillator.^-^ Three 
modes of operation were provided: (1) Stand 
By — the radio receiver operating and all fila- 
ments lighted; (2) Search — the power oscil- 
lator generating the unmodulated carrier at 
approximately half of the full power ; and 
(3) Operate — the power oscillator operating at 


184 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


full power and generating a carrier which is 
square wave-modulated at a frequency between 
100 and 15,000 c. The average power output 
depended on the carrier frequency — approxi- 
mately 1,700 w at 20 me and 400 w at 70 me. 

In operation, the frequency of the power 
oscillator was tuned to that of the enemy trans- 
mitter by listening through headphones to the 
difference frequency between the unmodulated 
carrier (at low power) and the enemy trans- 
mitter as the oscillator frequency was varied. 
The receiver selected and amplified this differ- 
ence frequency. When the power-oscillator 
frequency was the same as that of the enemy 
transmitter, the full power was turned on and 
the output keyed at a predetermined audio 
frequency. 

In February of 1945, one AN/ARQ-11 was 
installed in a B-24 airplane. The rear bomb bay 
of the bomber was partitioned into two com- 
partments, with the power plants for the 
ARQ-11 located in the front section and the set 
itself in the rear section. The equipment was 
satisfactorily flight-tested. 

Details of Equipment. In the production 
model, the AN/ARQ-11 equipment consisted 
of eight major units: the radio receiver 
(R-21/ARQ-11), which included five tuning 
units and weighed 24 lb with one unit in place 
(the others weighed 4 lb each) ; the audio 
oscillator (0-28/ARQ-ll), weighing 18 lb; the 
modulator unit (MD-42/ ARQ-11), weighing 41 
lb; the power oscillator (T-102/ARQ-11), 
which included seven sets of grid and plate 
plug-in coils and five antenna coupling coils and 
weighed 72 lb with one set of coils (the remain- 
ing coils weighed 13 lb) ; the three rectifier 
units (PP-130/ARQ-11), weighing 59 lb each; 
and the control unit (C-187/ARQ-11), weigh- 
ing 75 lb. The necessary cables and mounting 
trays were also included. The total weight of 
the ARQ-11 was 436 lb, exclusive of cables 
and mounting trays but including all tuning 
units and plug-in coils. The maximum power 
requirement was 46 amp at 115 v, 400 c, and 
23 amp of 28-v direct current. 

The radio receiver^^a ^gg^j with any one 

of the five plug-in tuning units which fitted 
into the front of the receiver chassis, each 
covering one of the five 10-mc bands between 


20 and 70 me. These units differed only in the 
values of some circuit elements. The input 
signal from the antenna was applied to a 
broad-band r-f amplifier followed by a mixer 
stage where it was beat against a heterodyn- 
ing signal either from the power oscillator 
or from a local oscillator included in the tuning 
unit. The audio output then went through a 
two-stage amplifier in the receiver chassis, 
which also contained a power supply. 

The audio oscillator^^^ contained a two-stage 
oscillator section, a two-stage output amplifier, 
and a power supply. It supplied an audio input 
signal for the modulator unit, with a frequency 
between 30 and 30,000 c. The modulator unit 
was arranged to control the operation of the 
power oscillator by providing the proper grid 
excitation for the three modes of operation, 
and included a clipper stage, a 3-mc local oscil- 
lator, a full-wave rectifier, an output keying 
stage, and a power supply. Control relays, 
operated from a selector in the power oscillator, 
effected the appropriate circuit changes to per- 
mit the selective operation of the set. The keyer 
system was of somewhat unconventional de- 
sign. The sinusoidal audio input was amplified 
and shaped to a square wave which was used 
to key a low-powered local oscillator ; the output 
was rectified and applied to the grids of the 
main modulator tubes. 

The power oscillator comprised a push-pull 
oscillator of the tuned grid-tuned plate type, 
and was provided with a series of plug-in coils 
permitting operation from 20 to 70 me. Each 
of the three identical rectifier units^24 contained 
a rectifier filament transformer, a plate trans- 
former, two rectifier tubes, and a filter choke. 
The outputs of the three rectifier units were 
brought into the control unit and combined in 
parallel to form the plate supply for the power 
oscillator. 

The control uniU-^ served as a power distri- 
bution point for all the ARQ-11 units and as 
a junction point for some of the interunit 
connections. Located in this unit were the relay 
system which makes the power connections, an 
overload circuit breaker and a filter section 
for the power-oscillator plate supply, pilot 
lights, controls, and all fuses employed in the 
ARQ-11. 


GUIDED MISSILES JAMMERS AND ASSOCIATED EQUIPMENT 


185 


Ship-Borne Jamming Systems and 
Amplifiers 

One jamming system requiring only very 
brief mention is the AN/SRQ-11 (XN-1). This 
is the ship-borne version of the AN/ARQ-11 
(Section 8.4.1, just preceding), of which one 
model was built.^^i equipment consisted 

of four major units: the radio receiver, the 
modulator unit, the radio transmitter, and the 
power unit. The first three units mentioned 
were virtually identical with the corresponding 
ARQ-11 units. The power unit replaced the 
control unit and the three rectifier units of 
ARQ-11. This system operated on a single 
115-v, 60-c line. 

Medium-Power Jamming System, 

Type MAS 

On April 18, 1944, the Naval Research 
Laboratory requested the engineering, develop- 
ment, and production of equipment for use as a 
countermeasure against the German HS-293 



I I 5V-60 ^ 

Figure 1. Block diagram of Type MAS ship- 
board jamming equipment for use against guided 
missiles. 

radio-controlled glide bomb^^^ and the PC- 
1400-FX radio-controlled bomb. 

The necessary jamming system was pro- 
duced and called shipboard jamming equip- 
ment, Type MAS, and the first complete unit 
was shipped on May 3, 1944. Thereafter, 49 
additional equipments were constructed, and 
47 of them were shipped between May and 
October for installation in destroyers, destroyer 
escorts, escort carriers, and transports. A 
representative was sent to England to super- 


vise installations of the equipment in several 
troop transport vessels. 

The MAS equipment shown in block form 
in Figure 1 was arranged to detect the carrier 
frequency of an enemy control signal and to 
transmit a jamming signal on the same fre- 
quency. The jamming carrier was square 
wave-modulated at 1,000, 1,500, 8,000 or 
12,000 c, and the modulation was interrupted 
for 10 msec of every 100 msec. As shown in 
the block diagram, the equipment comprised 
four major units. 

Details of Equipment. The radio receiver 
(CLU-46ADR) could detect enemy signals in 
the band from 41 to 51 me. The radio trans- 
mitter (CLU-52ADC), which was tuned to the 
enemy carrier as indicated by the receiver, 
radiated a relatively strong a-m signal with 
the modulation characteristics outlined above. 
A rectifier power unit (CLU-20ACZ) supplied 
high-voltage direct current for the operation 
of the transmitter, and a dummy load was 
provided for testing the transmitter without 
broadcasting any appreciable energy.^^^ 

The broad-band heterodyne receiver was 
designed to operate from a 70-ohm antenna 
(within a 5:1 standing- wave ratio). Although 
a local oscillator was included, the receiver 
was intended to operate primarily with a por- 
tion of the transmitter output as the heterodyn- 
ing signal. For this purpose a part of the 
radiated signal from the transmitter was 
picked up by the receiver antenna and passed, 
together with the enemy signal, through a 
broad-band r-f amplifier stage to a mixer. The 
amplified a-f beat note was applied to head- 
phones, and in operation the enemy carrier 
signal was heterodyned to zero beat for pre- 
cise tuning. 

The transmitter was tunable over the same 
range as the receiver and included a power 
oscillator, a keying oscillator, and a mechanical 
switch to interrupt the action of the keying 
oscillator for 10 out of each 100 msec. The 
power oscillator could supply either 150 w 
unmodulated r-f power or 250 (average) 
modulated power to a 50-ohm antenna system 
(within a 2 :1 standing-wave ratio) . The keying 
oscillator permitted the power oscillator to be 
modulated by square waves at any one of the 


186 


NONRADAR JAMMING TRANSMITTER TECHNIQUES 


four frequencies mentioned above. The entire 
equipment worked from a 115-v, 60-c source, 
and the control circuits allowed three types of 
operation: Stand By, Search, and Operate. 

Operation. In the operation of the MAS 
equipment, the frequency band of the expected 
enemy signals could be monitored in either of 
two ways. The controls might be set to Stand 
By, so that only the receiver was operative and 
the local oscillator was used for tuning. Alter- 
natively, the Search setting could be used, in 


controlled GM and could jam simultaneously as 
many as eight enemy signals in the band from 
46 to 51 me. 

Signals occurring in this search band were 
monitored with a superheterodyne receiver and 
presented on the screen of a cathode-ray oscil- 
loscope as individual positive pips. The receiver 
was tuned across the search band in syn- 
chronism with the horizontal sweep of the 
oscilloscope, so that the position of a pip on 
the oscilloscope screen indicated the frequency 



Figure 2. Photograph of prototype of multiple-channel jamming system, AN/SRQ-1. 


which case the power oscillator was operative 
(at low power) as well as the receiver, to pro- 
duce an unmodulated r-f signal used instead of 
the local oscillator output. In either event, after 
an enemy signal was detected and the 
carrier frequency matched, the equipment was 
switched to the Operate condition, with the 
transmitter giving full, modulated r-f power. 

Multiple-Channel Jamming System 
AN/SRQ-1 

The AN/SRQ-1 jamming equipment^^c 
developed as a countermeasure against radio- 


of the detected signal. Eight local oscillators 
provided for generating an equal number of 
independent r-f signals, whose frequencies 
could be set anywhere in the search band. The 
local oscillators could be turned on separately, 
and their signals appeared on the oscilloscope 
screen as negative pips. 

A prototype was constructed, and a photo- 
graph of its four units is shown in Figure 2. 
The receiver, timer, and cathode-ray oscillo- 
scope are in the center unit, and the bank of 
local r-f oscillators, the keyer, and the auto- 
matic power-control system in the right-hand 


GUIDED MISSILES JAMMERS AND ASSOCIATED EQUIPMENT 


187 


unit. The cylindrical unit in the foreground is 
the r-f power amplifier and the left-hand unit 
contains the several power supplies required 
for the operation of the equipment. 

Operating Details. In the operation of the 
equipment, one local oscillator was turned on 
for each enemy signal detected and its fre- 
quency adjusted until the negative pip coincided 
visually with a positive pip. More precise fre- 
quency matching was accomplished by means 
of an aural-monitoring channel, in which each 
of the local-oscillator signals in turn beat 
against the received signal ; the local oscillator 
frequency was then adjusted to obtain an a-f 
beat note with the enemy signal to which it 
was most closely tuned. The locally generated 
r-f signals, each tuned accurately to an enemy 
transmission, were then amplified and radiated. 

If the local r-f signals, however, had been 
transmitted continuously, the jamming signal 
would have made further search and monitor- 
ing impossible. Accordingly, search and jam- 
ming periods were alternated at a cyclical rate 
of 10 c, the jamming period occupying 90 per 
cent of each 100-msec cycle. This repetition 
rate was high enough that the visual presenta- 
tion of the signals on the oscilloscope appeared 
continuous. The search-jam cycle was produced 
by a timer which first permitted operation of 
the oscilloscope and the aural-monitoring chan- 
nel for 9 msec, then turned on the jamming 
equipment for 90 msec, and finally provided 
a 1-msec delay period in which the receiver 
circuits could recover from the overload im- 
posed by the jamming signal. 

In the operation of the transmitter the sig- 
nals from the local oscillator were combined, 
keyed at one of four audio frequencies, and 
applied to a linear r-f power amplifier. The 
keying circuit square wave-modulated the 
combined r-f signals optionally at 800, 1,000, 
10,000, or 12,000 c. The power amplifier was 
linear, to avoid mixing and the consequent 


radiation of power at the unwanted sum-and- 
difference frequencies. It provided uniform 
response over the band from 46 to 51 me with 
an average output of 10 w. Since the input 
signal components might add in amplitude and 
overload the amplifier, an automatic power- 
control system was provided to maintain the 
input at a low enough level to preserve the 
linearity of the amplifier. In this control sys- 
tem, part of the amplifier output operates a 
servomotor, which in turn adjusts an attenua- 
tor in the input circuit. 

1-KW Airborne or Ship-Borne Amplifier 

At the request of the Army Air Forces, work 
was started on the development of a 1-kw 
amplifier for airborne or shipboard use against 
GM. This amplifier was to be capable of cover- 
ing any 5-mc band in the 40- to 60-mc range and 
was to be driven by the modulator unit being 
designed for the AN/SRQ-1. 

The project was terminated before comple- 
tion; however, several experimental amplifiers 
were built to test various types of power tubes 
and associated broad-band circuits. The pre- 
liminary performance figures for several tube 
types in push-pull at 50 me are given below: 

833-A Bandwidth 7 per cent, peak efficiency 
48 per cent. 

304-TL Output 700 w at 60 per cent plate 
efficiency ; 10 per cent variation in output power 
at 10 per cent bandwidth. 

8014-A Output 1,100 at 50 per cent plate 
efficiency ; 20 per cent variation in output power 
at 12 per cent bandwidth. 

827-R Output 2,000 w at 65 per cent plate 
efficiency; bandwidth about the same as for 
8014-A. 

8002-R Output 2,700 w, amplifier efficiency 
55 per cent; 15 per cent variation in output 
power at 10 per cent bandwidth. The power 
output of this amplifier was limited by the 
power supply. 


Chapter 9 

NONRADAR ANTIJAMMING TECHNIQUES 


INTRODUCTION 

T he development and use of antijamming 
[AJ] techniques and equipment is related 
to radio countermeasures [RCM], since AJ is 
in effect a counter-countermeasure. Studies of 
the vulnerability of Allied equipment to both 
friendly and enemy jamming techniques re- 
sulted in the development of certain AJ prac- 
tices. It is important to recognize the fact that 
it is generally impossible to protect a specific 
communications channel or set against a con- 
certed and properly directed jamming attack. 
The AJ precautions should therefore be con- 
sidered from the viewpoint of the whole com- 
munication network for a given area. 

Probably the most important basic considera- 
tion in AJ techniques is adequate operator 
training and experience. There is no substitute 
for the ability and will to overcome jamming. 
For several of the more generally effective 
forms of interference, such training is the most 
effective AJ measure yet developed. 

This chapter summarizes the various projects 
established at laboratories under the auspices of 
Division 15 which were concerned with AJ tech- 
niques for equipment other than radar and with 
tests made to measure the vulnerability of such 
equipment to jamming. Most of the work was 
carried out by the Federal Telecommunications 
Laboratories, Inc., under contracts OEMsr-936 
and OEMsr-937, the Airborne Instruments 
Laboratory under contract OEMsr-1305, Jansky 
and Bailey under contract OEMsr-1024, and the 
Radio Corporation of America under contract 
OEMsr-895. 

Many of the fundamental AJ considerations 
are the same whether the equipment to be pro- 
tected is a radar or some other electronic de- 
vice; this is especially true of the conclusions 
as to the importance of operator training. The 
radar AJ techniques developed are described in 
Chapter 13, while Chapter 10 includes some 
considerations on the protection of proximity 
fuzes. The jamming techniques against which 


the equipments are to be protected are de- 
scribed in Chapter 8 and also in Chapter 10. 


9 2 GENERAL ANTIJAMMING STUDIES 

In the course of the AJ program, a certain 
amount of attention was given to basic AJ prin- 
ciples, which do not involve the use of any par- 
ticular apparatus but are concerned with the 
proper design and employment of equipment. 
In addition, general studies were made to de- 
termine the effects of various jamming signals 
on the different types of receivers and circuits. 
Descriptions of the jamming signals used can 
be found in Sections 8.2.2 and 13.3, together 
with some conclusions on their effectiveness in 
general. Special studies were carried out on the 
AJ properties of detectors and mixers. The re- 
sults of this work were of considerable help in 
evaluating the effectiveness of proposed jam- 
ming methods (see Section 8.2). 

The results of these general studies were 
collected, together with the results of the vul- 
nerability measurements described in Section 
9.3, and compiled to form a Handbook of Com- 
munications AJ. 288 . 344 q’hig handbook was in- 
tended largely for the use of receiver designers, 
in order that they might avoid design practices 
which have proved to be bad from an AJ stand- 
point. The compilation was begun by the Com- 
munications Section of the Division 15 AJ Prac- 
tices Panel (see Section 13.2.1), and was com- 
pleted by Jansky and Bailey. 


Basic AJ Principles 

There are two fundamentals to be remem- 
bered if equipment is to be properly protected 
from enemy jamming. The first is that the 
equipment should be well-designed from an AJ 
point of view — that is, the vulnerable types of 


188 


GENERAL ANTIJAMMING STUDIES 


189 


circuits should be avoided. The results of the 
investigations into the relative susceptibility of 
different circuits are summarized in the later 
paragraphs of this section. 

The second fundamental is that the equip- 
ment should be used in such a way as to render 
jamming as difficult as possible and to nullify 
the effects should it occur. For example, in 
selecting the site for a station, consideration 
should be given to the possibility of enemy 
jamming, in addition to the usual precautions. 
Communications systems in the higher-fre- 
quency bands should be located so that they are 
screened against jamming from enemy-con- 
trolled territory. This is not always possible, of 
course, but the technique should be kept in 
mind. 

Frequency Coverage 

The coverage of a communications network 
should be planned with the idea of providing the 
required service in the area involved in spite 
of the anticipated amount of enemy jamming. 
In other words, consideration of the AJ prob- 
lem should not be limited to the study of single 
pieces of equipment at particular sites, since, 
if a set is within range of the enemy, it can 
almost certainly be put out of action if the 
enemy concentrates his efforts on it. 

The important consideration in planning serv- 
ice for a given area is to provide both flexibility 
and diversity of frequency. The latter may be 
achieved by using equipment, for each type of 
service, which operates in widely separated fre- 
quency ranges, so that if one channel is jammed 
another may be used. Frequency flexibility in- 
volves the means for selecting a number of 
different operating frequencies in a given range. 

Although frequency diversification cannot al- 
ways be achieved, it is highly desirable, and this 
fact should be kept in mind in any plan affect- 
ing large areas. When equipments operating in 
a new portion of the spectrum are added to net- 
works already in use, the older sets should not 
be removed from service, both in order to have 
various channels available and to keep from 
revealing the presence of new apparatus on 
other frequencies. 

Moreover, it is important to use the whole 
band of frequencies over which a given type of 


equipment can operate. This practice forces the 
enemy to spread his jamming effort over a 
wider band and thus reduce the strength of the 
interference in any given channel. The ability 
to make small (or large) changes rapidly in 
the operating frequency of a set is also im- 
portant, since this makes it possible to tune the 
set away from the jamming to a region where 
the interference is less effective or absent. 

Operator Training 

The importance of training operators prop- 
erly can hardly be overemphasized (see Sections 
9.3 and 13.5). The training should include not 
only instruction in the use of the various AJ 
devices and attachments which may be avail- 
able, but continual experience in reading 
through jamming and in the proper use of the 
controls available on the equipment. It has been 
proved by actual operations in World War II 
that the efficiency of operators is greatly re- 
duced the first time they are exposed to jam- 
ming, but that it improves steadily with 
successive exposures. This experience can be ob- 
tained, obviously, at less cost during training 
than in battle. 

In all communications sets, the operator has 
a variety of controls at his disposal, and it is 
essential that he be familiar with their use in 
order to minimize the effects of interference. 
Often what might be considered abnormal ad- 
justments (especially of the receiver gain con- 
trol) result in improved AJ properties. For ex- 
ample, limiting action in communications re- 
ceivers greatly decreases the effectiveness of 
spark and f-m jamming; but many receivers 
do not have limiting circuits. By turning up the 
volume controls, however, limiting action can 
be obtained by overloading the receiver, the 
headphones, or even the ear. 

The training of operators is materially aided 
by the use of suitable phonograph records, and 
jamming signal generators are also important 
training adjuncts. The use of these aids should 
not be limited to schools, for it is only by con- 
stant exposure to jamming that an operator 
gains and maintains his ability to work through 
interference. Such devices, therefore, should be 
made available to operators and used periodi- 
cally for training. 


190 


NONRADAR ANTIJAMMING TECHNIQUES 


Comparison of Communications 
Systems 

A number of tests were made comparing the 
relative communication efficiencies of an a-m 
system, a wide-band f-m system, a narrow-band 
f-m system, and a telegraph system; the com- 
parison was made on the basis of readability 
through interference consisting of random 
noise, impulse noise, and continuous wave.®^ 
These studies indicated several modifications 
which could be used to improve reception in the 
presence of jamming. One was the insertion of 
an audio limiter in the modulation input of the 
transmitter, to increase the average modulation 
level.®^ This change produced about 6 db im- 
provement for amplitude modulation in the 
presence of random and impulse noise. For other 
systems and types of interference, the improve- 
ment effected was small. Another arrangement 
which was useful under certain conditions of 
interference was a narrow-band f-m adapter.®”^ 
Such an adapter, with an i-f bandwidth of ap- 
proximately 8 kc, was designed specifically to 
be used with the Signal Corps radio receiver 
BC-603D. While the use of this AJ device re- 
sulted in a small sacrifice in speech reproduc- 
tion quality, there was little impairment in the 
intelligibility. Prototypes of the narrow f-m 
adapter were delivered to the Signal Corps. 

^ Jamming of Telegraphy 

An investigation was made to determine the 
best conditions for jamming telegraphy and the 
best possible protection against such jam- 
ming.159 . 160 Previous tests had indicated that 
the jamming of telegraphy was a difficult prob- 
lem. A very extensive study was conducted with 
a large number of different types of jamming 
signals at audio frequencies, at radio frequen- 
cies, with and without limiters, and with actual 
Army and Navy communications sets,^®^ well 
as with laboratory equipments. The tests cov- 
ered both barrage and spot-frequency jamming. 
The types of interference used included re- 
sistance noise, multiple tones, variable-pitch 
sawtooth jamming, random pulses similar in 
character to telegraphic code, and so forth. 

The research was also concerned with the 


human factors, such as experience of the op- 
erator, fatigue, nervous reactions to different 
types of noise, etc. 

Results Obtained 

All the experiments indicated that results 
can be reproduced accurately when confined to 
laboratory tests and that jamming efficiency 
can be defined when the human factor is elimi- 
nated. In these conditions, the determining fac- 
tor is not the type of jamming signal used but 
the accurate tuning of the carrier frequency. 
Only signals within 20 c of the carrier fre- 
quency have any appreciable effect. Resistance 
noise is probably the most effective modulating 
signal,^®^ but other types of modulation are 
almost as efficient when the carrier is properly 
tuned. 

The introduction of limiters in a receiver does 
not protect against jamming if the jammer is 
modulated with ‘ffindistorted” resistance noise. 
By “distorted” resistance noise is meant noise 
signals which have been submitted to nonlinear 
effects such as clipping or saturation. Distor- 
tions like these, which change the frequency 
spectrum of the noise, might reduce the effi- 
ciency of the jammer in significant proportions 
when the receiver is protected by limiters. 
When no limiters are introduced, even distorted 
noise is effective. 

Most of the results obtained in the laboratory 
are reproducible in actual practice with one con- 
siderable difference — the experience of the op- 
erator. An experienced operator represents a 
protection against jamming which can be esti- 
mated at roughly 12 db, plus an additional 
factor of 6 to 8 db which represents the differ- 
ence in susceptibility to fatigue. This fatigue 
factor is due to the fact that even an experi- 
enced operator loses some of his ability to 
distinguish signals through noise after 20 or 
30 min of jamming but that for an inexperi- 
enced operator such an effect does not exist. 

All these factors are true only when jamming 
is not complete. Technically, it is possible to ob- 
tain complete jamming of telegraphy with a 
very good efficiency (i.e., with equal field 
strength for the jammer and the desired signal) 
if absolutely accurate frequency tuning can be 
achieved.^®^ 


VULNERABILITY OF COMMUNICATIONS RECEIVERS 


I9I 


Jamming of Pulse Communications 

A general study was carried out to investi- 
gate the jamming and antijamming possibilities 
of pulse communications systems.^^^ The in- 
vestigations, in general, were concerned with 
voice-modulated communications systems using 
modulation of the pulse frequency or phase. The 
pulses were usually about 0.8 to 1 psec in 
length, and the repetition rate was in most 
cases either 10 kc or 18 kc in the unmodulated 
condition. 

Scope of Experiments 

In the systems employing modulation of the 
pulse frequency, the peak deviation due to the 
frequency modulation was about 4.5 kc when 
the 10-kc rate was used ; for the 18-kc rate, the 
peak deviation was about 12 kc. In the pulse 
phase-modulation system, pulses approximately 
0.8 psec long were employed at a 10-kc repeti- 
tion rate and were modulated approximately 
one-quarter of a radian by voice.^^ 

The various types of jamming signals tried^^^ 
included: (1) continuous wave unmodulated or 
continuous wave amplitude-modulated 100 per 
cent with a-f random noise; (2) short pulses, 
unmodulated or frequency-modulated with a-f 
random noise, at various pulse rates ; (3) pulses, 
phase-modulated with a-f random noise using 
mark factors of 2, 30, and 50 per cent; (4) a 
radio spectrum of random noise both gated and 
not gated. 

Results and Conclusions 

Several types of receivers were used, includ- 
ing a trigger-type circuit as well as a normal 
limiter and discriminator system. Although the 
trigger-type circuit made a highly desirable re- 
ceiver from the standpoint of simplicity and 
ability to receive wide deviations, it was easily 
jammed, since interfering pulses would trip the 
trigger circuit. 

An important improvement in the AJ fea- 
tures of pulse receivers was a pass circuit or 
pulse-amplitude selective circuit. This pass cir- 
cuit was combined with an automatic gain 
control circuit, so that the receiver was selec- 
tive to only a narrow range of pulse amplitudes 
and pulses of higher or lower amplitude were 


not transmitted. The method was a very effec- 
tive AJ device.^^^ 

In order to obtain the full advantage of the 
noise reduction possible with a pulse f-m sys- 
tem, the i-f amplifier was followed in some cases 
by clipper stages. These were circuits which 
took a horizontal slice out of the center portion 
of the pulse, thus removing amplitude varia- 
tions and noise between pulses as long as the 
amplitude of the pulse was above the threshold 
level. The threshold level was taken as the point 
where the peak amplitude of the pulses was 
twice that of the noise. The pulses from the 
clippers were differentiated to remove the width 
variations caused by random noise^^® and were 
then used to trigger a pulse-lengthening circuit. 

The best method for jamming a pulse com- 
munication system is, of course, the one which 
uses the least power to accomplish the jamming. 
The power required for complete jamming is 
quite variable, depending upon circuit arrange- 
ments, and there is no best method unless the 
circuit details of the victim receiver are known. 
On the average, when this knowledge is un- 
available, the best jammer was found to be the 
r-f noise spectrum with 50 per cent gating. The 
most effective method found for reducing the 
susceptibility of a receiver to jamming was the 
pass circuit. The receiver for f-m pulses should 
employ differentiation and either a balanced- 
type discriminator or an unbalanced-type dis- 
criminator with a good limiter, whichever is 
most convenient for a particular case. It was 
found helpful to have a gain control on the i-f 
amplifier and adjustments on the clipper stages. 

In addition to the pulse jamming and AJ 
studies, a preliminary report was prepared cov- 
ering the detection and identification of various 
possible systems of pulse communication, and 
the measurement of variables such as the aver- 
age pulse rate, the pulse length, and the type of 
modulation.^^^ 


9 3 VULNERABILITY OF COMMUNICA- 
TIONS RECEIVERS 

A great many measurements were made of 
the vulnerability to jamming of the radio com- 
munications circuits and receivers used by the 


192 


NONRADAR ANTIJAMMING TECHNIQUES 


Armed Services. Similar measurements made 
on enemy communications sets are discussed in 
Chapter 8 (Section 8.2.3), and those on United 
States radars in Chapter 13 (Section 13.4.1). 
Any AJ measures encountered or developed in 
the course of this work or suggested by the 
results were of course reported. No special 
equipment was developed in such investigations 
except what was necessary to conduct special 
jamming tests. 

In order to carry out the test program, a 
separate laboratory was set up in Washington, 
D. C., by making alterations to an existing 
building. Special rooms which were individually 
shielded and soundproofed were constructed; 
general laboratory and office space was provided 
as well, to permit all the work to be concen- 
trated at one location. The facilities were suf- 
ficient to provide for measurements on several 
types of equipment by different groups or for 
the simultaneous testing of as many as four 
different receivers with a single transmitter- 
jammer setup. 


Test Methods and Techniques 

When the work was started, there was no in- 
formation available as to the type of jamming 
signals which might be encountered ; it seemed 
reasonable, therefore, to use those signals which 
were easily obtainable in the field as well as 
those which were to be used against the enemy. 
As a result of this policy, all vulnerability tests 
were made using the following signals as inter- 
ference: (1) continuous wave, (2) continuous 
wave amplitude-modulated by sine wave, step 
tones (Bagpipes), and noise, (3) f-m continu- 
ous wave using sine-wave, step-tone, and noise 
modulations, all with different frequency devia- 
tions to give a variety of bandwidths, (4) wide- 
sweep f-m signals giving barrage jamming to 
cover bands from 1 to 4 me wide, and (5) pulses, 
with various widths and repetition rates. 

In order to obtain the various jamming sig- 
nals, special signal generator equipment was 
required, and most of this was provided by the 
General Radio Company under contract OEMsr- 
1005 (see Section 5.2.1). In addition, it was 
necessary to build a pulser which gave cali- 


brated pulse voltages over a frequency range 
from 2 to 150 me with output levels up to 20 
or 25 V into a 75-ohm load. Details of the meth- 
ods for making the vulnerability tests are de- 
scribed in the various references given below. 
In general, the method was as follows: the 
jammer and the desired signal were introduced 
in the input of the receiver through mixing 
boxes, and the relative levels carefully set for 
the desired conditions. In cases where a receiver 
operated normally with a certain type of trans- 
mitter, the desired signal was obtained from 
this transmitter with the output suitably at- 
tenuated for the test. 

Considerable study was made to determine 
the most suitable type of intelligibility tests to 
be used, with the result that the following cri- 
teria were established: (1) For code tests em- 
ploying modulated or unmodulated continuous 
wave, transmission of five-letter unpronounce- 
able groups was made at a rate of ten words per 
minute, and the jamming effectiveness was 
rated as the percentage of code groups missed 
out of a total of 20 groups for each test; a 
group was considered incorrect if two char- 
acters or more were missed. (2) For voice com- 
munication, each test consisted of ten sentences 
of a certain type.®^^ The jamming effectiveness 
in this case was taken as the percentage of test 
sentences incorrectly received, where the de- 
termination of correct or incorrect reception 
was based on whether or not the listeners under- 
stood the thought contained in the sentence and 
could repeat the key words. In general one 
talker and two listeners were used for each 
test. Definitions and test methods for jamming 
effectiveness testing were agreed upon jointly 
by members of the research groups most closely 
connected with the problem .262 

Results of Tests 

It was found that, in general, the communica- 
tions equipment in use by the Armed Services 
can be divided for the purpose of vulnerability 
studies into the following six broad groups. 

1. High-frequency a-m equipment: general- 
purpose fixed and mobile sets employing ampli- 
tude modulation for both voice and code com- 
munication, in the frequency range 1.5 to 18 
me. 


VULNERABILITY OF COMMUNICATIONS RECEIVERS 


193 


2. Very-high-frequency a-m equipment : v-h-f 
aircraft and ground-to-air sets employing ampli- 
tude modulation for voice communication, in the 
range 100 to 150 me. 

3. High-frequency f-m equipment: mobile 
and hand-transportable sets employing fre- 
quency modulation for voice communication, in 
the frequency range 20 to 50 me. 

4. Very-high-frequency f-m equipment : point- 
to-point and relay equipment using frequency 
modulation for voice, facsimile, and teletype 
printer, in the range 50 to 100 me. 

5. Pulse systems : sets using a series of pulses 
whose phase or repetition rate is modulated for 
voice communication. 

6. Special equipment: communications sys- 
tems specifically designed to have good AJ char- 
acteristics, and special-purpose equipment, such 
as mine detonators. 

Group (1) : High-Frequency 
Amplitude-Modulated Receivers 

The jamming susceptibility of the following 
receivers in group (1) was investigated: the 
BA-348-R,268 the BC-342-N,27o the BC-312-N,27« 
the BC-652-A,2-2 the BC-669-C,273 the BC-654- 
A,27^ and the ARB.-^^’-®^ A comparison was 
made of the vulnerability of all but the last of 
these receivers.^^^ 

In general, the results can be described as 
follows. An unmodulated carrier was not an 
effective jammer even when detuned to give an 
audible beat. Ordinary amplitude modulation 
with a fixed tone (sine wave), particularly when 
detuned by an audible beat, caused jamming to 
occur at jam-to-signal [J/S] ratios of 6 to 14 
db. Jammers amplitude-modulated with noise 
were approximately 10 db less effective than a 
pure tone, whereas step tones were most effec- 
tive when detuned approximately 1 kc, con- 
sistently giving J/S ratios of 4 to 8 db. Jammers 
frequency-modulated with noise or step tones, 
and having bandwidths of the same order of 
magnitude as the receiver, were most effective, 
causing jamming at J/S ratios of approximately 
0 db (i.e., jamming strength equal to signal 
strength). Pulses were relatively ineffective 
against receivers of this type; although they 
often caused discomfort to the listeners, it could 
be alleviated by proper installation of a good 


peak limiter. As expected, c-w and modulated 
c-w communication was superior to voice 
against all of the jammers employed. 

Group (2) : Very-High-Frequency 
Amplitude-Modulated Receivers 

The vulnerability of four different receivers 
in group (2) was studied; namely, the AN/ 
arc-4,264 the BC-639-A,265 the BC-624-AM,266 
and the AN/ARC-l.^^^ A comparisons®^ of the 
first three of these was carried out. In addition, 
a series of tests was made on the BC-624-A to 
determine the vulnerability to pulses, as affected 
by the use of various types of limiters.^®® 

Receivers in this frequency range were char- 
acterized, in general, by greater bandwidths 
than those in the lower-frequency ranges, and 
they were therefore somewhat more vulnerable 
to jammers whose energy was distributed over 
a considerable portion of the spectrum. To offset 
this drawback, the greater bandwidths made 
peak clippers more effective against impulse- 
type noise; and such clippers were found in all 
the sets listed above except the BC-639-A. The 
vulnerability of these receivers to c-w and to 
a-m signals was much greater than was that 
of the receivers in group (1), but it was sus- 
pected that the cause was random instability 
in the jammers at these frequencies. This hy- 
pothesis was verified by tests on one of the re- 
ceivers in group (1) (the ARB), using a special 
signal which consisted of continuous wave fre- 
quency-modulated to a very small degree by 
four tones of about 200 c and one of approxi- 
mately 500 c, the maximum deviation in no case 
being more than 500 c. This signal jammed the 
ARB receiver at a J/S ratio somewhat less than 
0 db, which is similar to that observed on the 
v-h-f sets. The jamming effectiveness was 20 
per cent at a J/S ratio of —17 db.^^® 

An additional study was made of the AN/ 
ARC-1. Several modifications were suggested to 
reduce the noise in the set at low signal levels. 
It was found that the excessive noise was caused 
by overly rapid AVC action in the r-f stage.^®^ 

Group (3) : High-Frequency 
Frequency-Modulated Receivers 

The receivers tested under group (3) were 
the BC-603-D,258 the SCR-609-A,259 and the 


194 


NONRADAR ANTIJAMMING TECHNIQUES 


SCR-300-A.263 Pulse and wide-sweep f-m sig- 
nals were found relatively ineffective against 
these f-m sets, because of the inherent limiting 
which is a part of the f-m system. Jammers 
using frequency modulation with bands com- 
parable to the receiver pass band were as effec- 
tive against these sets as against a-m equip- 
ment. Jammers with c-w and a-m signals were 
also effective, although careful tuning of the re- 
ceiver helped to improve reception. The effec- 
tiveness of these latter types of jammers 
against f-m equipment was due to a “capture” 
effect associated with f-m communication. Vari- 
ous methods of eliminating this effect were in- 
vestigated and reported.2^^’ It was found that 
a gain of 18 db to 30 db (depending upon the po- 
sition of the jammer in the pass band) could be 
obtained by the installation of an automatic 
back-biasing arrangement, to be switched in 
when such interference was encountered. 

Group (4) : Very-High-Frequency 
Frequency-Modulated Receivers 

Two sets of this type were studied. The first 
of these was the AN/TRC-1, which exhibited 
characteristics very similar to those of the 
group (3) receivers, particularly as regards vul- 
nerability to c-w and a-m signals.^^i The four 
audio channels of this multiplex system pro- 
vided a means of reducing the effect of jamming 
due to audio masking, in cases where the audio 
interference was concentrated in a limited por- 
tion of the audio spectrum. 

Facsimile and teletype were in general more 
vulnerable than voice systems (but see Section 
9.5). The second set studied in group (4) was a 
facsimile system^^ in which a relatively narrow- 
band a-m receiver was used in conjunction with 
a wide-band f-m transmitter modulated by a 
black and white picture signal. The receiver de- 
tected a pulse each time the f-m signal swept 
through its narrow pass band; thus, in effect, 
only the edges or transients of the original pic- 
ture were recorded. Studies were made using 
both audio and radio frequencies. The results 
indicated that the loss in detail inherent in this 
“Transient System” was not counterbalanced by 
the improved signal-to-noise ratio. That is, the 
best compromise obtainable compared unfavor- 
ably with existing methods. Moreover, the Tran- 


sient System required very precise background 
operating adjustments. 

In addition to the above, some tests were 
made on the AN/TRC-8. Vulnerability measure- 
ments could not be made on it for lack of test 
equipment covering the frequencies near 250 
me where it operates, but sufficient information 
was obtained to indicate that the results of such 
tests would not be substantially different than 
for the other voice f-m receivers.-®^ 

Group (5) : Pulse Systems 

This group includes all the pulse communica- 
tion systems in use by the Armed Services (see 
Section 9.2.4). The initial susceptibility study 
was made on the AN/TRC-5 system.^^® The 
power required to produce jamming in this set 
was determined for a pulse jammer using sev- 
eral values of pulse length and frequency. The 
most effective jamming occurred at a pulse rate 
near 10 kc with pulse lengths of 1 or 2 |isec. 
Measurements were also made of the jamming 
power required with continuous wave and with 
a wide-band fluctuation noise spectrum. The 
results of these measurements were applied in 
a calculation of coverage to find the distances 
and angles over which a jammer with 100-w 
radiated power could produce interference on 
a radio circuit set up for maximum link dis- 
tances. In general, it was concluded, the jam- 
ming source would have to be airborne and 
situated within a narrow range of angles, so 
that it would be difficult for an enemy with 
inferior air power to jam the system effectively 
over any appreciable length of time. Means for 
possible AJ measures were studied. 

Some experiments were made on an arrange- 
ment to demodulate a selected channel of a time- 
division multiplex signal, such as that of the 
AN/TRC-5. This method used a photocell pickup 
from the image on a cathode-ray oscilloscope. 
The pip of the desired channel excited the 
photocell through a suitable mask on the oscillo- 
scope, and, after proper amplification, an audio 
signal resulted. The frequency characteristic 
of the fluorescent screen was such that the 
higher audio frequencies were greatly reduced, 
and consequently a high degree of compensa- 
tion was needed in the audio amplifier. 

The system resulted in an audio signal with a 


VULNERABILITY OF GUIDED MISSILE AND ALTIMETER SYSTEMS 


195 


noise level which was fairly high but reasonably 
intelligible when used in conjunction with a 
5-in. laboratory oscilloscope having fairly good 
brilliancy. The system was unworkable with the 
image obtained on the oscilloscope of the 
AN/APA-11 radar indicator assembly, because 
of insufficient light intensity. 

Group (6) : Special Systems 

Several AJ modifications to standard sets, 
which might be considered under this head, are 
discussed briefly above in conjunction with the 
unmodified sets. Other special AJ systems are 
described in Sections 9.5.2 and 9.5.3. 

In addition to these studies, vulnerability 
tests were made on the receiver AN/TRR-2 as 
operated by the transmitter AN/TRT-1 for the 
purpose of selective mine detonation.^®^ The set 
was found to be extremely susceptible to any 
simple jamming action, because it involved the 
use of tone selection and impulse keying com- 
bined with a superregenerative receiver. The 
jamming would not be expected to cause false 
operation but could prevent operation when 
required. 


Conclusions and Recommendations 

The results of the tests made to date on all 
equipment show that there is no universal pal- 
liative to make sets less vulnerable to jamming 
signals of all types. This fact is due to the 
nature of the intelligence to be conveyed. In 
addition to the actual existence of the complex 
transient, the general character must be pre- 
served; it is therefore impossible to discrimi- 
nate against jamming in favor of the desired 
signal when they are of the same character. On 
the other hand, the proper use of the limiter 
and attention to the time constants of the vari- 
ous receiver circuits can make sets less vul- 
nerable to pulse interference, while careful at- 
tention to the circuit elements which improve 
the stability of the equipment as well as its 
overall performance results in a set which is 
less susceptible in general. 

These results indicate that the continued 
study of specific equipments would be less valu- 
able than a detailed study of special components. 


such as converters, r-f and i-f amplifiers, and 
detectors. It would also be valuable to continue 
tests on equipment which incorporates design 
features of an unusual nature, particularly 
those which are specifically designed to counter- 
act jamming. 


VULNERABILITY OF GUIDED MISSILE 
AND ALTIMETER SYSTEMS 

A number of measurements were made of the 
jamming susceptibility of guided missile [GM] 
and radio altimeter receivers. The techniques 
and test methods used in these studies were 
similar to those described in the preceding sec- 
tion on communications receivers. 


Guided Missile Receivers 

A considerable amount of work was done on 
the testing of typical GM receivers when sub- 
jected to various types of jamming signals. 
Among the types tested were the Azon, Razon, 
GB-4, AN/ARW-2, AN/SRW-2, and Hs-293 
receivers. The last of these was a German equip- 
ment. 

Remote-Control System 

The AN/SRW-2 (XA-1) receiver forms, in 
combination with the AN/ARW-33 (XA-1) 
transmitter and associated channel multiplica- 
tion equipment, a remote-control system for 
guiding distant objects and performing certain 
other functions. An investigation was made of 
the vulnerability of this receiver to jamming.^^'^ 

The results showed that the equipment was 
extremely vulnerable to c-w jamming, because 
the control signals are tones which must be 
selected by filters in the receiver. It was also 
found to be highly susceptible to pulses ; certain 
modifications which were tried, however, im- 
proved the operation against pulses a great deal. 

Enemy GM-Control Receiver 

During the first months of 1944, jamming 
tests were conducted on three different mockups 
of the Hs-293 receiver. The first of these copies 
was completed when only very sketchy informa- 


196 


NONRADAR ANTIJAMMING TECHNIQUES 


tion concerning the enemy receiver was avail- 
able.^^- As more detailed information on the 
circuits was obtained, the succeeding models 
were built, each to more accurate specifications 
than the preceding one. When the third model 
was completed, most of the jamming tests 
which had been made on the prior models were 
repeated on it. 

Two general types of experiments were per- 
formed in these jamming tests. The first con- 
sisted of field tests made with transmitters as 
the sources of jamming and control signals. The 
second consisted of laboratory bench tests with 
signal generators as the sources. In all cases, 
the jamming criterion used was simply that the 
first relay in the aileron channel of the Hs-293 
receiver be prevented from following the alter- 
nations of the control signal modulation. 

Of the various possible methods investigated 
for jamming the Hs-293 receiver, the only one 
which did not require prohibitive amounts of 
power was spot jamming with modulation at 
one of the missile-control frequencies. The fol- 
lowing types of jamming, listed in order of de- 
creasing efficiency, appeared to be too inefficient 
as to power requirements to be practical: (1) 
50-kc f-m barrage amplitude-modulated at a 
missile-control frequency; (2) two jamming 
signals with a frequency difference equal to the 
intermediate frequency of the receiver; (3) 
spot jamming modulated by pulses of short duty 
cycle and high peak power; (4) mechanical f-m 
barrage at a random frequency; and (5) un- 
modulated spot jamming. 

Enemy Tank-Control System 

A comprehensive study was made of the radio 
control system of a captured German BlVb 
tank.31^ found possible to work out the 

control system of this tank in quite complete 
detail (see also Chapter 15). 


9.4.2 Frequency-Modulated Altimeters 
and Bombsights 

The vulnerability of f-m radio altimeters and 
bombsights was estimated on the basis of labo- 
ratory tests conducted with four equipments, 
the U.S. AN/ARN-1 and AN/APN-1 altim- 


eters, the German FUG. 101 altimeter, and 
the U. S. AN/APG-4 low-altitude bombsight. 

Radio Altimeters 

A study was made on the jamming suscepti- 
bilities of the three f-m radio altimeters listed 
above.^2^' In the laboratory it was possible 
to determine the amount of jamming signal re- 
quired at the altimeter receiving antenna to 
cause the unit to be jammed. The very im- 
portant problem of antenna patterns and the 
merits of various jamming locations could not 
be investigated properly without full-scale tests 
in the field. 

In spite of the protection against modulated 
jamming signals provided by the balanced de- 
tector in the American altimeters and the 
square law detector in the FUG.lOl, it was 
found that the most effective interference was 
a sinusoidal a-m carrier tuned to within 25 me 
of the center frequency of the altimeter trans- 
mitter. The reading of the altitude indicator in 
one of these f-m altimeters was determined by 
the frequency of the audio beat which resulted 
from mixing the transmitted signal and the 
delayed ground echo. To override this audio 
voltage, therefore, and cause the altimeter to 
indicate an erroneous altitude, the audio modu- 
lation on the jammer had to be fixed at the 
frequency corresponding to the erroneous read- 
ing desired. 

In general, two types of altimeter jamming 
were considered. The first was the jamming of 
low-flying aircraft or of guided missiles de- 
pendent on a radio altimeter to maintain them 
at the desired low altitude.^^^ In this case it was 
best to make the altimeter indicate a higher 
altitude than correct and thus possibly cause 
the plane or missile to fly into the ground or 
water. The laboratory measurements showed 
that to accomplish this result the jamming field 
strength at the altimeter receiving antenna had 
to be approximately 5 times the echo field 
strength there for the American altimeters, 
but only 1.5 times the echo for the FUG.lOl. 
These figures were based on an aircraft flying 
at an original altitude of 100 ft. 

A second type of jamming was required when 
the altimeter was used as a proximity detonat- 
ing device in large missiles^^^ (see Chapter 10). 


RADIO-PRINTING SYSTEMS 


197 


In this case, it was desirable to cause the altim- 
eter to read low as the missile approached its 
detonating altitude, thus producing a prema- 
ture explosion. It was found that such “down- 
ward” jamming required considerably more 
jamming power. To jam an altimeter down to 
a reading of 100 ft when the instrument was 
flying at an altitude of 1,000 ft required a 
jamming signal strength about 400 times the 
echo signal strength in the altimeter receiving 
antenna, in the case of the American altimeters, 
and about 16 times the echo, in the FUG.lOl. 
In general, the FUG.lOl was found to be con- 
siderably more vulnerable than the American 
altimeters; but even with its comparatively 
high vulnerability, the power necessary to jam 
the FUG.lOl (assuming simple antenna pat- 
terns) varied from several hundred to many 
thousand watts. 

Vulnerability of Bombsight 

An investigation was made of the vulnerabil- 
ity of the AN/APG-4 low-altitude f-m bomb- 
sight. In the laboratory, measurements were 
made to determine the relative effectiveness of 
jamming signals and the amounts of such sig- 
nals required to cause failure of the APG-4. It 
was found that the most effective jamming was 
produced by a carrier, amplitude-modulated at 
about 3,000 c and tuned to within the f-m band 
of the APG-4 transmitter. The same jamming 
signal was found to be only slightly less effec- 
tive if detuned as much as 40 me from the 
APG-4 center frequency. The unmodulated jam- 
ming carrier was found to be considerably less 
effective and indeed had no jamming effect 
unless tuned to a frequency within the 5-mc f-m 
band of the APG-4. 

Full-scale jamming tests were conducted 
against a corner reflector. The AN/APG-4 was 
installed in an airplane and provisions were 
made for the continuous recording of the ampli- 
tudes of the echo and jammer signals. In this 
manner, the jamming power required was meas- 
ured as a function of echo field strength. The 
use of various types of jamming signals veri- 
fied the laboratory results. 

In order to estimate the jamming power that 
would be required in the case of real ship tar- 
gets, the echo amplitudes were measured for 


several naval vessels. By comparing these meas- 
urements with those made on the corner reflec- 
tor it was possible to assign jamming power 
requirements to each vessel. It was concluded 
that a jamming power of 100 w might be re- 
quired in the case of the largest vessel, as- 
suming that a simple half-wave antenna was 
used for the jammer. 


9 5 RADIO-PRINTING SYSTEMS 

Studies were made on a variety of types of 
printing systems, to determine and improve 
their AJ characteristics. On the basis of the re- 
sults of these investigations, improved systems 
were developed which were sufficiently good 
from the AJ standpoint to be used as substi- 
tutes for voice or code systems, when the latter 
became jammed to such an extent as to be use- 
less. 


AJ Characteristics of Teleprinters 

A research project was established to investi- 
gate the AJ characteristics of five- and seven- 
unit printing telegraph systems and to devise 
means to improve their performance when 
jammed.^^ Susceptibility tests were run on two 
basic systems; namely, the five-unit start-stop 
teletype system and the synchronous seven-unit 
RCA error- detecting system. Four types of 
noise were utilized: (1) sawtooth impulses; (2) 
square-wave impulses ; (3) random keyed tones ; 
and (4) fluctuation noise. 

It was found that the last was the least effec- 
tive for jamming on all systems. Square-wave 
impulses were the most effective against a d-c 
signal, and a square wave keyed audio tone 
was the best against tone signals when the 
interference tone frequency differed from the 
signal tone by the keying rate. The most satis- 
factory circuit arrangement for combating 
jamming conditions includes: (1) space-diver- 
sity reception; (2) two-tone f-m keying; and 
(3) seven-unit operation employing synchro- 
nous transmission, with front-end correction 
and collation. 

Against fluctuation noise, a two-tone five-unit 


198 


NONRADAR ANTIJAMMING TECHNIQUES 


start-stop teletype system combined with space 
diversity has a 26-db signal-to-noise improve- 
ment over an on-off keyed single-receiver ampli- 
fier-rectifier five-unit start-stop teletype system. 
Synchronous regeneration will add 5.5-db im- 
provement. If the five-unit start-stop printers 
are replaced by seven-unit radio printers with 
collation, an additional 1.5 db can be realized. 


9.5.2 Impulse and Time Code Systems 

An investigation was made of the AJ char- 
acteristics of the British Beechnut system. The 
results led to the development of an improved 
system of the same type known as Voflag. 

Vulnerability of Beechnut 

Beechnut was a ground-to-aircraft communi- 
cation system employing two-tone keying to set 
up a message before the pilot on a display which 
consisted of six ideograms. The British Beech- 
nut equipment used two superaudible frequen- 
cies. 

Jamming tests were made on a complete 
Beechnut system, including the standard r-f 
transmitting and receiving equipment used for 
ground-to-aircraft operations.^® The interfer- 
ence was introduced at the receiver input. It was 
found that this system was jammed effectively 
by interference with one-half the amplitude of 
the desired carrier, if the jamming carrier was 
100 per cent modulated by a superaudible tone 
approximately equal to the frequency of the 
transmitted '‘marking” tone.^®® A similar type 
of interfering signal jammed the aircraft-to- 
ground acknowledgment signal when the inter- 
fering carrier was only one-tenth of the desired 
signal. 

Development of Voflag 

In order to overcome some of these difficul- 
ties, a two-tone system using a six-element 
error-proof code of well-known characteristics 
was developed. This system was known as 
Voflag. It was found that the Voflag system 
could be jammed effectively by a jamming 
carrier of one-half the intensity of the desired 
carrier if it was 100 per cent modulated by an 
audio tone approximately equal to the frequency 


of the transmitted marking or “spacing” tone. 
The error-proof code, however, was so arranged 
that an automatic answer-back was provided 
from the aircraft to the base station indicating 
“message O.K.” or “received with errors.” 
Manual acknowledgment was also provided for 
use when the pilot had carried out instruc- 
tions.^i^ Another version of Voflag printed the 
ideograms on a record slip instead of displaying 
them before a pilot. 

At the end of World War II, no units had 
been delivered, nor had the design of the printer 
attachment been completed. These jobs were 
finished, however, before work on the develop- 
ment ceased. 


9.5.3 Attachment 

A research project was established with the 
aim of protecting radio communications equip- 
ment against jamming by means of an auxiliary 
apparatus, which could be added to existing 
voice sets without modifying them, and which 
could be operated by unskilled personnel. 

Equipment Developed 

An airborne equipment weighing 41 lb was 
evolved, which consisted of a typewriter-like 
keyboard for sending, together with a tape 
printer for receiving. The operating speed was 
fixed at ten words per minute. This slow-speed 
radio printer could receive messages through 
noise-modulated interference 11 db stronger 
than the wanted signal. This J/S ratio was an 
improvement over voice communication by 
about 14 db; that is, about 25 times the jam- 
ming power was required to jam the printer as 
was needed to jam voice.^®^*^®® 

Basic Method. The printer signal consisted 
of a-f tones, which were introduced into the 
microphone jack of the voice transmitter. At 
the receiver, the signal was taken from the ear- 
phone jack. Because of the slow speed of opera- 
tion (ten words per minute) the bandwidth 
required for the printer-signal tones was quite 
narrow, about 20 c. During jamming the audio 
output of the receiver contained additional fre- 
quency components, whose energies were gen- 
erally spread over a much wider audio band- 


RADIO-PRINTING SYSTEMS 


199 


width. Consequently, when the desired printer- 
signal tones were selected by means of narrow- 
band audio filters, much of the jamming energy 
was eliminated. This method was the only one 
which was considered to be capable of protect- 
ing voice radio systems against jamming with- 
out modification of the existing equipment. 

On the other hand, the method was quite 
vulnerable to jammer modulation consisting of 
audio tones of the proper frequencies, or to 
jamming by captured equipment. In conse- 
quence, the printer-signal tones had to be 
scrambled prior to transmission and unscram- 
bled in the receiver. The enemy would thereby 
be forced to spread his jamming energy over a 
greater bandwidth, with a corresponding reduc- 
tion in effectiveness. The synchronization and 
phasing of the frequency scrambling-descram- 
bling operation requires a certain degree of 
skill; provision was made, therefore, to switch 
this feature out of operation when necessary. 

Effectiveness of Method 

When a jamming signal consists of modula- 
tion which is uniformly distributed over a given 
frequency bandwidth, the energy in any portion 
of that bandwidth is directly proportional to 
the width of the portion under consideration. 
If the signaling speed is reduced, therefore, and 
the audio bandwidth is decreased proportion- 
ally, the effective power of the interference is 
likewise reduced in direct proportion. This re- 
lationship holds on either an a-f or an r-f basis, 
depending on whether the selective circuits are 
in the audio or the r-f stages. 

In this development, inasmuch as 20-c r-f 
selectivity could not be obtained without drastic 
modification of the existing voice sets, it was 
necessary to utilize a-f selectivity, but over a 
relatively wide-band r-f link. It was found that 
under these conditions the strong jamming 
carrier interfered with the normal demodula- 
tion of the desired signal sidebands, as a result 
of which the wanted signal was appreciably 
suppressed in the audio output of the receiver. 
A study of this “apparent demodulation” phe- 
nomenon was made^®® and moderate success was 
achieved in the minimizing of its severity. 

An approximate rule is that when a-f selec- 
tivity is used on a signal which is transmitted 


over an r-f link subjected to jamming, the 
minimum effective r-f J/S power ratio varies 
inversely as the two-thirds root of the audio 
bandwidth. In other words, if the signaling 
speed be reduced, say, from 80 to 10 words per 
minute (and the audio bandwidth in propor- 
tion) , it becomes possible to operate through in- 
terference whose power is four times as great 
as formerly. This example makes it clear that 
still further antijamming protection could be 
achieved only at the expense of very low signal- 
ing speeds. Accordingly, 10 words per minute 
was selected as a practical minimum speed. 

Details of Printer 

Since the printer was expected to operate 
through conditions of jamming, special precau- 
tions were taken to insure satisfactory opera- 
tion during normally marginal conditions. 

Protection against fading was achieved by 
the frequency-shift system of mark-space key- 
ing, in which one audio tone was transmitted 
for marking, and another audio tone was trans- 
mitted for spacing; this gave very satisfactory 
results. A single-case printer was employed, be- 
cause of the risk that temporarily successful 
jamming might leave the printer in the wrong 
case. An error-protected printer code was em- 
ployed, so that, should the jamming manage to 
mutilate the signal, an error symbol would be 
printed in lieu of an erroneous character. This 
protection greatly improved the reliability of 
the printer, since mutilations were apparent at 
a glance and the mental effort of inspecting the 
test and correlating it with the confirmation 
was eliminated. 

Although a stop-short printer would have 
been preferred, it was not used because momen- 
tary jamming could then throw the printer out 
of step for quite a number of characters. The 
printer was therefore designed for synchronous 
operation; for this purpose a special tuning 
fork was employed, with a frequency stability 
of about one part in a million over a wide tem- 
perature range. This fork was sealed in a partial 
vacuum so that its rate would be unaffected by 
the low atmospheric pressures encountered at 
high altitudes. A special synchronous motor was 
developed, which provided the required power at 
a very low cost of size, weight, and power con- 


200 


NONRADAR ANTIJAMMING TECHNIQUES 


sumption. The synchronous operation was ap- 
plied to advantage to obtain optimum regenera- 
tion of the received signal and to synchronize 
the scrambling-descrambling operation. 

Many functions of the printer were per- 
formed electronically, rather than mechanically, 
and the resulting mechanical simplification is 
such that little tool-up time should be required 
for production of the printer. The printing-head 
and keyboard were designed as a compact unit, 
which could be located in the aircraft cockpit 
and connected to the main control unit by inter- 
connecting cables. 

The above features contributed to an in- 
herent operational simplicity and reliability 
suited to the type of military service for which 
the printer was designed. At the same time, 
two basically different types of secrecy were 
provided, and a third form could be added at 
very little cost, so that the printer is as much 
a secrecy device as it is an AJ attachment. 

Recommendations 

The equipment developed on this project is 
about the best solution foreseen for applications 


where the given limitations still apply. It could 
be added to any voice system at any time ; and, 
by its addition to a-m or pulse-modulated voice 
systems, the communication link would be en- 
abled to operate through stronger jamming, to 
about the same extent as could be accomplished 
by using c-w operation with highly trained 
telegraphists for the purpose. It is conceivable 
that this equipment, used with voice transmit- 
ters, might be considered as a satisfactory sub- 
stitute for c-w telegraphy. 

It is believed, however, that any peacetime 
program to achieve protection against jamming 
should not be concerned with the type of equip- 
ment already in service, but should be permitted 
an unrestricted field of development. Speed of 
communication should not have to be sacrificed 
in order to achieve AJ protection. Printers 
(when used) should function at high speed, 
with skilled keyboard operators. Preferably, 
however, voice communication should be used, 
allowing for speed without skilled operators. 
Possible methods for achieving these results 
include r-f carrier frequency scrambling and 
time modulation of pulses with time scrambling. 


PART IV 


RADAR APPLICATIONS 


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Chapter 10 


RECEIVING AND DIRECTION-FINDING EQUIPMENT FOR RADAR 

COUNTERMEASURES 


10.1 INTRODUCTION 

T he need for search and direction-finding 
[DF] facilities has been discussed in a 
general way in Chapter 1. The detailed discus- 
sion of such devices can be subdivided into a 
consideration of the design requirements of 
such equipment, the fundamental technique de- 
velopments necessary for the realization of 
these design requirements, and finally a descrip- 
tion of the various receivers, direction-finding 
equipments, and associated devices which have 
been found necessary for an effective radio 
countermeasures [RCM] program. All of the 
important technique developments which grew 
out of this program are covered in detail in the 
accompanying monograph,®^® so this chapter is 
devoted to a consideration of the design require- 
ments and a description of the equipments actu- 
ally developed for military use. 

The majority of this work was done by the 
Radio Research Laboratory (under contract 
OEMsr-411). Some of the early work was done, 
however, by the Columbia Broadcasting System 
(under contract OEMsr-867). There was also a 
considerable amount of activity in this field, of 
course, by various Service laboratories (espe- 
cially in connection with the development of 
pulse analyzers and other indicating equip- 
ment) and by the several manufacturers who 
did production engineering on these devices. 


2 DESIGN CONSIDERATIONS 

The myriad tasks which RCM receiving and 
DF equipments are called upon to perform de- 
mand either a single relatively complex and 
complete equipment, a basic equipment with a 
considerable number of attachments, or a col- 
lection of simple equipments, each of which per- 
forms a relatively small number of jobs. All 
three of the above solutions to the overall prob- 
lem have been tried, and all are successful. The 


choice under a given set of conditions must be 
made on the basis of a careful analysis of the 
problem at hand. The following general con- 
siderations concerning each of the principal 
functions of such equipment may be of aid in 
understanding the reasons for the specific de- 
signs discussed later in this chapter. 


10.2.1 Analysis of Enemy Radar by Use of 
Search Receivers 

Search receivers, when supplemented by suit- 
able indicating and analyzing devices, can be 
instrumental in obtaining much valuable in- 
formation concerning enemy radar equipment. 
Some of the operating characteristics that may 
be determined by searching, the reason for 
their importance from a countermeasures view- 
point, and the probable range of values that will 
be encountered are as follows : 

1. Carrier frequency (about 50 me and 
higher). In order to permit intelligent design 
and successful employment of countermeasures 
devices, it is important to know the exact oper- 
ating frequency of specific radar systems and 
the band of frequencies over which the radar 
sets of a given type are spread. 

2. Antenna polarization (horizontal, vertical, 
or rotating). Since it is important that the 
transmitter power available for jamming pur- 
poses be used as effectively as possible and since 
the maximum possible sensitivity is generally 
desired in receivers, it is essential that the 
polarization of the enemy emissions be ascer- 
tained and the jamming transmitter and search, 
warning, or DF receiver antennas be arranged 
accordingly. 

3. Lohe-sivitching rate (from about 1/2 to 
500 per second). An accurate knowledge of the 
lobe switching (or split rate) of enemy systems 
is of importance in the design and application 
of certain types of deception devices, for ex- 
ample, Peter. More detailed information is given 


203 


204 


EQUIPMENT FOR RADAR COUNTERMEASURES 


in Chapter 12. This can be readily determined 
where lobe switching of the radar transmitter 
is practiced. 

4. Maximum range (from a small fraction 
to hundreds of miles) . The maximum range for 
which a radar system is designed may be esti- 
mated from a knowledge of the pulse-repetition 
frequency (prf ranges from about 20 to 5,000 
pulses per second). In the case of an oscillating 
or rotating searching beam the actual maximum 
range may be ascertained for a specific target 
when the beam stops searching and locks on 
the target. Knowing the maximum range of a 
radar is important, since, in general, it is not 
desirable to operate jamming transmitters until 
they come within range of the radar system. 

5. Minimum range (from tens of yards to 
a few miles). The minimum design range may 
be estimated from a knowledge of the pulse 
length (from about 0.1 to 25 psec) and the 
pulse shape. Information as to the minimum 
range of an enemy radar system is not of par- 
ticular interest from an electronic countermeas- 
ures viewpoint but it may be of considerable 
value to other operational branches of the 
Armed Services and to the designers of our 
radar equipment. Information concerning the 
pulse shape, however, is of importance in the 
design of certain deception devices (see Chap- 
ter 12). 

6. Equivalent radiated power. Field inten- 
sity measurements, coupled with information 
as to the distance from the radar at which the 
measurements were taken, will permit an ac- 
curate estimate to be made of the equivalent 
radiated power of the radar and of the neces- 
sary sensitivity of warning receivers. 

7. Rate of rotation (from about 0.1 to 100 
per minute) . The probable rate of rotation of a 
radar is of considerable interest in the design 
and application of automatic search receivers 
since it influences the selection of the rate at 
which the receiver scans the frequency spec- 
trum. Furthermore, observations made on the 
rate of rotation are useful in determining 
whether a plan-position indicator [PPI] is used 
by the radar under surveillance. 

8. Resolution or directivity. Information 
concerning the directivity patterns in the hori- 
zontal and vertical planes will indicate the 


resolution or directivity of the radar and pro- 
vide an estimate of the antenna gain. Informa- 
tion about the vertical pattern may also reveal 
nulls or blind spots which may be used to ad- 
vantage in approaching the radar in question. 

10.2.2 4naly2:ing and Indicating Equipment 

It is evident from the foregoing that, in addi- 
tion to the search receiver itself, there is need 
for various associated analyzing, recording, and 
indicating equipment if full advantage is to be 
taken of the emission from a radar system in 
obtaining information relative to its operating 
characteristics. The auxiliary equipment in- 
cludes frequency meters, pulse analyzers, cath- 
ode-ray oscilloscopes, and audio oscillators. 

The accuracy of frequency meters for the 
radar portion of the frequency spectrum is, in 
general, not sufficiently great to permit the 
setting of jamming transmitters by reference 
to the stated absolute frequency. It is preferable 
to set such transmitters on frequency by em- 
ploying the same frequency meter as was used 
originally to determine the enemy radar fre- 
quency. Although the absolute calibration of 
such instruments may not be so accurate as 
desirable, their stability and relative calibration 
may be satisfactory if they are used first to 
determine the frequency to be jammed and 
then to set the jammer to this frequency. 

Spot- jamming operations (see Chapter 11) 
demand a high degree of accuracy in setting 
jamming transmitters on frequency. The most 
practical method of doing this has been found 
to be the simultaneous reception of the signals 
of the radar to be jammed and of the jammer. 
This may be done aurally with any receiver with 
small enough bandwidth, sufficient dynamic 
range, and satisfactory discrimination against 
spurious signals. It may also be done more con- 
veniently by using a receiver provided with 
panoramic presentation of signals. Provision of 
panoramic presentation may actually simplify 
the design of a receiver by making it easy to 
identify spurious signals, thus eliminating the 
necessity of designing the receiver so as to 
reject them. Panoramic presentation certainly 
makes the monitoring of the jammed signal 
easier, since the variations in signal strength. 


DESIGN CONSIDERATIONS 


205 


attempts at detuning, etc., may be observed im- 
mediately, both as to magnitude and direction. 
In general, panoramic presentation makes jam- 
mer frequency setting and monitoring easier 
and more accurate. Provision for panoramic 
presentation may be made as a part of the re- 
ceiver design or as an attachment for many 
types of standard search receivers. 

10.2.3 Automatic Search Receivers 

Radar reconnaissance, for reasons already 
mentioned, is frequently done from aircraft. 
The task is not particularly simple even though 
the geography may be such that the searching 
craft is able to stay out of range of the radar 
under investigation. For example, in an area 
where there is only one radar (or very few) 
operating on an unknown frequency, it is neces- 
sary that there be a double coincidence if the 
signal is to be heard ; that is, the search receiver 
must be tuned to the radar frequency at the in- 
stant the radar is oriented toward the search re- 
ceiver. 

Since radar and similar types of emissions 
(such as for radio-controlled glide bombs or 
tanks) may take place anywhere in a very wide 
band of frequencies, searching becomes a very 
tedious job if it is undertaken in a thorough 
manner. At low radar frequencies this is not so 
serious a problem as at high frequencies since, 
in the former case, the directivity of the radar 
transmitting antennas is not so great as at high 
frequencies. Furthermore, at low radar fre- 
quencies there are often spurious side lobes of 
radiation that emit sufficient power to permit 
reception on a sensitive receiver even though it 
may not be in the main beam of the radar. 

At high radar frequencies the search prob- 
lem is doubly difficult, since not only are the 
beams generally extremely sharp and possessed 
of only very minor spurious lobes, but also there 
is a much larger number of possible channels. 
On the other hand, if the reconnaissance is 
over an area where there are a large number of 
radars operating, it may be difficult, because of 
the speed of flight and the number of radars in- 
volved, to record and distinguish between all 
the radar signals heard. 

The various types of automatic tuning and 


recording means that have been devised to 
alleviate these difficulties are described on the 
following pages. In some instances, these de- 
vices are such that they can be carried on 
regular bombing missions (operating without 
attention) and thus provide preliminary data 
concerning enemy radar. In general, however, 
automatic devices do not record the operating 
frequency of received emissions with sufficient 
accuracy for the presetting of jamming trans- 
mitters. Rather, they are useful for indicating 
the general whereabouts, both in frequency and 
geographical location (by comparing the time 
of signal reception with the flight log), of the 
radar stations heard. A detailed search with 
more precise measuring equipment can then be 
made with the minimum amount of effort. 

Sensitivity of Radar Search 
Receivers 

It is not generally necessary that radar 
search receivers have the extreme sensitivity 
which is desirable in communications receivers 
or in receivers that are a part of a radar system. 
This is true because of the extremely high field 
intensities that exist at the search receiver 
location when it is within range of a radar. This 
fact is obvious when it is recalled that only a 
small portion of the total energy intercepted by 
the target is returned to the radar and yet this 
echo must be sufficiently great to permit the 
reception of a discernible signal by the radar 
receiver. The warning receiver, on the other 
hand, is exposed to the intense field that exists 
at its location whenever the radar beam is 
oriented in that direction. 

Sensitive radar search receivers are useful, 
however, since they will permit the reception 
of radar signals at maximum distances. Fur- 
thermore, with a sensitive receiver, radar emis- 
sions will be observable even though the radar 
involved may not be ‘booking’ ' directly toward 
the receiver. 

10.2.5 Radar Warning Receivers 

The desirability of knowing, under many cir- 
cumstances, when one is being observed by 
radar of a certain type led to a serious study 


206 


EQUIPMENT FOR RADAR COUNTERMEASURES 


of the possibility of using radar warning re- 
ceivers. Under some circumstances (e.g., sub- 
marine operations), it is feasible to use stand- 
ard search receivers for obtaining warning. 
This type of operation, although it has proved 
to be of the utmost importance, needs no further 
discussion. It is sometimes necessary, however, 
to develop special receivers for radar warning, 
especially if the receiver must operate unat- 
tended and give warning only when actual 
danger exists and proper evasive action or other 
measures must be taken. 

Although the basic idea of a radar warning 
receiver was that of a simple device, experience 
has shown that to be useful the receiver must 
be capable of rather complex operations. This 
was particularly true in the European Theater 
of Operations. In this area the enemy search- 
light-control [SLC], gun-laying [GL], and 
ground -controlled -interception [GCI] radar 
were all in a narrow band of frequencies and 
enemy aircraft-interception [AI] and coastal- 
watch equipment were similarly disposed in ad- 
jacent bands. To be of maximum usefulness, a 
warning receiver has to be able to discriminate 
between these different types of radar, since 
different evasive tactics are practiced against 
the various types. 

The time that may elapse before evasive 
action must be undertaken is different for vari- 
out types of radar. For example, evasive action 
against GL need not be taken until after the 
enemy radar has been centered exactly on the 
target for a period long enough to supply suffi- 
cient data to the antiaircraft predictors to per- 
mit accurate firing. Thus, GL warning devices 
might include means for determining when this 
centering takes place and in addition introduce 
a time delay of something less than a minute 
(since all predictors require a flow of uninter- 
rupted information for a certain period of time) 
before giving a warning signal. 

In the case of GCI, a warning need not be 
given until the target has been under sur- 
veillance for 5 min or thereabouts. For AI warn- 
ing, however, the warning signal should be 
given whenever the Al-equipped aircraft is 
almost close enough to press home the attack. 
Unless arrangements are made to provide these 
distinguishing features, the warning equip- 


ment, at least in a congested area, will give 
almost continual warnings which, if heeded, 
would result in an intolerable amount of evasive 
action. 

Warning receivers for the early-warning 
[EW] radar frequencies are not required, as a 
rule, since attacking aircraft must fly over the 
EW radars in any event. However, in theaters 
where the location of every EW equipment has 
not been ascertained by prior search — i.e., in 
initial raids into new territory — the use of 
warning receivers for the EW bands may be 
useful in indicating when one first comes under 
scrutiny and when interception may be antici- 
pated. 

The above considerations resulted in the de- 
velopment of several radar warning receivers, 
but, because of the rapidly shifting tactical situ- 
ation and necessary delays encountered in plac- 
ing equipment of this kind into production, 
none of these received extensive operational 
use. The British, on the other hand, did manage 
fairly early in World War II to get one warning 
receiver (Boozer) into fairly widespread use. 
The effectiveness of such devices is difficult to 
ascertain, since a good part of their value may 
be due to their effect on the morale of the 
users, especially if they make it possible for 
the operators to relax except in times of actual 
danger. At any rate, the various developments 
of this type are described later in this chapter, 
so that the reader may evaluate for himself the 
usefulness of such devices under a given set of 
circumstances. 


10.2.6 Homing Systems 

By providing a search receiver with suitable 
directional antennas, switching mechanisms, 
and indicators, a system can be developed that 
will assist the craft carrying the equipment 
to orient itself toward a source of radio, radar, 
or jamming signals. An installation of this type 
is known as a homing system, since it will indi- 
cate the course to be taken in order ultimately** 
to reach the source of signals. The use of equip- 
ment of this kind is more or less confined to 

» Because of drift, a spiral course will actually be 
followed unless corrections are made. 


EQUIPMENT DEVELOPMENTS 


207 


airplanes since in larger, slower moving, and 
less mobile craft the use of DF systems offers 
several advantages that more than offset their 
added size and complexity. Direction-finding 
systems are also applicable to aircraft. They 
bear a relation to homing systems similar to 
that which the turret guns bear to the fixed 
guns on the airplane. With a homing system 
or with fixed guns the airplane must be turned 
toward the target, whereas with a DF system 
or with turret guns the airplane may fly a 
chosen course while still coming to bear upon 
the target. 

Homing systems are most useful to airplanes 
or guided missiles that wish to attack a source 
of signals. For example, they can be of con- 
siderable assistance to low-flying aircraft intent 
upon attacking an enemy radar station. 
Although the location may be precisely known, 
when the plane is flying at low altitude it will 
seldom be possible to see the station until the 
aircraft is almost over it. Homing equipment 
should assist materially in keeping the aircraft 
headed toward the target. 

Another application is the locating of air- 
borne jammers or of radar-carrying aircraft 
for the purpose of attack. In this application, 
homing methods have the advantages over 
AI radar that they require less elaborate equip- 
ment and that they do not provide any radio 
warning to the enemy, even if he is equipped 
with warning receivers. 

In the selection of homing equipment for a 
specific application it is exceedingly important 
to bear in mind the need for using an antenna 
system whose polarization corresponds to that 
of the transmitter. Thus, if the source of signals 
is an antenna having vertical radiating ele- 
ments, a vertically polarized antenna should be 
used for the homing system if erroneous results 
are to be avoided. It should also be noted that 
most directional antenna systems operate 
properly only over a limited band of frequen- 
cies, since the problem of providing a broad- 
band directional system is a very difficult one. 

Homing equipment has not been found to be 
of any great practical value for radio and radar 
reconnaissance undertaken for the purpose of 
locating enemy installations. In operations of 
this type, it is necessary to turn the homing- 


equipped craft toward the target in order to 
determine its bearing and to repeat this opera- 
tion from two or more locations. With aircraft 
this procedure causes the reconnaissance plane 
rapidly to approach dangerously close to the 
enemy installations. Furthermore, it is time- 
consuming because of the need for orienting 
the craft, first one way and then the other, to 
make certain it is on the correct heading. This 
operation often results in considerable doubt 
concerning the result, particularly if the radar 
signal is waxing and waning as it scans back 
and forth. Thus the use of homing systems for 
spotting the locations of enemy installations, 
while possible, cannot be recommended. The 
use of a DF system is preferable for this 
purpose. 


10.2.7 Direction-Finding Systems 

A radio DF system differs from a homing 
system in that the direction from which a 
signal is arriving may be determined directly 
from the indications of the direction finder. 
Equipment of this type is useful not only in 
aircraft but also in ground and sea-borne 
craft or in fixed ground-based installations. 

With a radio direction finder the direction 
toward a source of signals (radio, radar, or 
jamming) may be ascertained without requir- 
ing the vehicle carrying the equipment to 
deviate from a prescribed course. Direction- 
finding equipment, while more complicated than 
homing equipment, does not necessarily require 
more skill for its operation; the reverse may, 
in fact, be true in some instances. 

As with homing equipment, the polarization 
of the antenna of a direction finder should be 
the same as that of the transmitter antenna. 
In the more elaborate systems, provisions are 
made to obtain proper response from vertically, 
horizontally, and circularly polarized waves. 

3 EQUIPMENT DEVELOPMENTS 

Most of the receiving and DF equipment 
developed by Division 15 for radar intercept 
employed more or less standard designs. 


208 


EQUIPMENT FOR RADAR COUNTERMEASURES 


although the techniques used^^® to achieve the 
desired results were somewhat novel. In other 
words, the receivers employed either standard 
superheterodyne circuits or in some cases used 
direct-detection circuits with crystal detectors. 
The design of the various mixers, oscillators, 
preselectors, i-f amplifiers, etc., for the re- 
ceivers, however, involved radical departures 
from the conventional type of design because 
of the higher frequencies involved and the 
larger frequency coverages obtained. Since the 
various technique developments have been dis- 
cussed elsewhere,®^^ this section will be devoted 
to comments concerning unusual features of the 
receiving and DF equipments listed in Tables 
1 and 2. 

^ ^ Search Receivers 

Most of the search receivers shown in Table 
1 employ standard superheterodyne circuits. 
Because of the very high frequencies involved, 
r-f amplification before the mixer is not 
employed, since the amplifiers available at the 
time of the development of the receivers did 
not allow an improvement of signal-to-noise 
ratio by this means. Some of the receivers, 
however, do employ selective circuits before 
the mixer to eliminate image and harmonic 
responses. The mixers employed are diodes for 
frequencies below a few hundred megacycles 
and crystals for the higher frequencies. The 
i-f amplifiers are generally very wide band ( 10 
to 20 me) to improve the probability of inter- 
cepting sweeping signals. Most of these re- 
ceivers are equipped with video output channels 
(for use in conjunction with pulse analyzers 
and other similar equipments) and panoramic 
adapter outputs in addition to regular aural 
output. Some of the receivers include provisions 
for narrowing the i-f amplifier bandwidth to 
allow use of the receiver for setting jammers 
to frequency. A general design feature of most 
of the receivers is the provision of inter- 
changeable tuning units for various frequency 
ranges. These tuning units contain preselection 
filters, the local oscillator, the mixer, and some- 
times one or more stages of i-f amplification, 
while the remainder of the receiver contains 
all the other circuits. 


It will be noted that two direct-detection 
receivers are listed. In view of the comments 
in Section 10.2.4 it will be seen that these 
receivers can be quite useful for most radar 
intercept work, since the signal strength en- 
countered is generally quite high. One of these 
receivers employs a rather novel presentation 
system (including a tape and a panoramic dial) 
described elsewhere.®^^ 

One receiving system which incorporates 
virtually all of the best design features avail- 
able to date (Type D-9000) will be described 
as an example of the type of equipment de- 
veloped. The receiving equipment (see block 
diagram in Figure 1) consists basically of 
antennas for three functions, the several units 
of the receiver which were mounted in a single 
receiver console, and a Type DBM-1 direction- 
finding unit. 

As shown in the diagram, each antenna is 
connected to the receiver through an antenna 
and video switching unit. The r-f switches in 
this unit are operated by remote control and 
select specific antennas to be connected to each 
of the two separate receiving channels. This 
feature permits operation of one receiver as 
a monitor while searching is being done with 
the other receiver. 

The receiver uses a standard superhetero- 
dyne circuit. The preselector and mixer, 
together with the first few stages of i-f 
amplification, are housed in the tuning unit, 
while the remainder of the circuits are housed 
in the presentation unit. This presentation unit 
consists of an i-f amplifier (for further amplifi- 
cation of the 200-mc i-f signal from the 
tuning unit), a detector, a video amplifier, a 
panoramic-presentation unit (which operates 
by sweeping a narrow-band receiver across 
the i-f amplifier output), and a pulse-analysis 
unit. The pulse-analysis unit indicates on 
meters the prf and the pulse width of the 
received signal. In addition, video output from 
both presentation units is fed into the switching 
unit, which provides selection of circuits to 
feed video signals either to the DBM-1 indi- 
cator, for determination of the direction of the 
signal source, or to the remote panoramascope 
mounted on the transmitter console of an 
Elephant jamming system (see Chapter 11), 


EQUIPMENT DEVELOPMENTS 


209 



Table 1. 

Radar countermeasures receiving equipment. 



Identification 

Nos. 

Use 

Frequency References 

range (me) Keierences 

Remarks 



Army: SCR-587 
Navy: ARC-1 

Superheterodyne search 
receiver. 

See tuning 
units below. 

425 

Early model receiver superseded 
by those listed below. 

RRL: D-1003 

Div. 15: RP-144 
Army /Navy: 
AN/APR-1 

Airborne superhetero- 
dyne search receiver. 

See tuning 
units below. 

650 

I-f bandwidth 2 me. 

RRL: D-1003 

Div. 15: RP-144 
Navy: AN/SPR-1 

Ship-borne superhetero- 
dyne search receiver. 

See tuning 
units below. 


Above receiver converted for 
shipboard use. 

RRL: D-1005 

Div. 15: RP-144 
Army/ Navy : 
AN/APR-4 

Airborne superhetero- 
dyne search receiver. 

See tuning 
units below. 


I-f bandwidth switch: 4 or V 2 me. 

Army: TU-58A 

Navy: CPR-47-AAF 

Tuning unit for above 
receivers. 

100-370 

426, 436 

Early model; two-dial control. 

Army: TU-57A 

Navy: CPR-47-AAF 

Tuning unit for above 
receivers. 

290-950 

426, 436 

Early model; two-dial control. 

RRL: D-104 

Div. 15: RP-141 
Army: TU-56A 
Army/ Navy : 
TN-l/APR-1 
TN-16/APR-4 

Tuning units for above 
receivers. 

40-105 

512 

Available with single-dial control 
and either manual, motor- 
driven, or sector-sweep opera- 
tion. 

RRL: D-101 

Div. 15: RP-141 
Army: TU-58B 
Army/ Navy : 
TN-2/APR-1 
TN-17/APR-4 

Tuning units for above 
receivers. 

75-300 

494, 501 

Available with single-dial control 
and either manual, motor- 
driven, or sector-sweep opera- 
tion. 

RRL: D-102 

Div. 15: RP-141 
Army: TU-57B 

Army/ Navy : 
TN-3/APR-1 
TN-18/APR-4 

Tuning units for above 
receivers. 

300-1,000 

494, 513 

Available with single-dial control 
and either manual, motor- 
driven, or sector-sweep opera- 
tion. 

RRL: D-103 

Div. 15: RP-141 
Army: TU-59B 
Army/Navy : 

TN-3/ APR-1 
TN-19/APR-4 

Tuning units for above 
receivers. 

950-3,300 


Manual tuning, two-dial control. 

RRL: D-1500 

Div. 15: RP-212 
Army/ Navy : 
TN-27/APR 

Tuning units for above 
receivers. 

1,000-3,100 

397 

Single-dial control. 

RRL: RA-2600 

Div. 15: RP-135 

Army /Navy : 
AN/APR-5 

Airborne superhetero- 
dyne search receiver. 

1,000-3,100 

489, 536 

AN/APR-5A is same as 
AN /APR-5 except that mixer 
may be changed to cover 3,000 
to 6,000 me. 

RRL: RA-2700 

Div. 15: RP-291 
Army/Navy : 
AN/APR-6 
AN/APR-5A 

Airborne superhetero- 
dyne search receiver. 

3,000-6,000 

536, 641, 
664 

Can be used with R-1000 variable 
high-pass filter (see Chapter 4) 
for identification of spurious 
responses. 


210 EQUIPMENT FOR RADAR COUNTERMEASURES 


Table 2. Radar countermeasures homing and direction-finding equipment. 

Identification 

Nos. 

Use 

Frequency 
range (me) 

References 

Remarks 

RRL: C-1700 

Div. 15: RP-106 

Antenna and video com- 
mutator for homing. 

40-3,000 

526 


RRL: C-1900 

Div. 15: RP-209 

Antenna and video com- 
mutator and indicator 
for homing. 

Dependent on 
receiver. 

671, 695 

Available with either electronic 
or mechanical commutation. 
Antennas for horizontal polar- 
ization for azimuth only; hom- 
ing for 100- to 200-mc range 
also available. 

RRL: M-3900 

Div. 15: RP-242 

Antenna relay plus A-N 
cam for homing. 

Up to 1,000 

426 


RRL: C-1600 

Div. 15: RP-188 
Army/Navy: 
AN/APQ-14 

Homing receiver. 

90-130 


For use with Pelican or Dragon 
vehicle as homing bomb. 

RRL: C-2100 

Div. 15: RP-298 
Army/Navy: 
AN/APA-42 
AN/APA-24 

Airborne direction-find- 
ing system. 

100-165 

165-275 

275-450 

450-750 

411, 658 

Uses Adcock antenna for vertical 
polarization and dipole for hori- 
zontal polarization, mounted as 
single unit. Heads for various 
ranges mentioned are inter- 
changeable on most models on 
single mount. Some of these 
units have hydraulic drive; 
others electric drive. Dipole and 
special converter also available 
for use on horizontal polariza- 
tion only for range 50 to 100 
me. 

RRL: M-2300 

M-3000 

Div. 15: RP-298 
Army/ Navy : 
AN/APA-17 

Airborne direction-find- 
ing system. 

300-1,000 

394, 636 

Employs constantly rotating an- 
tenna assembly with polar 
indication. 

RRL: M-2600 

Div. 15: RP-271 
Navy: CXGA 

Ship-borne direction- 
finding system. 

300-900 

607, 636 

Early model ship-borne direction- 
finding system replaced by re- 
vised model listed below. 

RRL: M-4100 

Div. 15: RP-271 
Navy: DBM-1 

Ship-borne direction- 
finding system. 

300-1,000 

603, 636 

Revised ship-borne direction- 
finding system. Similar to 
AN/APA-17 electrically. 

RRL: M-6200 

Div. 15: RP-298 
Army/Navy: 
AS-222/APA-17 

Airborne direction-find- 
ing head. 

65-280 

828 

For use on horizontal polarization 
only with above direction-find- 
ing systems. 

RRL: M-6100 

Div. 15: RP-271 

Revised ship-borne di- 
rection-finding head. 

90-1,400 

731 

For use with above direction- 
finding systems. 

RRL: M-6400 

Div. 15: RP-298 
Army/ Navy : 
AS-108B/APA-17 

Revised airborne direc- 
tion-finding head. 

135-2,100 

829 

Scaled-down model of above head 
for airborne use. 

RRL: M-4500 

Div. 15: RP-271 
Army/Navy : 
AS-186/APA-17 

Airborne or ship-borne 
direction-finding head. 

1,000-3,500 

382, 636, 
661 

For use with above direction- 
finding systems. 


EQUIPMENT DEVELOPMENTS 


211 


Identification 

Nos. 


Use 


Table 2. {Continued) 


Frequency 
range (me) 


References 


Remarks 


RRL: C-1100 

Div. 15: RP-139 
Army/ Navy : 
AN/APR-2 

Direct-detection search 
receiver. 

90-300 

300-1,000 

RRL: D-2100 

Div. 15: RP-408 
Army/ Navy : 
AN/APA-7 

Direct-detection search 
receiver. 

1,000-3,500 

RRL: K-2000 

Div. 15: RP-435 

Army /Navy: 

AN /APR-9 

Airborne superhetero- 
dyne search receiver. 

See tuning 
units below. 

RRL: K-2100 

Div. 15: RP-435 

Army /Navy: Part of 
AN/APR-9 

Tuning unit for above 
receiver. 

2,000-4,000 

RRL: Q-2100 

Div. 15: RP-435 

Army /Navy: Part of 
AN/APR-9 

Tuning unit for above 
receiver. 

6,670-10,900 

RRL: D-9000 

Div. 15: RP-462 
Navy: Part of XMBT 

Receiving system for 
XMBT jamming sys- 
tem. 

See tuning 
units below. 


509, 634 Provided with mechanical pano- 
ramic indicator and tape re- 
cording. 

826 


Includes 200-mc center frequency 
i-f amplifier and other pro- 
visions for eliminating spurious 
responses. Also includes pano- 
ramic-presentation unit. 


Consists of two separate receiving 
channels, each similar electri- 
cally to AN/APR-9 receiver 
above, plus additional control 
and indicating features. 


RRL: D-9010 
Div. 15: RP-462 
Navy: Part of XMBT 

RRL: M-6700 
M-6600 

Div. 15: RP-271 

RRL: M-7100 
Div. 15: RP-271 


Tuning unit for above 
receiver. 


Airborne or ship-borne 
direction-finding head. 


Submarine direction- 
finding system. 


2,000-4,000 


5,000-12,000 


2,300-4,600 


741 For use with above direction- 
finding systems. 


RRL: D-9080 Tuning unit for above 6,670-10,900 

Div. 15: RP-462 receiver. 

Navy: Part of SMBT 


RRL: D-2800 
Div. 15: RP-462 


RRL: A-2100 
Div. 15: RP-147 
Army: RC-164B 


Unit ship-borne super- 
heterodyne search re- 
ceiver. 

Same as XMBT 
receiver 
above. 

Consists of single channel of 
above XMBT receiver. 

Direct-detection warn- 
ing receiver. 

65-130 

505, 548 Single-channel receiver covering 
frequency ranges given with 
separate r-f heads. 


RRL: R-800 Three-channel direct- 400-600 

Div. 15: RP-287 detection warning re- 

ceiver. 


RRL: Z-2000 
Div. 15: RP-112 
Army/Navy : 

AN /APR-3 


Two-channel direct- 480-500 

detection warning re- 510-600 

ceiver. 


368, 417 


Contains prf discrimination cir- 
cuits. 


212 EQUIPMENT FOR RADAR COUNTERMEASURES 


Table 2. {Continued) 

Identification 

Nos. 

Frequency 
range (me) 

References 

Remarks 

RRL: D-2200 

Div. 15: RP-425 
Army /Navy: 
AN/APA-41 

Panoramic adapter. 


Operates on 30-mc center i-f 
amplifier output from standard 
search receivers. 

RRL: R-1600 

Div. 15: RP-286 

Recorder for search re- 
ceivers. 


Early model superseded by unit 
listed below. 

RRL: D-1800 

Div. 15: RP-276 
Army /Navy: 
AN/APA-23 

Recorder for search re- 
ceivers. 

398, 676 

Operates with standard single- 
dial search receivers. 


so that the transmitter operator may observe 
the signal and set his transmitter accordingly. 

A pair of ordinary tilted-cone antennas (see 
Chapter 4) are provided for general search use. 
These are used to provide satisfactory coverage 
in all directions for both horizontal and vertical 
polarization. There are also provided four 


considerable discrimination against the trans- 
mitter antenna and considerable directivity in 
the direction from which the signal is being 
received. In addition, a standard Type DBM-1 
DF antenna and indicating unit are provided; 
these are used to determine the direction from 
which signals are received. 



Figure 1. Block diagram of receiving section of the Elephant ship-borne jamming system. 


horn-type antennas (monitoring antennas), 
which are mounted to '‘look” in four directions, 
so that each antenna covers a different quad- 
rant in azimuth. The purpose of these monitor- 
ing antennas is to pick up the enemy signal 
while the jamming transmitter is operating. 
These antennas accomplish this by having 


10.3.2 Attachments for Search Receivers 

The various attachments which have been 
developed by Division 15 for use with standard 
search receivers are of quite diverse types; 
they are also listed in Table 1. Since the tech- 
niques involved have been discussed else- 



EQUIPMENT DEVELOPMENTS 


213 


where,®®® no further comment concerning such 
devices appears necessary. 


10.3.3 Warning Receivers 

The method of operation of warning re- 
ceivers means that such receivers can be 
relatively insensitive and can generally be 
preset to the desired frequency. This means 
that the r-f circuits in such receivers can, in 
general, be quite simple. The presentation 
circuits, which are called upon to discriminate 
between various prPs and other features of 
radar signals, may be quite complex. The warn- 
ing receivers shown in Table 1 are all of the 


direct-detection type. They consist, in general, 
of r-f filters followed by crystal detectors and 
audio or video amplifiers, which deliver their 
output into various types of indicating systems. 
Some of the receivers include two or three r-f 
channels in order to give warning against 
various radar frequencies. 


10.3.4 Homing and Direction-Finding 
Systems 

The various homing and DF systems de- 
veloped by Division 15 are listed in Table 2. 
Since these systems have been described in 
detail elsewhere,®®® no further discussion is 
needed. 


Chapter 11 

RADAR JAMMING TRANSMITTERS 


111 INTRODUCTION 

R adar jamming transmitters played a very 
. important role in the radio countermeas- 
ures [RCM] program of World War II. They 
accounted for much of the success of the pro- 
gram (along with the use of confusion reflectors 
described in Chapter 12) and represented the 
largest single item of expenditure for the pro- 
gram. 

The discussion of radar jamming trans- 
mitters breaks itself naturally into a considera- 
tion of the design requirements of such equip- 
ment (which naturally depend to a large extent 
on the radar employed by the enemy), a dis- 
cussion of the fundamental technique develop- 
ments necessary for the realization of these 
design requirements, and Anally a description 
of the various transmitters and associated 
developments which were found necessary for 
an effective RCM program. All the important 
technique developments are covered in detail 
in the accompanying monograph.*^^^ This 
chapter is devoted to a consideration of the 
design requirements and a description of the 
transmitters actually developed for military 
use. 

The majority of this work was done by the 
Radio Research Laboratory under contract 
OEMsr-411. Some of the early work was done, 
however, by the Columbia Broadcasting System 
under contracts OEMsr-653 and OEMsr-867. 
The General Electric Company also did most 
of the development work on one transmitter 
described herein (Type TDY) under a Navy 
development contract. There was also a con- 
siderable amount of activity in this field, of 
course, by various Service laboratories and by 
the several manufacturers who did production 
engineering on these transmitters. 


” 2 general design CONSIDERATIONS 

Jamming transmitters are distinguished, 
among other things, by (1) the type of enemy 


equipment they are designed to nullify; (2) 
whether they are airborne, ship-borne, ground- 
based, or expendable; (3) whether they pro- 
vide barrage or spot jamming; and (4) their 
effective output power. For this reason a 
variety of jamming transmitters have been 
developed, each intended for specific applica- 
tions. There have even been more than one 
type of transmitter for a given frequency 
band, each differing from the others in one or 
more of the above respects. In many cases it 
was necessary to undertake the development of 
new tubes in order to provide means for gen- 
erating the required r-f energy. This latter 
work is covered in Chapter 3. 

As already mentioned, the success of any 
RCM activity depends to a great extent upon 
the skill with which the operation is planned 
and executed. Intelligent planning, however, 
requires a thorough knowledge of the virtues 
and shortcomings of available methods and 
equipment. Therefore, some of the more perti- 
nent factors that influence the use of jamming 
transmitters are discussed on the following 
pages. 


11.2.1 Enemy Radar Facilities 

Both the Germans and the Japanese were 
very active in radar development and use 
during World War II. The German radar facili- 
ties have been estimated to have been a two 
billion dollar investment. The Japanese radar 
system was less extensive but still represented 
a sizable portion of their war effort. 

Although the radar designs used by the 
enemy determined the frequency ranges, power 
output ranges, etc., which received the earliest 
and most concentrated attention, it was recog- 
nized from the beginning that information as 
to exactly the equipment or tactic the enemy 
would use next was very difficult to obtain and 
was always somewhat uncertain. This meant 
that, while a large amount of effort was neces- 
sarily devoted to immediate problems, a pro- 


214 


GENERAL DESIGN CONSIDERATIONS 


215 


gram was initiated to develop a series of jam- 
ming transmitters having a wide range of 
power output and other characteristics for 
covering the entire radar spectrum. Obviously, 
those transmitters covering the ranges in which 
enemy radar was found were manufactured and 
used in far larger quantities than the remainder 
of the series; however, the remainder of the 
series was of considerable insurance value. For 
the purposes of this book, which is concerned 
more with a presentation of the “state of the 
art’’ than with a historical treatment, these 
effects are mentioned only to enable the reader 
to understand the apparently uneven emphasis 
on various frequency ranges; those interested 
in details of the enemy equipment may find 
such information elsewhere.®^^ 


Communications versus Radar 
Jammers 

Transmitters intended for jamming com- 
munications channels differ in a number of 
respects from those intended for jamming 
radar channels. For example, communications 
jammers operate on lower frequencies than do 
radar jammers, the dividing line occurring at 
about 50 to 100 me. Also more power per 
receiver channel is generally required for com- 
munications jamming than for radar jamming. 
On the other hand, the communications channel 
is very narrow (a few cycles per second for 
some hand telegraph to a few thousand cycles 
per second for voice) as compared to the radar 
channel (fraction of a megacycle per second 
to a few megacycles per second). Finally, the 
type of modulation that may be excellent for 
distracting the communications operator may 
differ greatly from that which is most effective 
in obscuring the desired signals on a radar 
indicator. 

It is, in general, more difficult to jam a 
communications channel than a radar channel. 
One reason for the greater difficulty is the fact 
that the desired signal on the communications 
receiver is usually stronger than the echo signal 
received by the radar. A second reason is that 
communications channels, notably radiotele- 
graph channels, are very narrow. 


11.2.3 Airborne, Ship-Borne, Ground- 
Based, and Expendable Jammers 

Jamming by transmitters located on the 
ground requires a maximum amount of power, 
whereas expendable jammers require the mini- 
mum amount if they are sown, as intended, 
close to the communications or radar receivers 
that are to be jammed. This is fortunate, since 
ground-based equipment has the greatest 
amount of input power available, whereas 
expendable jammers have the least. Airborne 
jammers, on the other hand, are probably the 
most versatile, since they can reach the most 
receivers, can generally be carried by the air- 
craft to be protected, and can be flown over the 
scene of action. Thus, they can often accomplish 
the desired result with much less power than 
even the most advantageously located ground- 
based unit would require. However, in spite of 
the advantages of great mobility, relatively 
low power, etc., airborne equipment is not 
necessarily the best. 

As a practical matter, it may be best to 
confine airborne equipment to use against 
particular enemies of the aircraft and to use 
ground-based or mobile equipment against 
particular enemies of the ground forces. Indi- 
vidual exceptions to this general policy will, 
of course, be advisable. An example is the use 
of ground-based jammers against aircraft- 
interception [AI] radar and ground-controlled- 
interception [GCI] communications channels 
as already mentioned in Chapter 1. 

Ship-borne jammers, in general, resemble 
ground-based jammers more than they do air- 
borne jammers; however, several of the jam- 
mers originally intended for airborne use have 
been adapted to ship-borne installations by the 
addition of highly directive antenna systems. 
Considerations similar to the ones given above 
for airborne versus ground-based jammers 
apply to the relative value of airborne and 
ship-borne jammers for naval work. 

Expendable jammers, although they offer 
interesting possibilities, were not used very 
extensively. Expendable jammers may be of 
several types, such as parachute-borne (to jam 
during the period of descent), grounded (to 
jam from the ground), and floating (to screen 


216 


RADAR JAMMING TRANSMITTERS 


naval vessels). In general, jammers of this type 
will not be effective against systems having 
highly directive antennas unless the jammers 
are directly in the beams of the antennas. For 
this reason and others, expendable jammers 
for radar have not proved too practical. 


Barrage versus Spot Jamming 

The process of radiating jamming energy 
over a band of frequencies so as to be certain 
of blanketing the victim channel (either com- 
munications or radar) is known as barrage 
jamming. Contrasted to barrage jamming is 
spot jamming, in which the transmitter is tuned 
to exactly the same frequency as the victim 
signal. 

A barrage jammer, since it spreads the en- 
ergy over a large part of the frequency spec- 
trum, requires considerably more power for the 
same degree of effectiveness than does an ac- 
curately tuned spot jammer. Although with a 
given amount of power spot jamming is more 
effective than barrage jamming, the former re- 
quires the attendance of skilled operating per- 
sonnel. 

In the jamming of radar channels, the type 
of operation to be undertaken will influence, to 
a large extent, whether spot or barrage jam- 
ming is used. Spot jamming, for example, 
would probably be used with ground-based jam- 
mers operating against one or a few enemy 
radars. Under such circumstances, however, the 
need for skilled personnel is no handicap, since 
such personnel would probably be available any- 
way to maintain the jamming equipment. In 
airborne applications, however, the need for an 
operator and additional equipment may not be 
compatible with other requirements. Spot jam- 
ming is necessary, however, regardless of the 
extra personnel required and the extra com- 
plexity of the equipment involved, if the enemy 
radar sets are so dispersed in frequency that 
the amount of power required for barrage 
jamming is prohibitive. This situation may be 
the result of careful planning on the part of the 
enemy (and almost would have to be at the 
lower radar frequencies) or it may be almost 


accidental (especially in the microwave re- 
gion) . 

In case the enemy elects to place most of his 
radar in a relatively narrow band, with a few 
scattered sets outside this band, as was the case 
in the European Theater of Operations in World 
War II, a combination of barrage and spot jam- 
ming for complete coverage is clearly indicated. 


11.2.5 Types of Jamming Modulation 

The type of modulation employed for jam- 
ming purposes depends upon whether spot or 
barrage jamming is being employed, upon the 
vulnerability of the victim receiver to various 
types of modulation, and upon the kind of modu- 
lation that can be produced efficiently at the 
carrier frequency and power output at which 
the jammer operates. 

In the jamming of communications channels, 
one consideration in the choice of type of 
modulation is the psychological reaction of an 
operator to novel forms of interference. The 
modulation may be chosen to distract the op- 
erator rather than to obliterate the desired sig- 
nal. This technique is of particular importance 
when the jammer lacks sufficient power to mask 
the victim signal completely, since some form 
of distracting signal, although weaker than the 
victim signal, may succeed in preventing the 
reception of any great amount of intelligence. A 
distracting type of signal does not appear to be 
effective in radar jamming. Here, the desired 
display must be obliterated or confused if the 
jamming is to be effective. 

The type of modulation used for spot jam- 
mers should be such that the bandwidth of the 
jammer only exceeds that of the victim channel 
by an amount sufficient to allow for inaccuracies 
in aligning the jammer with the victim signal 
and for the frequency drift of the jammer and 
the victim channel. Barrage jammers should be 
provided with a form of modulation that dis- 
tributes the energy evenly over the band of 
frequencies that is being barraged. Further- 
more, the type of modulation must be such as to 
avoid “holes” through which the desired signal 
may be seen. In general, a random type of modu- 


GENERAL DESIGN CONSIDERATIONS 


217 


lation is more effective than a periodic type 
since, in many instances, antijamming [AJ] 
measures may be taken to cope with the latter 
kind of interference. 

Through poor design, some radar receivers 
may be very vulnerable to some simple form of 
modulation. Since it is often possible to obtain 
larger power outputs and relatively simple de- 
sign when simple types of modulation are em- 
ployed, such shortcomings of enemy equipment 
should be exploited. At the same time, the ease 
with which these weaknesses may be corrected 
must also be borne in mind, since the useful life 
of any offensive RCM device depends upon how 
difficult it is to devise an antidote and put it into 
service. Antijamming devices for simple types 
of modulation are discussed in Chapter 13. 

Although tests may indicate that a given re- 
ceiver is particularly vulnerable to a certain 
type of modulation, it does not necessarily fol- 
low in practice that this type is the best to use. 

In determining the best type it is necessary 
to give consideration to the practical aspects of 
employing this type of modulation in an actual 
transmitter. For example, one type of modula- 
tion may be found to be twice as effective as 
another; yet it may be possible, with a given 
amount of input power, to obtain four times as 
much output with the less desirable modulation. 
Under these circumstances use of the latter may 
be indicated. 

At the higher frequencies there is a practical 
limit to the modulation bandwidth that can be 
obtained. Furthermore, in the case of high- 
power radar barrage jammers a number of 
problems are encountered in connection with 
the modulation of the amount of power that is 
involved. An understanding of these problems 
will be of material aid in planning the use of 
such equipment and in future developments. 

Noise modulation, which is now almost uni- 
versally used for radar jamming, deserves spe- 
cial mention. Noise is a random type of modula- 
tion and one in which the energy distribution 
is uniform, except as it may be influenced by 
limitations in associated circuit elements. Noise 
modulation therefore lends itself particularly 
well to barrage jamming and, for that matter, 
also to spot jamming. Since it has no periodi- 
cally recurring frequency, it cannot be filtered 


out, or eliminated by any other means, without 
also eliminating the desired signal. As is well 
known, the noise level is the basic factor that 
limits the sensitivity of any receiver. Noise gen- 
erators for use in jamming transmitters are 
discussed in Chapter 2. 


Sideband Energy Distribution 

A knowledge of the distribution of energy in 
the sidebands of a modulated jamming trans- 
mitter is essential in planning the details of 
tactical application of the jammer, especially in 
barrage jamming. This is particularly true 
when a number of transmitters must be used 
to cover the band of frequencies involved. As 
detailed below, the distribution of sideband en- 
ergy considerably influences the manner of 
setting the carrier frequencies of the various 
transmitters involved in a barrage operation of 
this type. Information concerning the distribu- 
tion of the sideband energy is also vital to cal- 
culations of the effectiveness of a jammer for 
protecting a given target against a specific 
radar. 

Theoretically, the distribution of energy in 
modulation sidebands is confined to specific fre- 
quencies when recurrent waveforms are used 
for the modulation. Consequently, there are 
likely to be gaps in the spectrum. The widths of 
these gaps are a function of the parameters in- 
volved, and under some circumstances these 
types of modulation may be entirely unsatis- 
factory for the purpose in hand. 

In practice, the actual distribution of side- 
band energy may differ considerably from the 
theoretical values because of the characteristics 
of the electrical circuits involved. For example, 
there may be a considerable amount of inci- 
dental frequency modulation of the carrier. 
Under these circumstances, as compared to 
the theoretical distribution, relatively large 
amounts of energy are spread over a consider- 
able band in the vicinity of the carrier fre- 
quency. A transmitter having incidental fre- 
quency modulation is more effective in jamming 
receivers close to the nominal carrier frequency 
than if the frequency modulation were not pres- 
ent. The incidental frequency modulation allows 


218 


RADAR JAMMING TRANSMITTERS 


the carrier energy to be effective in jamming, 
even though AJ devices may be in use. 

When amplitude modulation is used, a large 
amount of the available output energy of a 
jamming transmitter may be dissipated in the 
carrier. This suggests the use of some form of 
carrier-suppressed emission in order that the 
total output capacity of the transmitter may be 
available in the modulation sidebands. 

A novel form of a carrier-suppressed (really 
carrierless) emission is employed in the Dina 
type of transmitter. In its basic form this trans- 
mitter consists of a direct-noise amplifier 
(whence the name Dina), designed to amplify 
in the r-f range in which transmissions are de- 
sired, which is connected to a source of noise. 
Noise components, at the desired frequency, are 
thus amplified until they have sufficient power 
to be radiated. Consequently, there is no carrier 
and all the available output capacity of the 
transmitter is made available in sideband en- 
ergy. 

In the design of Dina transmitters, difficulties 
arise from the necessity of tuning the wide- 
band amplifiers in order to choose the frequency 
band to be jammed. Greater flexibility and over- 
all simplicity may be achieved by generating 
the noise energy in a fixed frequency band and 
heterodyning to the desired transmission fre- 
quency. This method has the added advantage 
that it makes possible the use of the output of 
the noise source in the frequency range where 
it is most efficient. 

Another important consideration in the de- 
sign of jammers is the choice of the signal with 
which the carrier is modulated. If the carrier 
is modulated with a sine wave, the jamming 
may actually increase the amplitude of the pip 
in the enemy radar screen. This effect occurs 
because the pip “rides on top” of the jamming 
signal and the increased input to the second 
detector resulting from the jamming signal 
allows the second detector to operate on a more 
favorable portion of its characteristic. If the 
carrier is amplitude-modulated by noise that is 
highly clipped (i.e., noise in which the peaks 
have been cut off) and if the bandwidth of the 
radar receiver is wide in comparison with the 
jammer band, the resulting disturbance in the 
radar scope is flat-topped. The pip rides on top 


of such a disturbance, and consequently the 
jamming is ineffectual, even though the fre- 
quency coverage may be satisfactory. On the 
other hand, if the bandwidth of the radar is 
small in comparison with the jammer band- 
width, the resulting disturbance on the radar 
scope is sufficiently irregular to mask the pip 
effectively. This problem does not arise when 
the carrier is frequency-modulated by noise. 


^ Jamming Power Requirements 

In general, it is desirable to employ as much 
jamming power as possible. As a practical 
matter, however, the weight, bulk, portability, 
and power drain of the equipment often deter- 
mine the size of the transmitter that can be 
used. Furthermore, it is not economical on any 
score to provide jamming transmitters that are 
appreciably larger than necessary to accomplish 
the desired end. 

The exact calculation of the jamming power 
required in order to effectively neutralize a 
given radar system involves a knowledge of 
such factors as the power output of the enemy 
transmitter, the transmitting and receiving an- 
tenna gains and directivity patterns (in both 
the vertical and the horizontal planes) , the dis- 
tance between the jammer and the receiver, the 
strength of the desired (from the enemy view- 
point) signal at the receiver, the jam-to-signal 
[J/S] ratio for the type of modulation involved, 
and the effective size of the target. The exact 
mathematical relationships whereby the jam- 
ming power, for a specific case, may be calcu- 
lated are discussed in Chapter 6. The manner in 
which the various factors involved influence the 
jamming power requirements will be outlined 
here. A knowledge of these relationships is of 
considerable value, since, if the performance of 
a given jammer against a given enemy system 
is known, an accurate estimate can be made of 
its performance under slightly different condi- 
tions. 

In radar jamming, the closer the target is 
to the radar, the greater is the power required 
for jamming. This is so since the strength of 
the receiver echo increases as the distance be- 
tween the target and the radar decreases, and 


GENERAL DESIGN CONSIDERATIONS 


219 


more jamming power is therefore required to 
obliterate it. This condition exists even when 
self-screening is practiced (target carries a 
jammer) because, although the jamming sig- 
nal received at the radar thus increases as the 
target approaches, the size of the echo increases 
at a greater rate. For this reason, the minimum 
distance at which a jammer can screen a given 
target is a measure of the effectiveness of the 
jammer. In general, however, it is to be noted 
that considerably less power per channel is re- 
quired for radar jamming than for communica- 
tions jamming. This is true largely because of 
the fact that in the former it is necessary to 
obliterate only an echo, whereas in the latter 
it is necessary to cope with a direct signal. 

If the distance at which a jammer is effective 
is determined by experience for a given set of 
circumstances, the performance to be expected 
under other conditions may be estimated from 
the following relationships. Other factors being 
equal, the minimum distance at which a given 
radar jammer will be effective is: 

1. Directly proportional to the square root of 

a. the effective echo area of the target ; 

b. the effective peak power of the radar ; 

c. the power gain of the radar transmit- 
ting antenna; 

d. the jam-to-signal power ratio for the 
type of modulation employed. 

2. Inversely proportional to the square root 

of 

a. the jammer output power; 

b. the power gain of the jammer antenna 
in the direction of the radar. 

Jammer Frequency Setting 

If the jammers are otherwise in good operat- 
ing condition, the success of any plan of jammer 
activity depends entirely upon the accuracy 
with which the transmitters are adjusted to the 
victim frequency. In the manually adjusted 
transmitters used for spot jamming, therefore, 
means must be provided for determining the 
victim frequency and for accurately adjusting 
the jammer to this frequency. 

In spot jamming, the jammer carrier must be 
set as closely as possible to the frequency of the 
victim signal. In ground-based or ship-borne 


equipment this does not present a serious prob- 
lem since ample equipment and operating per- 
sonnel can generally be made available. In air- 
borne installations, on the other hand, the need 
for conserving weight and personnel makes it 
desirable to preset the jammer to the proper 
frequency on the ground before take-off. Unfor- 
tunately this cannot be done to spot jammers 
because of the setting accuracy that is re- 
quired. Deviations introduced by receiver or 
frequency meter calibration inaccuracies, by 
reading and resetting errors, and by frequency 
drifts in both the frequency meter and the 
transmitter due to changes in temperature, 
pressure, humidity, and power- supply voltages, 
all combine to make it impractical to preset spot 
jammers. The accuracy required is at least 0.5 
me or so in radar jamming. Overall accuracies of 
0.1 per cent or considerably better are evidently 
necessary. 

Even though it may not be feasible to preset 
an airborne spot jammer prior to take-off, the 
equipment should be adjusted before take-off as 
closely as possible to the frequency to be 
jammed. To make a major frequency change in 
the air is generally difficult and time-consum- 
ing. Furthermore, by setting the equipment as 
closely as possible to the desired frequency, the 
performance of the set can be accurately 
checked at approximately the frequency at 
which it will be used. 

As contrasted to spot jammers, barrage 
jammers can usually be preset to the proper 
frequency band and, in airborne equipment, 
the attention required during flight can thus 
be reduced to simply turning the equipment on 
and off at the proper time. 

The bandwidth of a radar barrage jammer 
is seldom great enough to cover the entire 
band over which the enemy radar is likely to 
be spread. Furthermore, because of the limited 
output power of all but the most recent types 
of available airborne barrage jammers, one or 
more units are generally required in each air- 
craft that is to be screened. When only one or 
two transmitters are involved in a given opera- 
tion, they should be accurately adjusted so as 
to span the spectrum in which the enemy radar 
carriers are most likely to be located. 

In large formations, however, where many 


220 


RADAR JAMMING TRANSMITTERS 


jammers are available, it is important that 
their frequencies be accurately adjusted so that 
the maximum possible number of channels are 
occupied by the jammer carriers. This may be 
done by carefully spacing the carriers uni- 
formly across the band occupied by the enemy 
systems. Under these circumstances the car- 
riers, particularly if they have incidental fre- 
quency modulation, contribute greatly to the 
jamming effectiveness. In an operation of this 
kind, the absolute accuracy of the frequency 
meter used for setting the carrier frequencies 
need not be very great since it is only the 
relative accuracy that is important, particu- 
larly if it is possible to check all transmitters 
against the same frequency meter. 

Automatically Tuned Jamming Equipments 

It is sometimes practical to use automatic 
devices that seek the victim signal, accurately 
align the jammer to its frequency, and then 
periodically monitor the enemy transmissions 
in order to terminate the jamming as soon as 
the enemy no longer uses the channel that is 
being jammed. Because of the feature of listen- 
ing through one’s own jamming, these devices 
are sometimes called “listening-through” sys- 
tems. 

A considerable number of laboratory designs 
for such equipment were perfected, and serious 
consideration was given to the widespread 
operational use of such devices, but no large- 
scale procurement was made, because of the 
rapidly changing tactical situation and other 
considerations. It must be remembered, for 
example, that some provision must be made 
to prevent several automatic jammers in air- 
borne applications from locking on one another. 
This difficulty does not arise in night operations 
or in isolated daytime flights, when the air- 
craft are likely to be separated from one an- 
other by considerable distances. 

The type of automatic operation that is used 
will depend upon the enemy system. For ex- 
ample, if the theater of operations is one 
wherein the enemy radars are so widely spaced 
that only one need be jammed at a time, the 
automatic operation may be one in which the 
jammer seeks the enemy frequency, transmits 
jamming signals thereon, and periodically 


listens through to see if the victim signal is 
still there. When it is no longer present, the 
jammer ceases to operate and then searches 
for the next signal to be jammed, repeating the 
whole process over and over again. This type 
of operation has one possible hazard. If the 
enemy should have available fighters that are 
equipped to home on the jammer-carrying 
aircraft, there is the possibility that the latter 
may be intercepted. 

Another type of operation would be one in 
an area in which there are many radars, a 
number of which may follow a given target at 
the same time. In this case, the automatic 
jammer operation may be one wherein the 
jammer seeks an enemy frequency, jams the 
first one encountered for a predetermined 
length of time (say from 30 sec to 2 min), 
then stops and seeks the next (as regards 
frequency) signal, jams it, and then moves 
on, etc. This type of operation can be effective 
against GCI and gun laying [GL] , even though 
all radars are not jammed all the time, since 
in either case accurate data are required for 
some period of time in order to make an inter- 
ception or to provide accurate data for gunfire. 
The type of jammer operation just described 
is also effective in preventing homing on the 
jammer by interception, since the length of 
time the jamming emission stays on any one 
frequency is relatively short. This type of 
operation is especially effective when used by 
a large formation of aircraft. In this case, the 
jammers will considerably outnumber the 
radars, so that the probability of a given radar 
remaining un jammed for an appreciable time 
is very small indeed. Radars will be unable to 
obtain direction-finding [DF] cuts on the 
jammers because of the constantly changing 
direction from which the jamming comes and 
because of the fact that they are generally 
receiving signals from two or more jammers 
simultaneously. 

It should be borne in mind that there is a 
simple counter-countermeasure for any listen- 
ing-through device that stops jamming and 
moves on to the next signal as soon as the 
victim signal disappears. The victim station 
would only have to interrupt his transmissions 
long enough for the jammer to note its absence 


GENERAL DESIGN CONSIDERATIONS 


221 


and to cease jamming. It would then be pos- 
sible to make use of the equipment that had 
been jammed, at least until the jammer again 
returned to its frequency. From the point of 
view of the jammers, difficulty on this score 
can be obviated by jamming any signal for a 
predetermined period of time without listening 
through. 

The Systems Approach 

Whenever it is necessary to employ spot jam- 
ming, the question of exactly what combination 
of transmitting, receiving, and indicating to 
use arises. The answer varies widely with the 
particular application. The first widely used 
spot-jamming setup consisted merely of a 
standard search receiver and three standard 
jamming transmitters. The operator simply 
listened to a signal, tuned a jammer to the 
signal, and then searched for another signal 
to jam, returning periodically to the original 
signal to monitor the effect of the jamming. 
With various portions of the spectrum assigned 
to different operators, a very creditable job 
was done with this comparatively simple equip- 
ment. 

A much more ambitious program than that 
described above may be necessary. This was 
first realized in connection with the design of 
ship-borne equipment, since in this case it is 
necessary to screen a very large target with 
moderate amounts of power. This frequently 
predicated the use of directional- jamming an- 
tennas, with the accompanying difficulty of 
locating the direction as well as the frequency 
of the enemy radar. These factors, together 
with the problems sometimes encountered of 
distinguishing between enemy and friendly 
radars at or near the same frequency and care- 
fully coordinating the activities of each jam- 
ming transmitter with other jamming trans- 
mitters on the same or other vessels and with 
other electronic gear which might be in use, 
made it desirable to develop a rather elaborate 
jamming system. Such a system consists of 
various receiving equipments with associated 
indicating devices (such as pulse analyzers and 
panoramic-presentation units), direction-find- 
ing equipments, jamming transmitters, an- 
tennas, suitable communications with various 


other points, etc. Examples of such systems will 
be discussed later. 

Besides the advantages listed above, such 
systems generally possess the additional im- 
portant feature that each component is 
specifically designed to function efficiently in 
the presence of the rest of the system. This 
is especially important in airborne work, since 
the various components must frequently work 
in close proximity to one another. It is also 
frequently possible to devise an integrated 
system which will eliminate some of the “extra"’ 
features of combinations of standard items 
(e.g., some of the features of search receivers 
designed purely for investigational work) with 
a corresponding saving in complexity and 
weight. These considerations, rather than the 
usual complexity of the job to be done, dictate 
the use of systems for airborne applications. 

Tactical Considerations 

Radar jamming transmitters should, as a 
rule, be used only as much as is necessary to 
accomplish the desired results. This practice 
will hinder DF and homing on the jammers by 
the enemy and, incidentally, will limit the time 
during which the enemy operators can study 
and become accustomed to the particular type 
of the jamming signal being used. As mentioned 
elsewhere, one of the most effective AJ meas- 
ures is sufficient operator training and experi- 
ence. Conversely, the element of surprise plays 
a large part in determining the effectiveness 
of a jamming operation. 

In radar jamming there is still another 
reason for limiting the use of the jammers as 
much as possible. When self-screening is used 
(that is, where the target to be screened from 
the enemy radar is carrying its own jammer), 
if the jammer is turned on before the craft 
is within the field of view of the radar, its 
presence will be revealed to the radar. This 
results from the fact that the strength of the 
emissions from the jammer considerably ex- 
ceeds the strength of the radar echo (except 
when the target is close to the radar) and, 
consequently, the radar receiver will respond 
to the jamming transmissions long before it 
receives a sufficiently strong echo to detect the 
presence of a target. Although neither the size 


222 


RADAR JAMMING TRANSMITTERS 


of the target nor its range can be ascertained 
by reception of jamming emissions, its bear- 
ing will be revealed and a warning given of the 
possibility of an attack from that quarter. 

An exception to the general philosophy of 
limiting jamming transmissions as much as 
possible would be in an instance in which a 
false appearance of activity is to be created. 
Just as in communications deception practices, 
if the enemy comes to associate jamming opera- 
tions with increased activity, it may be desir- 
able, on occasion, deliberately to operate jam- 
mers for deception and confusion purposes. 

Although the size and shape of a formation 
will undoubtedly be dictated by tactical consid- 
erations, it should be borne in mind that 
these factors also influence the jamming eifec- 
tiveness. The effectiveness of airborne radar 
jamming transmitters used for self-screening 
can be increased considerably if the formation 
of planes is made up so that the aircraft are 
all within the beamwidth but are not all within 
the distance corresponding to the radar pulse 
length. The jammers on all the planes will then 
contribute to the jamming effectiveness but 
only those planes which are within the distance 
corresponding to the pulse length will con- 
tribute to the amplitude of the echo. The echoes 
from the various aircraft will be spread on the 
radar screen and, therefore, the amplitude of 
the jamming signal needed to cover them up 
need not be so great as it would be if all echoes 
added together in height. 

11.3 TYPICAL TRANSMITTING 
EQUIPMENT 

Radar jamming transmitters fall into a rela- 
tively few fairly closely related categories ac- 
cording to intended use and power output levels. 
These categories, together with the character- 
istics of the various transmitters in each cate- 
gory, are shown in Table 1. The following com- 
ments are intended to amplify and explain 
Table 1. 

Low- and Medium-Power Conven- 
tional Tube Transmitters 

The accompanying monograph®®^ covers the 
technique developments used in the building 


of these transmitters in considerable detail. 
Most of the equipments listed consist merely 
of a tunable transmission line type oscillator 
(open-wire type line for conventional triodes, 
double-coaxial type line for lighthouse tubes) 
which is amplitude-modulated by a standard 
noise source and amplifier (see Chapter 2). 



I I 

I DINAMATE RECEIVER I 


Figure 1. Block diagram of Dina-Dinamate 

receiving and jamming equipment. 

The direct-noise amplifier type of jamming 
transmitter deserves special consideration, 
since the design of the transmitter itself is 
somewhat unusual and also since a ' ‘setting-on’^ 
receiver forms an optional component of the 
overall jammer. One of these equipments 
(AN/ARQ-8) will be described in some detail: 
the equipment (see Figure 1) consists of a 
suppressed-carrier transmitter (achieving the 
same result as the direct-noise amplifier) and 
a superheterodyne receiver operating over the 
same range as the transmitter. A control box 
is provided to allow operation from a remote 
position. In the example chosen, both the trans- 
mitter and receiver operate over the range 25 
to 105 me, with a power output of 20 w for the 
transmitter. The receiver r-f input and trans- 
mitter tank circuits have a bandwidth of 5 me 
so that satisfactory operation may be obtained 
over this incremental range by tuning only the 
oscillator, which is common to both units. 

The transmitter consists of a 150-kc wide 
noise source (which may be replaced by a 4 me 
wide noise source for barrage jamming) cen- 
tered at 20 me and a 45- to 85-mc heterodyning 
oscillator, plus a mixer stage and power ampli- 
fier. The r-f tank circuits, the mixer, and power 
amplifier are broad-band, as mentioned above, 
and tune over the range 25 to 105 me, so that 
tuning only the oscillator places the 150-kc wide 


TYPICAL TRANSMITTING EQUIPMENT 223 



Table 

1. Radar jamming transmitter developments. 

1 

Identification 

Nos. 

Use 


Tuning 
range (me) 

Power 

output 

(watts) 

References 

Comments 


Loiv- and medium-power conventional tube transmitters 


RRL: B-1700 

Div. 15: RP-162 
Navy: CXCE 

Ship-borne practice 
jammer 

85-115 

15 

511 


RRL: B-2000 

Div. 15: RP-163 
Army /Navy: 
AN/SPT-3 

Airborne or 
borne 

ship- 

85-135 

10 

365, 531 

Modification kit available to 
convert frequency range 
to 125 to 150. 

RRL: B-4500 

Div. 15: RP-163 

Airborne 


70-250 

20 


Revision of above trans- 
mitter, employing same 
principal components, etc. 

RRL: B-2200 

Div. 15: RP-309 
Army /Navy: 
AN/APT-1 
AN/SPT-1 

Airborne or 
borne 

ship- 

90-220 

12 

409, 462 

Direct-noise amplifier. Mod- 
ification available (but 
never produced in quan- 
tity) incorporating “set- 
ting-on” receiver. 

RRL: B-2800 

Div. 15: RP-218 
Army/Navy: 
AM-14/APT 

Power amplifier 

85-150 

140 

362 

Amplifier for above trans- 
mitters. 

RRL: B-3400 

Div. 15: RP-329 
Army /Navy: 
AM-18/APT 

R-f amplifier 


140-210 

50 

396 

Amplifier for above trans- 
mitters. 

RRL: B-2900 

B-3200 

Div. 15: RP-250 
RP-207 

Army/ Navy : 
AN/ARQ-8 

Airborne or 
borne 

ship- 

25-100 

30 

367, 421, 
557 

Direct-noise amplifier. In- 
cludes “setting-on” re- 
ceiver. 

RRL: B-4100 

Div. 15: RP-344 
Army /Navy: 
AM-33/ART 

R-f amplifier 


26-105 

150 

110 

Primarily intended for use 
with above transmitter. 

RRL: F-1500 

Div. 15: RP-164 
Army/Navy: 
AN/APQ-2 
AN/SPT-4 

Airborne or 
borne 

ship- 

200-550 

15 

704 

Modification available to 
extend frequency range 
down to 150 me. 

RRL: F-902 

Div. 15: RP-165 
Army/Navy: 
AN/APT-2 
AN/SPT-2 

Airborne or 
borne 

ship- 

450-720 

5 

360, 440, 
541, 619, 
652 


RRL: F-4300 

Div. 15: RP-165 
Army /Navy: 
AN/APT-2A 






Revision of above trans- 
mitter to provide single- 
dial tuning and other 
improvements. 

RRL: F-2500 

Div. 15: RP-166 
Army/Navy: 
AN/APQ-9 
AN/SPT-5 

Airborne or 
borne 

ship- 

475-585 

20 

360, 447, 
558 



224 


RADAR JAMMING TRANSMITTERS 


Table 1. {Continued) 


Identification 

Nos. 


Use 


Tuning 
range (me) 


Power 

output References 
(watts) 


Comments 


RRL: F-8500 Airborne 

Div. 15: RP-336 
Army /Navy: 

AN/APT-5 


350-1,200 15 472, 645, Can be tuned to 1,400 me. 

694 Modification can be made 
to allow tuning down to 
200 me. 


RRL: F-3505 Ship-borne 

Div. 15: RP-275 
Navy: AN/SPT-6 

RRL: F-4800 Airborne 

Div. 15: RP-428 
Army/ Navy: 

AN/APT-9 


350-1,200 15 472, 645, Ship-borne modification of 

683 above transmitter. 


300-2,500 15 


Can be modified to tune 
down to 200 me. Part of 
AN/APQ-21 jamming 
system described below. 


RRL: F-3300 
Div. 15: RP-285 
Navy: TDY/CXFR 


RRL: F-3400 
Div. 15: RP-338 
Army /Navy: 
AN/APT-4 


RRL: F-4400 
Div. 15: RP-338 
Army/ Navy : 
AN/APT-8 

RRL: A-500 
Div. 15: RP-lOO 
Army/Navy: 
AN/MPQ-1 


RRL: F-1800 
Div. 15: RP-167 
Army /Navy: 
AN/APQ-1 

RRL: U-600 
Div. 15: RP-380 
Army/Navy: 
AN/APA-27 

RRL: S-1200 
Div. 15: RP-458 


RRL: F-4500 
Div. 15: RP-414 
Army/Navy: 
AN/APQ-20(XA-1) 


Ship-borne 


Airborne 


Airborne 


Medium- and high-power transmitters 

350-800 150 Later modifications made by 

manufacturer extended 
frequency range above 
and below that given. 

150-400 150 466, 606, Uses separate tubes for 

350-780 642 separate ranges. Another 

modification developed 
(AN/APT-7), but not 
produced, extending fre- 
quency range down to 90 
me. 


750-1,200 100 Airborne magnetron trans- 

mitter developed but 
never produced. 


Ground-based 
against AI 


480-500 50,000 353, 587, Several units built for use 

720 in England. 


Automatic jammers and jamming systems 

Automatic jamming 475-585 5 358 

transmitter 


Sweeps any 40-mc band 
within frequency range. 


Automat automatic 
jammer control 


Depends upon 
jamming 
transmitter 
used 


GL airborne jam- 
ming system 


Band around 
200 me 


Airborne jamming 2,300-4,200 
system 


15 


10 


481 Control unit for use with 
standard search receiver 
and many standard jam- 
ming transmitters. 

Employs AN/APQ-2 trans- 
mitter listed above plus 
standard search items in 
long-shaped case. Pro- 
vided with slot antennas. 

Includes klystron trans- 
mitter plus standard re- 
ceiver, panoramic adapter, 
antennas, filters, etc. 
Ship-borne modification 
also designed. No large 
procurement because unit 
was superseded by follow- 
ing items. 


TYPICAL TRANSMITTING EQUIPMENT 225 


Table 1. {Continued) 

Identification 

Nos. 

Use 

Tuning 
range (me) 

Power 

output 

(watts) 

References 

Comments 

RRL: F-5100 

Div. 15: RP-424 

Army /Navy: 
AN/APQ-20(XA-2) 

Airborne jamming 
system 

2,230-4,030 

50 

688 

Complete system includes 
magnetron transmitter 
plus standard receiver, 
panoramic adapter, fil- 
ters, antennas, etc. 

RRL: F-5150 

Div. 15: RP-424 

Army /Navy: 
AN/APQ-27 

Airborne jamming 
system 

2,230-4,030 

50 


Same as above, except in- 
cludes remote tuning and 
other improvements. 

RRL: F-4800 

S-1400 

Div. 15: RP-428 

Army /Navy: 
AN/APQ-21 

Airborne jamming 
system 

1,000-2,500 

15 


Includes AN/APT-9 trans- 
mitter described above 
plus standard receiver, 
panoramic adapter, etc. 

RRL: F-9000 

Div. 15: RP-457 

Navy: XMBT 

Ship-borne jam- 
ming system 

2,000-4,000 

90-260 

1,000 

See text 

See text for complete de- 
scription. 

Army /Navy: 
AN/TPT-1 

In ground-based 
jamming system 

90-220 

100 or 50 


Consists of AN /APT-1 plus 
associated amplifiers and 
directive antennas for 
ground-based operation. 


noise band anywhere in a preselected 5-nic por- 
tion of the 25- to 105-mc range. The lower 
sideband developed by heterodyning the 45- to 
85-nic oscillator with the 20-mc noise source 
becomes the output frequencies 25 to 65 me 
and the upper sideband similarly becomes the 
output frequencies 65 to 105 me. The trans- 
mitter may be used quite independently of the 
receiver, especially when provided with the 
wide-band modulator mentioned above for bar- 
rage jamming. 

The receiver is designed to work in conjunc- 
tion with the transmitter by using the oscillator 
in the transmitter as its local oscillator. Since 
the transmitter operates at a frequency that is 
20 me higher or lower than its oscillator fre- 
quency, the use of a 20-mc i-f amplifier in the 
receiver permits setting the transmitter on the 
desired frequency by merely tuning in the re- 
ceiver on the signal to be jammed. 

The circuit matching the antenna to the 
mixer of the receiver is 5 me wide. The antenna 
tuning is preset to the 5-mc frequency range 
desired and any station in that range may be 
tuned in by varying only the transmitter oscil- 
lator. Thus, the complete system is tunable 


over the 5-mc incremental band by means of a 
single control. 

As shown in the chart, a higher-frequency 
version of this equipment (AN/APT-1) is also 
available. There are also r-f amplifiers available 
for use with the transmitter to increase the 
power output to well over 100 w over most of 
the frequency range. 


11.3.2 Medium-Power Magnetron and 
High-Power Transmitters 

The medium-power magnetron transmitters 
listed in Table 1 need very little comment except 
that given under the discussion of techniques in 
the accompanying monograph.®^^ Reports have 
been issued describing the general features^®® 
of, and the results obtainable®®®* ®^2 with, these 
transmitters. 

The very high-power ground-based jamming 
transmitter listed requires some special com- 
ment. This transmitter employs the resnatron 
tube (described elsewhere®®®) and is a complete 
jamming unit consisting of seven trucks, in- 
cluding power supplies, highly directive anten- 


226 


RADAR JAMMING TRANSMITTERS 


nas, etc. The unit was designed for use against 
the German night fighters equipped with AI 
radar. It was intended to provide a lane of 
safety^®^ for bombers along a selected route. The 
construction and operation of the unit, which 
was extremely complex, is described else- 
where.®^"^’ 


11.3.3 Automatic Jamming Transmitters 
and Jamming Systems 

As indicated in Table 1, several automatic 
jamming transmitters and several jamming 



Figure 2. Block diagram of Automat auto- 
matic jammer setting-on equipment. 


systems have been developed. One of these au- 
tomatic jammers and two of the jamming sys- 
tems will be described as examples of the type 
of design employed. 

Automatic Jamming Transmitters 

Several attempts to design a satisfactory au- 
tomatic jamming system, especially for the pur- 
pose of eliminating the necessity of carrying op- 
erators on spot- jamming missions in the Euro- 
pean Theater of Operations, were made but, 
although two equipments were developed, no 
large-scale production was ever completed. One 
of these equipments was actually a modification 
of the AN/ APT-2 transmitter, providing an 
autodyne receiver for use with the transmitter 
but using the same oscillator circuits, modu- 
lator circuits, etc., as the original transmitter. 


This modePi® was carried to the stage of pre- 
production engineering by a manufacturer, but 
changes in tactical situations made it unneces- 
sary to go through with extensive production 
plans. 

A parallel development^^ was carried out to 
accomplish the same results in a somewhat 
more general manner. This development (Pim- 


RECEIVING EQUIPMENT 

/APR-5A AN/APA-41 



AN /APT- 10 TRANSMITTER 



Figure 3. Block diagram of AN/APQ-20 S-band 
airborne jamming system. 


pernel) made use of a separate receiver and 
drive unit which first tuned in the signal and 
then tuned an AN/ APT-2 or other similar 
transmitter to the signal frequency. 

With these fairly early approaches as a basis, 
an attempt was made to develop a generally use- 
ful automatic jamming attachment. This sys- 
tem (Automat) consisted of a device which was 


TYPICAL TRANSMITTING EQUIPMENT 


227 


to be used in conjunction with a standard search 
receiver and a standard jamming transmitter 
to convert the combination into an automatic 
jamming system. Small motor-drive units are 
supplied to attach to the front panels of the 
receiver and transmitter for automatically 
sweeping them over a selected frequency range. 
Separate antennas for receiver and transmitter 
are required. The receiver antenna is used by 


frequency. A modification of this first method 
is to use the transmitter' as a barrage jammer 
and the receiver as an ordinary search receiver. 
The second method of operation involves manu- 
ally tuning the receiver to the signal which it is 
desired to jam and then allowing the system to 
lock the jamming transmitter on frequency. 
The third method of operation is completely 
automatic. The receiver automatically sweeps 


RECEIVING ANTENNAS I TRANSMITTING ANTENNAS 



S9000 SYSTEM 

Figure 4. Block diagram of Elephant ship-borne jamming system. 


the receiver to pick up the jammer. Since there 
are no mechanical connections between units, 
they may be mounted in any relation to one 
another. A block diagram of this jamming 
system is shown in Figure 2. 

This equipment may be operated in three 
separate ways. In the first place, completely 
manual operation may be employed ; that is, the 
receiver may be tuned to a signal by hand and 
the transmitter tuned by hand to the receiver 


the selected frequency band and stops on the 
first signal received. The transmitter then 
starts sweeping, locks on the receiver frequency, 
and jams for 1/2 to 7 min, depending on the 
settings of the time-delay circuit. At the end of 
the jamming period, all relays are restored to 
starting positions. At this point, several differ- 
ent methods of operation are possible, depend- 
ing on the selected position of switches inside 
the unit. Any combination of the following re- 


228 


RADAR JAMMING TRANSMITTERS 


ceiver and transmitter functions may be used. 

1. Receiver relocks on same signal without 
moving (if signal is still there) . 

2. Transmitter relocks on receiver without 
sweeping. 

3. Transmitter leaves receiver frequency and 
resweeps before locking on. 

4. Receiver leaves signal and locks on next 
signal encountered. 

The Automat circuits are operated from the 
intermediate frequency taken from the pano- 
ramascope output connector on a standard 
search receiver (such as AN/ APR-4). This 
signal is fed through a high-pass filter into a 
converter tube and heterodyned with a 30-mc 
oscillator, thus forming video frequencies which 
are amplified and applied to a trigger circuit, 
the output of which is rectified and operates 
the necessary relays for the receiver and trans- 
mitter drive motors, and the automatic locking 
clutches. 

A modification of the above-described system 
has been developed which responds only to 
pulses and which omits the operation listed as 
No. 4 in the preceding paragraph. 

As mentioned earlier in this chapter, no wide- 
spread tactical uses of these units have been 
made, because of rapidly changing situations. 
It is felt, however, that under different circum- 
stances, such devices might be of very consid- 
erable use. 

Airborne Jamming Systems 

As shown in Table 1, several airborne jam- 
ming systems have been developed. One of these 
is described in detail, as an example of the 
type of design employed. These systems are 
generally quite similar except for frequency 
range covered and minor details of construc- 
tion, and further details may be obtained from 
the references cited. 

A block diagram of the AN/APQ-20 (XA-2) 
jamming system is shown in Figure 3. This 
system is a complete, manually tuned spot- 
jamming equipment consisting of receiving 
equipment and a jamming transmitter. The 
receiving equipment includes a panoramic- 
presentation unit for use in setting the jammer 


on the received signal. The essential compo- 
nents of the system are an AN/ APR-5 receiver 
and an AN/APA-41 panoramic adapter (see 
Chapter 10), an APT-10 (XA-2) transmitter, 
and several antennas (see Chapter 4). A band- 
pass filter to prevent reception of spurious sig- 
nals is also provided. 

Ship-Borne Jamming Systems 

One very complete ship-borne jamming 
system has been developed.®^”^ This complete 
ship-borne jamming system (Elephant) was 
the result of an attempt to develop an integrated 
jamming system for operation at frequencies 
from 1,000 me up. One complete experimental 
system for operation only in the S band has 
been built and tested on sea trials. Other units, 
designed for use with this system and built but 
not completely tested, are a low-frequency r-f 
unit for the transmitter and a high-frequency 
(6,500 to 11,000 me) tuner unit for the receiver. 
A schematic-assembly view of the system is 
shown in Figure 4 . 

The receiving equipment consists of a dual 
receiver and a standard Navy Type DBM radar 
DF equipment (see Chapter 10). The dual re- 
ceiver provides one receiving channel to operate 
as a search receiver, while the second identical 
receiver with separate antennas operates as a 
monitor receiver for observing the signal which 
is being jammed by the transmitter. The direc- 
tion finder is used in conjunction with the 
search receiver to obtain a bearing on the signal 
to be jammed and as an aid in the identification 
of signals. The receivers provide single-signal 
reception over a tuning range of 2,000 to 4,000 
me, present the signal on an oscilloscope, and 
indicate on meters the pulse width and prf of 
the signal. 

The transmitter is a 1-kw noise-modulated 
transmitter composed of a main transmitter 
console housing the modulator, power supplies, 
control equipment, and the Mark III r-f unit 
which consists of the tunable magnetron oscil- 
lator. This magnetron is tunable between 2,460 
me and 3,610 me. The r-f output of the trans- 
mitter is fed to the transmitter antenna system 
through a wave guide. Two rotatable direc- 



TYPICAL TRANSMITTING EQUIPMENT 


229 


tional antennas are connected through a Y 
switch so that selection of the one providing 
unobstructed radiation may be made. These 
narrow-beam antennas permit full 360-degree 
coverage in azimuth. The vertical beamwidth 
is sufficient to allow for roll of the ship. Radi- 
ation is circularly polarized. Another wave- 
guide switch permits the transfer of the trans- 
mitter output to a dummy antenna during 
standby or tuning operations. 


11.3.4 Expendable Transmitters 

No development work was undertaken by 
Division 15 on expendable transmitters for 
radar jamming. A theoretical study of one 
such device was made with the conclusion^^s 

that such equipment might be useful under 
rather specialized circumstances but was not 
of enough general interest to warrant an ex- 
pensive developmental program. 


Chapter 12 

RADAR DECEPTION AND CONFUSION 


121 INTRODUCTION 

V ARIOUS IMITATIVE methods designed to cre- 
ate confusion or deception of enemy radar 
operation have been developed. For convenience, 
these devices may be classified into mechanical 
and electrical means. In addition, just as in the 
communications field, manipulative counter- 
measures deception may also be practiced. 

Under the category of mechanical confusion 
there are various reflector devices which act 
as decoy targets. They serve to confuse (and 
sometimes deceive) the radar operator by cre- 
ating false signals which closely resemble those 
from a legitimate target. These reflecting sur- 
faces are generally known as Window. The 
use of such material for creating confusion is 
known as a Window operation. 

Electrical deception may be carried out by 
means of specially developed devices or by using 
the jammers previously described in this pub- 
lication. To do this, a small diversionary force 
carries enough jammers to make it indistin- 
guishable from the genuine attacking force 
carrying jammers for its own protection. This 
will be elaborated upon later. 

Manipulative radar countermeasures decep- 
tion, as the name implies, is the use of counter- 
measures devices to mislead the enemy as to 
our intentions by creating such activity at 
times other than when an actual offensive oper- 
ation is under way. The importance of counter- 
measures at times other than during an actual 
operation cannot be too strongly emphasized. 
Prisoner-of-war reports indicated that, in cer- 
tain theaters, advance notice of impending op- 
erations was always given to the enemy by the 
appearance of intensive countermeasures ac- 
tivity. 

Radar manipulative deception requires care- 
ful attention to details. Search receivers can 
readily determine the enemy radar equipment 
that is in operation and countermeasures activ- 
ity may then be directed against it in order to 
attract attention. Furthermore, it may be pos- 
sible to determine the success of such activity 


by observing whether the enemy radar ceases 
operation, shifts to another frequency, or other- 
wise changes its normal plan of operation. 

Most of the work on deception and confusion 
methods was done by the Radio Research Lab- 
oratory under contract OEMsr-411. Important 
contributions were made, especially to the work 
on corner reflectors (Kites or Angels) and to 
the work on electrical deception devices, by 
the General Electric Company under contract 
OEMsr-931. 


12 2 general description of window 

The various types of Window can be divided 
simply into two classes, tuned and untuned. The 
tuned varieties respond most effectively over 
fairly narrow frequency bands of the order of 
plus and minus 7 to 10 per cent, while the 
untuned varieties respond to much wider fre- 
quency bands. No practical form of Window, 
however, acts independently of frequency, and 
all that have been used show a maximum effi- 
ciency at some frequency. 


^ Types of Window 

Tuned Window consists normally of dipoles 
that give a maximum power response when cut 
to half wavelength (0.475 wavelength for 
straight dipoles). The response is still appre- 
ciable near multiples of the fundamental fre- 
quency, decreasing somewhat more slowly than 
the inverse square of the frequency ratio. When 
several graded lengths of dipoles are packaged 
together, the practical distinction between 
tuned and untuned Window is obscure, although 
the distinction remains clear from the view- 
point of theory and design. 

The following types of Window have proved 
to be of varying practical value. 

1. Tuned reflectors (dipoles). 

a. Chaff,'^ narrow strips of embossed or 

« Manufactured and used in quantity. 


230 


GENERAL DESCRIPTION OF WINDOW 


231 


paper-backed aluminum foil, bent lon- 
gitudinally into a flattened-V cross sec- 
tion by means of Chaff cutters. 

b. Flat Chaffs (British Window), cut by 
guillotine from paper-backed aluminum 
foil. 

c. Tuned Rope, consisting of dipoles in 
longitudinal sequence, physically sup- 
ported by means of a nonconducting 
medium. 

d. Wires. 

e. Turnstiles, each made from three dipoles 
held mutually perpendicular at their 
centers. 

2. Untuned reflectors. 

a. Rope,'" 400-ft streamers of narrow (V 2 - 
in.) foil, packaged three rolls per 
bundle. 

b. Corner reflectors (Angels or Kites), 
constructed from three mutually per- 
pendicular planes of conducting ma- 
terial, and diplanes, constructed from 
two mutually perpendicular planes of 
conducting material. 

c. Squares or sheets. 

The following sections present a more de- 
tailed description of the design and manufac- 
ture of the above types of reflectors and a brief 
discussion of the properties of each. A tabula- 
tion of manufactured types of Window is in- 
cluded in Table 1. 


Chaff 

The elementary theory of Chaff^®^* 
shows that the radar echo of a half-wave dipole 
is only slightly dependent upon the cross sec- 
tion of the dipole. The width of the frequency 
band of the Chaff response varies rather slowly 
with the width of a thin strip, approximately 
as the one-third power. As a consequence of 
these facts, a given radar echo can be obtained 
with a minimum weight and volume of Chaff 
if the dipoles are made as thin and as narrow 
as possible. A simple calculation will show that, 
if it is desirable to cover a wide frequency 
band, the use of two or more lengths of very 
narrow strips will result in lighter weight and 
b Manufactured and used in quantity. 


less volume than the use of wide strips. Because 
weight and volume are prime considerations 
when Window is to be carried in aircraft, every 
effort has been made to reduce the width and 
thickness of the strips to a minimum value. 

The most suitable material for Chaff is 
aluminum foil. It is a lightweight conductor 
which can be produced in quantity and rolled 
easily to extreme thinness. The thickness of the 
foil and the width of the strip cannot, however, 
be reduced indefinitely in order to reduce the 
weight and volume of the Chaff. A practical 
consideration must be met, viz., the individual 
strips in a package must separate when the 
package is opened in the air. The consequence 
of too light a foil or too narrow a strip is that 
the dipoles coalesce into a mass when released 
in the air and have no opportunity to function 
individually in producing a radar response. 
The phenomenon is known as “birdnesting” 
and has been a controlling factor in fixing the 
lower limit of thickness and width of Chaff 
dipoles. 

As a means of obtaining greater rigidity in 
narrow strips of thin foil, a machine was de- 
signed to cut the strips from a continuous sheet 
and to give the individual strip a longitudinal 
bend resulting in a flattened-V cross section. 
This method of manufacture has been adaptable 
to mass production in great quantities and 
produced an exceedingly light type of Chaff. 
The so-called Chaff cutting machines (Figures 
1 and 2) operate on the principle of the lawn 
mower in that a rotary set of blades cuts 
against a fixed blade. A sheet of foil is fed 
continuously into the cutter, the width of the 
sheet having been pre-slit to the desired length 
of the dipoles. The longitudinal fold of each 
dipole is produced by alternate blades of the 
rotary cutter which have been ground back in 
order to bend rather than to cut the foil. Hence, 
as the sheet is fed continuously into the cutter, 
each dull blade produces a fold and each sharp 
blade cuts off the bent strip. Present machines 
cut 10 strips per revolution and about 8,000 per 
minute. As many as four layers of foil are often 
cut simultaneously, thus greatly increasing the 
production rate, but, when more than one layer 
is cut at a time, the speed of the machine is 
somewhat reduced. 


232 


RADAR DECEPTION AND CONFUSION 


The practical limit of foil thickness has approximately 10 in., as in the Army Chaff 
proved to be slightly less than 0.001 in. Large RR-4/U (Figure 3) used against the German 
quantities of thickness 0.0008 in. and also of Wurzburg, .the birdnesting amounts to 10 to 25 
0.0009 in. have been manufactured. Widths of per cent. The frequency band from the resonant 

Table 1. Types of Chaff and Rope. 

Type 

S' ‘-•y 

Band 

covered 

(me) 

Polari- 

zation 

Units 

per 

bundle 

Gross 
bundle 
wt (lb) 

Number 

of 

pieces 

Lengths* 

Width 

(in.) 

Foil 

(in.) 

Remarks 

RR-2/U CHR-1 

-350 

Vertical 


0.8 

3 

400' 

0.50 

0.0009 

hard 

Each of 3 rolls in inner 
sleeve 

parachute, and 15-ft. 
cloth leader. 

RR-3/U CHR-2 

-350 

Both 


0.8 

3 

400' 

0.50 

0.0009 

hard 

Each of 3 rolls in inner 
sleeve i^X 33^X3^", 
3" sq. card, and 15-ft. 
cloth leader. 

RR-9/U 

182-212 

Both 

1 

0.35 

250 

28K" 


0.00035 

soft 


RR-18/U 

182-212 

Both 

4 

0.9 

660 

28K" 


0.0009 

hard 

Strips stacked in three 
layers in form of fore- 
shortened S. 

CHB-1 

193-224 

Both 

1 

0.35 

250 

27" 

Vs 

0.00035 

soft 


RR-16/U CHA-25-(3) 

320-600 

Both 

3 

0.64 

3X2,400 

15K" 
12, 10" 

0.060 

0.0009 

hard 


RR-ll/U CHA-2-(3) 

335-390 

Both 

3 

0.23 

2,200 

151^" 

0.060 

0.0009 

hard 


RR-4/U CHA-28-(3) 

450-600 

Both 

3 

0.32 

2X3,000 

111^" 

10" 

0.045 

0.0009 

hard 


RR-5/U CHA-3-(3) 

520-600 

Both 

3 

0.19 

3,600 

10" 

0.045 

0.0009 

hard 


RR-19/U CHA-35-(3) 

600-875 

Both 

3 

0.45 

2X6,000 

8^" 

rVs" 

0.045 

0.0009 

hard 


RR-8/U CHA-4-(3) 

660-770 

Both 

3 

0.25 

6,000 

7K" 

0.045 

0.0009 

hard 


RR-20/U. CHA-45 

860-3,000 

Both 

1 

0.35 

4X6,000 

5y2" 

3 A" 
2^" 

0.035 

0.0009 

hard 


CHA-5-(3) 

2,700-3,400 

Horizontal 

3 

0.6 

60,000 

1 27 // 

0.045 

0.0009 

hard 


RR-6/U 

2,700-3,400 

Both 

2 

0.5 

50,000 

1 27 // 

-1 32 

0.045 

0.0009 

hard 

Paper backing glued 34 
to ^ of length. 

RR-7/U 

2,700-3,400 

Horizontal 

1 

Net 

90db5g 

20,000 

1 27 // 
^32 

0.045 

0.0009 

hard 

Load for 60-mm mortar 
shell (T-15, 16, 17). 
Load for 81-mm mortar 
shell (T-22). 

RR-IO/U 

2,700-3,400 

Horizontal 

2 

Net 

150 ±5g 

35,000 

1 11 ." 
^32 

0.045 

0.0009 

hard 

RR-24/U 

2,700-3,400 

Horizontal 


Net 10,000 

45±2.5g 

1 27 // 
^32 

0.045 

0.0009 

hard 

Load for rifle signal 
grenade (T-62). 

CHW-5 

2,500-3,200 

Horizontal 


0.35 

5,000 

2" 

0.020 

0.006 

soft 

Used for identification 
purposes. 

RR-12/U 

8,000- 

Both 

1 

2.5 

100,000 

_ 9 _// 

16 


0.00035 

soft 



♦All strips longer than 20 in. were flat; all shorter were crimped. 


the order of %8 in. proved most practicable. 
Embossed foil is superior to plain foil of the 
same thickness. The use of a thinner foil or a 
narrower width tends to increase the birdnest- 
ing. In a bundle of 6,000 dipoles, of length 


frequency to the half-power point is approxi- 
mately ±7 per cent in material of the present 
ratio of length to width. 

The upper limit of frequencies practical for 
Chaff is determined by polarization of the 


GENERAL DESCRIPTION OF WINDOW 


233 


radar. Tests have shown that for Chaff dipoles 
several inches or more in length the orientation 
in the air after release is approximately ran- 
dom. Shorter dipoles, of the order of 3 in. in 
length or less, tend to fall in a horizontal posi- 




Figure 1. Chaff cutter: cross-sectional view of 
cutting blades showing bending and cutting 
operations. 


paper backing is used but it is glued only to 
one end of each dipole. As a consequence, the 
unattached end of the tissue backing acts simi- 
larly to the feather on an arrow in orienting 
the dropping dipole vertically. This S-band 
Chaff is known as RR-6/U (Figure 4). The 
imperfections and irregularities in manufac- 
ture are such that the horizontal and vertical 
responses from RR-6/U are approximately 
equal. 

At higher frequencies, however, where the 
dipole length is shorter than an inch, the 
method of manufacture utilized for S-band 
Chaff becomes difficult and the desired effect 
has not been obtained by any known type of 
Chaff in which half-wave dipoles are used. The 
upper limit, therefore, for unpolarized resonant 
Chaff is of the order of 5,000 me. At frequen- 
cies possibly up to 30,000 me. Chaff is still 
fairly economical as regards weight and volume 
but will respond only to horizontal polarization. 
The use of longer Chaff, utilizing the resonance 
at multiple frequencies, however, has not been 




Figure 2. The first Chaff cutter. 

tion. As a consequence, when such h-f Chaff is 
observed by a radar in vertical polarization at 
a moderately low elevation, the responses are 
negligible as compared to those in horizontal 
polarization. For that part of the radar spec- 
trum where the lengths of the dipoles are of 
the order of 2 in., a special type of Chaff has 
been devised to overcome this difficulty. A thin 


Figure 3. RR 4/U (CHA-28-3) Chaff used 
against the Wurzburg band (450-600 me). 

fully explored in this frequency region. The 
Chaff technique developed to date is thus ap- 
plicable in the radar frequency band from 
approximately 300 to 5,000 me for all polariza- 
tions. Weight and volume considerations, how- 
ever, vary considerably over this range. A few 
simple applications of elementary theory will 
show how this variation occurs. 

For convenience, a unit of Chaff or Window 
has been defined as a quantity sufficient, at the 
resonant frequency, to give a radar echo equal 
to that of a B-17 airplane seen head on. This 



234 


RADAR DECEPTION AND CONFUSION 


definition is theoretically unsatisfactory and 
practically impossible to measure with preci- 
sion but has proved exceedingly useful in prac- 
tice. Theoretical considerations show that the 
number of dipoles required to produce a con- 
stant effective echoing area varies as the square 
of the frequency. Because the effective echoing 
area of an aircraft is not highly dependent 
upon frequency and because the dependency is 
not well known, it may be assumed that over 
the present radar spectrum a unit response 
corresponds to a constant echoing area (about 



Figure 4. RR 6/U half-glued Chaff for use in 
both polarizations against the 2,700- to 3,400-mc 
band. 


500 sq ft). This assumption is certainly not 
precise but may be adopted for purposes of 
discussion. Consequently, the number of dipoles 
per unit varies as the square of the frequency. 
The length of the individual dipole varies in- 
versely as the frequency. If Chaff could be made 
from a material of constant thickness with a 
constant ratio of length to width, it is clear 
that the weight of a single dipole would vary 
inversely as the square of the frequency. The 
weight of a unit of Chaff would then be inde- 
pendent of the frequency. It has proved impos- 
sible, however, to build Chaff that follows this 
relationship. At higher frequencies the width 
of the dipoles would be exceedingly small and 
the birdnesting excessive. Practically, there- 
fore, the width of the dipole decreases only 
slightly with decreasing length and the weight 
per unit increases nearly as rapidly as the fre- 
quency. The volume of a bundle, however, in- 


creases somewhat more slowly than the weight. 

In view of the circumstances outlined above, 
it is fortunate that the German Wurzburg radar 
system happened to lie in the 450- to 600-mc 
band, the optimum frequency band for Chaff.^^^ 
As a result it was possible to manufacture Chaff 
with a weight of only 1 oz per unit for a 13 per 
cent bandwidth. Early British Window or flat 
Chaff, cut by guillotine from flat strips, weighed 
27 oz per unit and covered only approximately 
twice the frequency bandwidth of bent Chaff. 
Improvements by the British, however, finally 
brought flat Chaff into competition with bent 
Chaff as regards weight and volume. 

Extensive testing and experimenting have 
led to a triangular sleeve-type of self-opening 
bundle for Chaff 7 in. or more in length (Fig- 
ure 3). A simple roll of paper, although fairly 
satisfactory, is much more difficult to load prop- 
erly without damaging the Chaff and also gives 
somewhat greater birdnesting. A flat bundle 
(Figure 5) is also fairly satisfactory but suffers 
from the same difficulties as the simple roll 
and is proportionally heavier. All types of 



Figure 5. Radio operator of B-17 dispensing 
CHA-3 through chute in window of radio room. 


bundles for hand dispensing from aircraft are 
unsealed. When mounted on double tapes for 
automatic dispensing, the seal is automatically 
broken on release from the tape (for dispensing 
techniques and equipment see Chapter 14) . For 
short Chaff, such as RR-6/U, a narrow box- 
type bundle is required (Figure 4). A box with 
closed ends prevents the small dipoles from 




GENERAL DESCRIPTION OF WINDOW 


235 


leaking out as they would from the open-ended 
triangular type of package. The technique of 
manufacturing the short Chaff does not permit 
easy packaging in a triangular or cylindrical 
bundle. 


Flat Chaff 

The electrical theory for flat Chaff is iden- 
tical with that for bent Chaff. The distinction 
between the two rests chiefly in the technique 
of manufacture. Flat Chaff is almost universally 
cut from paper-backed aluminum foil. The use 
of paper instead of foil for the fundamental 
strength permits the use of much thinner foil, 
generally 0.00035 in. in thickness. Where the 
source of aluminum foil is limited, as was the 
case in the United Kingdom, the slight saving 
in foil may be worth while. Furthermore, flat 
Chaff is cut by guillotine-type paper cutters 
which are commonly available in almost all 
establishments that fabricate or use large quan- 
tities of paper. Production of flat Chaff can be 
carried out by any of these companies without 
special training of the already skilled guillotine 
operators; unskilled labor can do the work of 
packaging. 

The guillotine cuts flat Chaff from a stack 
of sheets of paper-backed aluminum foil. The 
width of each cut is controllable to approxi- 
mately %2 in., the precision being dependent 
upon the skill of the operator and the vintage 
of the guillotine. Widths less than approxi- 
mately Ys in. are difficult to control with a 
guillotine and widths of in. or more are 
considered desirable by members of the trade. 
Flat Chaff used by the Germans was aimed at 
a width of 2 cm but frequently deviated from 
this width by 50 per cent. 

The original flat Chaff, some 2 cm in width, 
was rather inefficient per unit weight because 
of tearing, birdnesting, and unnecessary width. 
During the fall and winter of 1943 the British 
adopted to some extent the production of Amer- 
ican-type Chaff and simultaneously set about 
improving their flat Chaff. Having established 
their production method on the basis of ma- 
chinery and techniques available in England, 
they found it more convenient to continue 


largely with their original type of production 
method. The use of narrdwer strips, of the order 
of %6-in. width, with more suitable paper 
backing, and a reduction in the number of 
strips from 2,000 to 500 per bundle resulted in 
a marked increase in efficiency of British flat 
Chaff. Large quantities of this flat Chaff were 
used by the American Air Forces in the United 
Kingdom when transportation difficulties led to 
shortages of American Chaff. 

The lower frequency range in which flat 
Chaff can be used is limited by the length of 
the standard guillotine cutters, 60 to 72 in., 
and, more vitally, by the problems of dispensing 
and birdnesting. A length of 70 in. corresponds 
to 80 me. The physical manipulation of Chaff 
strips of this length is obviously extremely 
difficult in an aircraft but can be carried out 
if necessary. The folding or bending of bundles 
of long Chaff results generally in serious tear- 
ing or in birdnesting. It may be concluded, 
therefore, that for special problems 80 me is 
approximately the lower limit for flat Chaff 
but that a more practical lower limit occurs 
around 150 me. Were no other type of Window 
possible for these low frequencies, flat Chaff 
could be utilized, but since Rope operates rather 
well in these ranges it is generally to be rec- 
ommended. 

At extremely high frequencies the greater 
width of flat Chaff reduces efficiency as com- 
pared to bent Chaff, although both the British 
and the U. S. Navies produced rather heavy 
types of flat Chaff usable against horizontal 
polarization in the 3,000-mc region. 

To summarize briefly, flat Chaff can be used 
conveniently in the frequency range from 150 
me to perhaps 5,000 me, and, although perhaps 
twice the weight and bulk of bent Chaff per 
unit over the same frequency band, it can be 
made with normally available equipment. The 
best developed type of British flat Chaff is 
slightly more economical in the use of alumi- 
num foil. Although comparative tests of flat 
Chaff against bent Chaff have not been ex- 
haustive, there are indications that the indi- 
vidual strips of flat Chaff are more effective 
than those of bent Chaff in a ratio of perhaps 
8 to 5. Probably a physical distortion in the air 
leaves a permanent bend in the aluminum 


236 


RADAR DECEPTION AND CONFUSION 


strip, whereas the paper-backed flat strip tends 
to recover because of its greater pliability. This 
characteristic, combined with the somewhat 
greater frequency band of response given by 
flat Chaff and the somewhat less birdnesting, 
tends partially to equalize the two types with 
regard to weight and volume per unit, leaving 
only the factor of two. Flat Chaff, however, 
drops 30 to 50 per cent faster than bent Chaff. 

Changes in humidity cause a marked curling 
effect in flat Chaff made from a sheet of alu- 
minum mounted on a single sheet of paper. To 
eliminate this curling effect, flat Chaff manu- 
factured for the U. S. Navy is designed as a 
sandwich of aluminum foil between two sheets 



Figure 6. Various types of U. S. Navy flat 
Chaff. 


of tissue paper. Humidity changes set up equal 
strains on the two sides of the individual strip 
and curling is reduced to negligible proportions. 
Aside from somewhat greater difficulties in 
manufacture because of extra lamination, this 
type of Chaff is superior to the flat Chaff made 
with only one sheet of paper. Humidity controls 
were very strictly observed in the production 
of British Window to reduce the curling phe- 
nomenon. It is possible that the very poor 
quality of paper used perforce by the British 
was largely responsible for the success of their 
flat Chaff. The paper was only one order better 
than our blotting paper, with so low a tensile 
strength that curling from humidity changes 
was greatly reduced. Test quantities of flat 
Chaff cut from American bond paper of normal 
quality performed badly. 

In the manufacture of flat Chaff, the U. S. 
Navy exploited a very practical method to pre- 
pare for unknown enemy radar frequencies in 
distant theaters of action. For this purpose 


their flat Chaff was cut in two standard lengths, 
20 in. and 60 in. The dipoles, however, were 
connected at both ends by the seal that was 
originally placed at the ends of the stack of 
sheets from which the dipoles were cut (Fig- 
ure 6). The handling of the Chaff stacks was 
expedited greatly by the seals but the Chaff 
could not be used until the ends of the packages 
were cut. In field operations, after the enemy 
frequencies had been ascertained by Ferret 
missions, small hand-operated guillotines were 
used to cut the Chaff (including the cardboard 
bundle) to length. These guillotines are simple 
in operation, can be easily sharpened, and a 
few of them are capable of cutting the ends 
from large quantities of Chaff. Contingencies 
with regard to enemy radar frequencies can be 
dealt with easily in the field without the com- 
plication of elaborate manufacturing plants. 
Such a Chaff procedure, useful to the U. S. Navy 
in the distant Pacific Theater where enemy fre- 
quencies could not be anticipated, would not 
have proved useful to the U. S. Army Air 
Forces in the European Theater of Operations, 
where extremely large quantities of Chaff were 
needed for a specific frequency band. 

It is of general interest that all types of 
paper-backed Chaff, both bent and flat, that are 
packed longitudinally in paper or cardboard 
bundles can be cut to shorter lengths by hand- 
operated guillotine machines without serious 
damage to the strip. In the case of Chaff made 
from pure aluminum without paper backing, 
a certain amount of welding occurs at the end 
where the cut is made and the birdnesting is 
somewhat increased. Nevertheless, it is gen- 
erally possible to cut Window to resonate at a 
higher frequency, without complicated equip- 
ment, in the field. 

British Window was almost universally pack- 
aged in a roll-type bundle. The U. S. Navy flat 
Chaff was packaged in a light cardboard wrap- 
per as shown in Figure 6. German flat Chaff, 
dimensions 2x80 cm, was held in bundles of 
several hundred strips by means of two sealed 
paper bands that break in the slip stream of 
an aircraft. Tearing and birdnesting from the 
German-type Window is quite excessive. There 
was also some question as to the formula used 
by the Germans in calculating the length of 



GENERAL DESCRIPTION OF WINDOW 


237 


the dipoles. Strips 80 cm long correspond to a 
frequency of approximately 177 me, not reso- 
nant with any of the British radars against 
which the Chaff was presumed to operate. The 
tearing was so great, however, that the Chaff 
resonated rather well at almost all higher fre- 
quencies, including the S band. It must be noted 
in this connection that such a method of obtain- 
ing wide-band response from Window is not 
economically sound, although it may occasion- 
ally be useful under the pressure of circum- 
stances. 

The physical awkwardness of 1-f fiat Chaff, 
especially for automatic dispensing, constituted 
a long-standing problem. In the spring of 1945, 
however, a solution was obtained which appears 
to offer promise. Flat Chaff was made for the 
182- to 212-mc band by using relatively heavy 
hard foil (0.0009 in.) backed on both sides with 
light paper (15-lb tissue). Three layers of 220 
strips %x 281/2 in. were each folded in the form 
of a foreshortened S (Figure 7). The birdnest- 
ing with this type of bent Chaff was only about 
20 per cent soon after the Chaff was packed. 
In about 10 weeks, however, the birdnesting 
increased from 20 to 35 per cent. Because of 
the end of World War II, further aging tests 
were not conducted. However, it is possible that 
the “set’’ of the paper might increase the bird- 
nesting still further and also reduce the effec- 
tiveness of the dispersed dipoles. 


Tuned Rope 

Although never produced in quantity for 
countermeasure purposes, tuned Rope^^^ may 
excel in two types of problems : 

1. Where it is desirable to maintain a re- 
flector for a long period of time, e.g., a balloon- 
supported reflector for meteorological purposes. 

2. Operation against a vertically polarized 
system over a frequency band too low for the 
efficient use of Chaff and too narrow to justify 
the heavier untuned Rope (see Section 12.2.6). 

At low frequencies and vertical polarization, 
tuned Rope theoretically should be much lighter 
per unit than untuned Rope or Chaff of the 
types already developed. Practically, however, 
no successful tuned Rope has been developed at 


low frequencies. A natural medium to support 
the dipoles is paper, which can be easily fabri- 
cated into neat compact rolls and unrolled auto- 
matically on release from an aircraft. An ex- 
ample of such a tuned Rope is shown in Figure 
8. The dipoles were glued to a continuous roll 
of paper in wide sheets of the correct length by 
the laminating machinery used in the foil in- 
dustry. The larger rolls were then slit into nar- 
row rolls, each of which was attached to a 
parachute-opening device. Drop tests from air- 
craft uncovered a fundamental difficulty that 
has not yet been solved for tuned Rope using 
a paper medium. The set of the paper in the 



Figure 7. Low-frequency Window packaged for 
mounting on double tapes for automatic dis- 
pensing. 


small roll causes the Rope to rewind into a 
compact tangle. The use of a heavy core might 
be practical against a system with only vertical 
polarization but would increase the rate of fall 
unduly. It is possible that a cellophane^" or, 
better, some similar thin supporting medium 
could be used instead of paper ; further experi- 
menting might prove fruitful in developing this 
type of tuned Rope. 

Theory indicates that the response per unit 
length of tuned Rope is not highly sensitive to 
the distance between the ends of the dipoles. A 
mass production method of breaking the elec- 
trical contact at suitable intervals along a con- 
tinuous roll of foil laminated to some medium, 
such as paper, might produce a very satisfac- 
tory type of tuned Rope even though the breaks 
are small compared to the length of dipoles. 

c Cellophane has proved to be unsatisfactory as a foil 
backing because of its elasticity and sensitivity to 
humidity changes. 


238 


RADAR DECEPTION AND CONFUSION 


With 0.00035 in. thick foil a 110-v current 
across contacts separated by a distance of the 
order of in. will burn off the foil without 
damaging the paper backing. This method is 
undoubtedly capable of development for mass 
production but has not been pursued because 
of the difficulties enumerated above in actual 
operation. The method, however, has been fur- 
ther developed for removing the metallic tinsel 
from the tinsel wire used as a flexible conductor 
in telephonic devices. 

Tinsel wire consists of a thin and narrow 
metallic ribbon wound spirally about a thread. 
When the thread is constructed of glass, the 
tensile strength is surprisingly great, sufficient 
to support a spool of several thousand feet. In 
the present fabrication of tuned Rope from 
tinsel wire, the metal of the wire is removed at 



Figure 8. Tuned Rope. 


intervals by passing the wire over a fixed pair 
of contact points which are electrified at uni- 
form intervals or by passing the wire over a 
wheel on which are located several properly 
spaced pairs of contact points. The use of an 
air blast to remove vaporized metal from the 
contact point has made the rotary-wheel system 
promising as a mass production device. 

If the tuned Rope made from tinsel (Tinsel 
Rope or Fishline) is to be used more than once, 
it can be run into a braiding machine or covered 
with a lacquer in order to prevent the glass 
thread from fraying. If the Fishline is to be 
used only once, as a countermeasures device, 
the sparked tinsel thread can be used directly 
(Figure 9) . 

Tinsel Rope tuned for the S band proved 
moderately successful when woven into a stand- 
ard target sleeve for use against an S-band 
gun-laying [GL] radar system. Development 
of the material as a reflector on meteorological 
balloons and possibly as a countermeasures 


device is incomplete but shows some promise. 
Tinsel Rope has the advantage of relatively 
light weight, extreme compactness, and sim- 
plicity of manufacture, once production ma- 
chinery has been developed. Its operational effi- 



I II III IV 

Figure 9. Tinsel (Fishline) Rope. I is tinsel 
before firing, II is tinsel after firing, III is fired 
tinsel covered by lacquer, and IV is fired tinsel 
covered by braiding. 

ciency, however, deserves much more thorough 
evaluation. It may be used at any point in the 
radar spectrum, conceivably to 30,000 me, but 
more probably to 10,000 me. 


Turnstiles 

A priori, thin wires might be expected to 
compete favorably with Chaff, particularly at 
higher frequencies where birdnesting might 
appear not to be serious. As a matter of fact, 
a few elementary calculations will show that 
wire in dimensions that are practical opera- 
tionally is both heavy and voluminous as com- 
pared to Chaff. An aluminum wire of diameter 
of only 0.010 in. corresponds in cross section 
to a foil strip 0.10 in. wide and 0.0008 in. thick. 
The wire has the added disadvantage of a rapid 
rate of descent and a much reduced bandwidth 
of frequency response. 

It becomes apparent, therefore, that wire is 
desirable as a form of Chaff only when a rapid 
fall is desired and when the weight of the 
single unit is not of great importance. Such a 
set of conditions arises when reflectors are to 



GENERAL DESCRIPTION OF WINDOW 


239 


be used in small quantities for identification or 
signaling purposes, for example, in ground- 
controlled approaches of aircraft where many 
aircraft are involved and where misidentifica- 
tion is apt to occur. An aircraft in radio com- 
munication with the control radar on the 
ground may, upon request, identify itself by 
dropping Window. Rapid-falling Window is ob- 
viously desired in order that clutter may not 



Figure 10. Turnstile. Wires are mutually at 

90°. 

interfere with the controlling radar. The 
method has been tried but not adopted for 
general use. 

In certain spoof operations a fast-dropping 
Chaff is desirable in order that the Chaff may 
drop quickly out of the radar lobe. A long 
formation of aircraft may thus be simulated. 
In this operation, however, the weight of wires 
and their narrow frequency band of response 
constitute a marked disadvantage. 

It has been reported that Turnstiles, made 
from three half-wave dipoles of wire held mutu- 
ally perpendicular at the centers, have been 
tested as reflectors on tow-targets and balloons 
with mediocre success. Turnstiles (Figure 10) 
are relatively difficult to manufacture, cannot 
be packaged compactly, and fall very rapidly. 


Their usefulness as a radar countermeasure 
appears to be exceedingly limited if, indeed, 
they can be used effectively at all. 


Rope 

Untuned Rope, as it has been produced in 
quantity, consists of rolls of 0.0009-in. foil 1/2 in. 
wide and 400 ft long (the British have used 
considerable quantities in 200-ft rolls). These 
rolls are roughly 3 in. in diameter and packaged 
three to a bundle. Two types of opening devices 
have been used, a small paper parachute or a 
simple card each attached to a 15-ft leader tape 
of rayon or cotton ribbon (Figure 11). The 
long leader strip was found necessary to insure 
that the card or parachute would remain at- 
tached to the foil streamer in the slip stream 
of an aircraft. 

Before opening tests had been conducted it 
was visualized that the streamer would hang 
vertically below the parachute after unrolling. 
This expectation was far from the truth. The 
forward motion of the foil roll first unwinds 
the streamer in a nearly horizontal position 
during the first seconds after the roll enters 
the slip stream. The roll then decelerates be- 
cause of the air resistance, finally unwinding 
in a downward direction. Both the parachute 
and the card are then apt to fall more rapidly 
than the central portion of the streamer so 
that in many instances the streamer appears 
as an inverted parabola approximately % to 
1 min after it opens. The curve of the streamer, 
however, is quite irregular and distorted. 

When a parachute is employed, the response 
in vertical polarization tends to be 2 or 3 db 
greater than in horizontal polarization. How- 
ever, when a core is used, the response is about 
equal in both polarizations. 

If the central core drops off, the streamer is 
much more irregular than if the core remains 
attached. The streamer with a detached core 
tends to tangle and bunch at the lower end; 
radar tests indicate that a slightly greater hori- 
zontal component of reflection occurs in this 
instance than when the core remains attached. 
Cores have generally remained attached be- 
cause the rolling process of manufacturing is 


240 


RADAR DECEPTION AND CONFUSION 



Figure llA. Untuned Rope for use against 
frequencies below 350 me. Two types of opening 
devices are shown, a small paper parachute and 
a simple card. 



Figure IIB. Untuned rope for use against fre- 
quencies below 350 me, here shown packaged. 


simplified by gluing the foil to the core. The 
operational difference between the two types is 
small. More recent tests have shown that simple 
foil rolls without leader strip, cards, or inner 
sleeves are nearly as effective against 100-mc 
horizontal polarization as is standard Rope. 
More complete testing is needed, however, to 
demonstrate without a doubt that such a change 
is justified. The simplification in manufacture 
would be considerable and justifies much more 
testing in case large quantities of Rope are to 
be produced. Some gain in response could be 
obtained by insuring that the core of the roll 
will fall off the streamer. It is important that 
the optimum balance between manufacturing 
cost and performance be attained before estab- 
lishing specifications of Rope. 

A reduction in the width of Rope to % in. 
and a reduction in thickness to 0.0006 in. show 
a theoretical factor of gain of 2 in weight and 
value. Practically, however, the theoretical gain 
of 500 was attained at 200 me on horizontal 
polarization but not at 100 me. As a conse- 
quence, it appears likely that minor production 
improvements in Rope may be more 

economical than a change to l^-in. Rope. 

The response characteristics for Rope have 
been measured empirically from about 75 me 
up through the S band. The theory of the re- 
sponse is complex, but a first approximation 
indicates that a bundle of Rope equals approxi- 
mately one unit at 200 me, responds with in- 
creasing efficiency at lower frequencies, and 
tapers off in effect at higher frequencies. At 
200 me, in the Wurzburg band and in the 
S band, the theory is rather well confirmed by 
observations. The response at 3,000 me from a 
bundle of Rope is roughly one-fifth of a unit. 
The frequency band of maximum efficiency for 
Rope is known to lie in the region from about 
75 me to perhaps 300 me and the lower limit 
may be well below 75 me. At frequencies above 
300 me. Rope may still be used with consider- 
able effect but its efficiency decreases fairly 
rapidly with increasing frequency. Under spe- 
cific operational circumstances, the questions 
of quantity of Window needed, methods of 
transport, and dispensing techniques determine 
the choice of which type of reflector should be 
used. 



GENERAL DESCRIPTION OF WINDOW 


241 


^ ^ Corner Reflectors 

Three mutually perpendicular planes inter- 
secting at a point constitute a corner reflec- 
tor46i. 150 if the planes are electrical conductors. 
Wire mesh can be used as the reflecting planes 
for wavelengths considerably greater than the 
dimensions of the mesh. Qualitatively, radiation 
is reflected successively from the three planes 
back in the original direction, as a handball 
returns from the corner of a handball court 



Figure 12. Principle of corner reflector. 


(Figure 12). More refined theory shows that 
the effective echoing area of an ideal corner 
reflector varies as where d is the length 

from a corner along an edge, A, is the wave- 
length, and the ratio d/X is large. Hence, the 
effective area of a given corner reflector varies 
as the square of the frequency ; at a given fre- 
quency, a given type of corner reflector has an 
effective area proportional to the fourth power 
of its linear dimensions. 

A second theoretical conclusion turns out to 
be of primary practical importance. If the 
angles formed by the three surfaces forming a 
corner deviate from 90 degrees, the equivalent 
echoing area is reduced. If the error at the tip 
of each of the three arms is 0.35X, the response 
will be decreased 3 db. If it is 0.62X, a loss of 


10 db results. Thus, at 10,000 me (wavelength 
of 3 cm) deviations of tihe outer edges of the 
three surfaces of about 2 cm (0.62 X 3 = 1.86) 
will reduce the equivalent echoing area by about 
10 db. 

To assess the significance of these theoretical 
deductions in the practical problems of corner 
reflectors, the specific use and concomitant me- 
chanical design of the corner reflector must be 
considered. Five classes may suffice : 

1. Airborne, self-opening, and free-falling 
(Kites) to be used as countermeasures. 

2. Balloon-supported for countermeasures or 
meteorology. 

3. Aircraft-towed as radar GL targets. 

4. Raft- or boat-supported. 

5. Ground-based. 

Airborne, self-opening, and free-falling cor- 
ner reflectors were earlier known as Angels and 
later as Kites. A great amount of effort has 
been expended in their development. A late 



Figure 13. Seventeen-inch self-opening Kite 
(Angel) packaged for dispensing from an air- 
plane. 


example is shown in Figure 13. The four-quad- 
rant type is sufficient because reflection below 
the fundamental plane is usually satisfactory 
for the purposes of countermeasures. Required 
characteristics are light weight, compactness, 
reliability of opening, strength to withstand 
the shock of opening, ability to orient properly 
in the air, and, last (and most difficult), main- 
tenance of angular tolerances while falling 
freely. 



242 


RADAR DECEPTION AND CONFUSION 


The principles of the best design for Kites 
can be seen by inspection of Figure 13. Upon 
the opening of an outer bundle, a central spring 
raises the arms, which then support the lac- 
quered foil surfaces. The Kite floats down 
slowly, acting as its own parachute. All of the 
required characteristics were attained with 
reasonable success except for the maintenance 
of angular tolerances in the air. The most care- 
fully made examples failed by about 10 db in 
returning the theoretical radar response. 

Kites must be designed so that they may be 
handled conveniently in aircraft. A package 
length of 3 ft is about the maximum dimension 
of package which can be tolerated ; this fixes the 



Figure 14. Mesh corner reflector for use on a 
life raft. 


maximum dimensions of practical Kite at about 
6 ft. This size Kite should give a unit echo at 
frequencies in the neighborhood of 3,000 me. 

Development of a 3-ft Kite was first under 
taken but later abandoned because of operating 
difficulties, bulkiness, and weight. Experience 
gained from the work on larger Kites was then 
applied to the development of 17-in. one-half 
diagonal Kites to operate at 10,000 me and 
higher frequencies. The best models failed in 
radar response by 10 db, as mentioned above. 
Whether the failure arose largely from the 
bowing of the foil surfaces during descent, or 


from the lack of squareness, could not be deter- 
mined with certainty. A supporting parachute 
for this type of Kite was found to be imprac- 
tical, because of the bowing of the horizontal 
surfaces and because of the fact that the para- 
chute would collapse on top of the Kite because 
of the slow rate of descent. A parachute might 
be employed profitably, however, if some type 
of wire mesh could be substituted for the foil 



surfaces, but further research on the problem 
appears to be of doubtful value. 

Balloon-supported corner reflectors present 
fewer complications in design than the self- 
opening free-falling varieties. Four-foot half- 
diagonal Kites have been used by the United 
States Navy on balloons attached to unmoored 
rafts. Corner reflectors carried by free balloons 
were partially successful for meteorological 
purposes when used in conjunction with S-band 
radar systems. Long periods of fadeout intro- 


GENERAL DESCRIPTION OF WINDOW 


243 


duced serious difficulties, as did low response 
at great distances. 

The problem of maintaining angular toler- 
ances in a lightweight reflector is the most 
serious one for balloon-supported corner re- 
flectors. This problem must be solved if the 
response characteristics of a corner reflector 
are to be satisfactory for radar tracking. 


covered with wire mesh, and fabric sleeves 
covered with Tinsel Rope proved less effective. 
At the crossover point, as seen from the radar, 
the radar tends to follow the tow-target cable 
— with consequent danger to the towing air- 
craft. It is hoped that low-reflection tow-target 
cable^^^ will materially assist in this problem. 

Raft- or boat-supported corner reflectors for 




ImUfesUh 

Oit Angri«« dtf ftoyiJ Air Foret auf ^gtsthfand «nd nur d«r 
erste Abschnitt der briliscK-amtrikanischto Offtfisiw. An d«r 
Vorbtreitung dts jwtittn arbttten England urgj Amtrika Tag 


und Nacht. 


ImOsUn 

Di« trsten neun Honate des Russtnkriegs babtn Deutschland 
mehf Blut gekostet ais die vier |ahre des ersten Weltkriegs. 
Wieviel Blut werden die iweiten neun Monate Deutschland 
kosten ? Die ganze Welt weiss, da$s Deutschland den Krieg am 
Ende vertieren muss. 

Kann dieses Gemetzel beendigt 
werden, ehe es zu spat ist? 

Moth einmal hat die brttische Regicrung durch die 
Erklarung lord Cranbornes vom 21. Mai und die Sonder- 
botschaft von Sir Stafford Cripps vom II. Mai den Weg 
hierzu klar und deutiich gezeigt. 

• DIE OEUTSCHEH mussen den Krieg, den Hitler urn 
Jahre lu verlangern trachtet, selbst verkiirzen. 

• DIE OEUTSCHEH mussen die Herrschaft einer Gang- 
sterbande, die Hitler und seine Spiessgesellen 
Deutschland auferlegt haben, selbst sturzen. 

• DIE DEUTSCHEN mussen sich an die Seite der unter- 
druckten Vbiker stellcn, die alle fur die Wiederer- 
richtung ihres Staates kampfen, eines Staates, der 
auf der Achtung vor den Rechten der Vbiker und 
des Einzelnen beruht. 

Die umstehend wiedergegebenen Erklarungen sind ebenso wie 
^ ahniitben Erklarungen britischer Staatsmanner von der 
Hkkrregierung demdeutschenVolkentweder ganz unterschlagen 
in eerzerrter Form mitgeteilt worden. 


NACH 

HITLERS STURZ 


Uber die britische Nachkriegspoiitik gegeniiber Deutsch- 
land hat lord Cranborne am 21. Mai 1942 fur die 
britische Regterung folgende Erklarung abgegeben : 

E ines der Zliele. flif die wjr in diesem Kneg kampfen, heis$t 
GenechligkcU. Gercchtigkcii ruerst fur die son Deutschland 
verskiavten Volker, Gerechtigkeit fur uns selbst. Oerechtigkeit 
fur Deutschland, und hartc. unbeugsame Gerechtigkeit fiir jene Deuiscben, 
die sich der abscbculichen Verbrcchen schuldig gemacht haben, dcren 
Zeugen scir waren, 

..Die Nazifiihrer kbnnen wir nur als Gangsters betrachten. Auf ihr 
Wort ist kern Vcrlass. Unsagbarc Verbrcchen haben ihre Hlnde besudelt 
Solange die Nazifuhrer in Deolschiand an der Macht sind, so iange gibt 
cs ftir Europa weder Frieden noch Gertxbtigkeit. 

..Die nach dem vorigen Krieg vcrfolgte Politik ist nicht die Politik, 
wte sie die Churchill Roosevelt Erklarung festgeiegt hat. Die Politik 
nach dem vongen Krieg flihrtc, (wenn auch nicht mit voller AbsiebtK 
zu Deulschlands wirtschaftlichcr und. militariscber Bestrafung, Vbllig 
andere Auffassungen leitcn die Churchill Roosevelt Erkldrung, Aus 
thr spricht die feste Entschlossenheit zu verhindern, dass Deutschland 
Oder irgend ein andercr Angreiferstaat jemah wieder imsiande ist, cine 
neue Weltkatastrophe hcraufzubeschwdren. Es besteht aber keineswegs 
die Absicht, Deutschland wirtschaftlkh zu bcnachtcjligen." 

Was dies vom deutschen Volk verlangt, hat Sir Stafford 
Cripps in einer Sonderbotschaft an Deutschland fiber 
den londoner Rundfunk am 11. Mai 1942 klargemacht: 

H itler gewann seine ersten Siege in Deutschland selbst - gegen 
die Gcwerkschaftert. gegen die Kia-hen. gegen das deutsche 
Volk. In Deutschland begann dieser Weltfcricg und in 
Deutschland muss cr beendet werden . . . W'ir sind alle Soldaten einer 
gfossen Armee der Freibeit, die alle Lender umfasst. Die einen (ragen 
Walfen — die besten Waffen der Weh. Die anderen sind unbewaffnei, 
Abcr jeder kann handeln. jeder kann zuschlagcn — fiir den Sieg. Keiner 
kann neutral bleiben. Jeder muss durch seine Taten zeigen. wo cr stehf. 
ob gegen uns und die Freihcit. Oder an unserer Seite in der grossen Atmee 
der werdenden W'elt." ^ 


Figure 16. Earliest type of British window. 


Heavier corner reflectors have been built by the 
United States Navy to maintain angular toler- 
ances, but they require excessively large bal- 
loons. 

Aircraft tow-target sleeves have incorpo- 
rated corner reflectors for radar GL practice. 
Wire-mesh corners have proved to be the most 
successful type of reflector for the purpose in 
the S and X bands. Turnstiles, fabric sleeves 


countermeasures, for position marking, or for 
GL targets, must be relatively large to be 
effective. The problems are generally outside 
the province of this book and will not be dis- 
cussed in detail. A mesh of noncorrosive metal 
is most commonly used. The supporting frame- 
work becomes a marine construction problem. 

An eight-quadrant collapsible corner re- 
flector designed for life rafts in air-sea rescue 


244 


RADAR DECEPTION AND CONFUSION 


work has been manufactured in quantity. It 
is beautifully designed with monel mesh on 
a Duralumin frame and die-cast central fitting 
(Figure 14). Reports suggest, however, that it 
may be too small to be observed in the S band 
at a sufficient distance. The half-diagonals are 
21 in. 

Ground-based corner reflectors can be made 
with the precision required, since weight is of 
minor importance. Surprisingly large dimen- 
sions are required, however, to simulate cities 
or groups of buildings for airborne radar de- 
ception. Buildings constitute corner reflectors 
in themselves and as such can be simulated only 
by corner reflectors of nearly comparable 
dimensions. 

Reflectors used as ground markers usually 
must be rather large to show through the 
ground clutter. 

Diplanes, constructed from two mutually per- 
pendicular planes of conducting material (Fig- 
ure 15), are essentially a special case of the 
corner reflector. They can be substituted for 
corner reflectors where all angles of radar ob- 
servation lie nearly in a plane. A typical situa- 
tion is that of a balloon-supported corner 
reflector to be observed only at long range and 
consequent low angle of elevation. Here a 
diplane hung with its axis vertical would be 
quite as satisfactory and much simpler in con- 
struction. 

All problems involving corner reflectors 
should be investigated carefully for the pos- 
sible substitution of diplanes. 


^ ® Squares or Sheets 

Sheets of paper-backed foil were the first 
form of Window to be tested by the British. 
Rectangular sheets were printed for psycho- 
logical purposes (Figure 16) in addition to 
their countermeasures value. None was actually 
used, however, because of security reasons. It 
was feared that the enemy would retaliate with 
Window and seriously weaken the then vulner- 
able United Kingdom radar chains. Simulta- 
neously, the Germans kept Window completely 
hidden for the analogous reason. 

Sheets of foil ^^7 (Jq ^ot resonate but act 


only as mirrors for wavelengths smaller than 
twice the length of the sheet and as poor 
scatterers for greater wavelengths. Hence, 
dipoles are more efficient than sheets by orders 
of magnitude for frequencies up to approxi- 
mately 10,000 me. As Window theory developed, 
the British quickly abandoned the large sheets 
for use against the German Wurzburg fre- 
quency and developed flat Chaff, which they 
first used in July 1943. 



Figure 17. RR 12/U Window for use in both 
polarizations against frequencies above 8,000 
me. 


For all frequencies above about 10,000 me 
small squares of paper-backed foil (Figure 17) 
constitute a fairly satisfactory form of con- 
fusion reflector. The weight per unit runs high, 
around the two-lb level, but a single bundle 
covers the entire higher-frequency spectrum up 
through the heat region and into the visual. 
The bulk is not unusually great. The squares 
are cut by guillotine. The response is essen- 
tially independent of polarization. 


Other Considerations regarding 
Window Operations 

The foregoing discussion on the theory and 
application of reflectors to radar deception and 
confusion is by no means complete. For ex- 
ample, no mention has been made of the use of 
this type of material in mortar shells or rockets 
for front-line identification purposes. No dis- 



ELECTRICAL CONFUSION AND DECEPTION METHODS 


245 


cussion has been given of the development of 
methods for identification of Window echoes 
as differentiated from actual target echoes. No 
discussion of automatic dispensing is included, 
which, although a purely mechanical problem, 
affects the usefulness of this material very 
greatly. Finally, the operational phases of the 
problem have been touched upon only briefly. 
All these matters are discussed in some detail 
in a special report summarizing the work 
which has been done in this field,^^^ which in 
turn refers to the original reports on the vari- 
ous phases of the activity. The above discussion, 
then, is designed only to give the reader an 
orientation in the field and to indicate its scope. 


12.2.10 ^ Study of Persistent Echoes from 
Shell Bursts 

Work was undertaken rather early with the 
object of discovering, and, if possible, con- 
trolling the mechanism or reflection associated 
with the persistent radar echoes from shell 
bursts. Preliminary measurements were made 
on conductivities of burning gases and of gases 
in contact with burning matter and on the 
effects of such gases on propagation in wave 
guides. These experiments showed that the 
conductivities involved were generally so low 
that no strong reflections of radar signals from 
the hot gases in an explosion should be ex- 
pected. Actual shell bursts were then observed 
at the Aberdeen Proving Ground with a track- 
ing radar. The echoes were found definitely to 
be due to the falling shell fragments and not 
to the hot gases, which do not fall but expand 
rapidly and in this case were quickly blown 
to one side by the wind. Confirmatory experi- 
ments were performed in collaboration with the 
Radiation Laboratory on radar echoes from 
quantities of nails dropped from aircraft. It 
was concluded that echoes from the hot gases 
in shell bursts would not be strong enough 
to be of any use in confusing enemy radars. 
In the preliminary experiments, striking effects 
were observed with burning phosphorus and 
experiments on phosphorus-loaded shells were 
proposed. These experiments were never car- 
ried out because the advent of Window yielded 


a simpler and satisfactory solution of the 
problem. \ 

12 3 ELECTRICAL CONFUSION AND 
DECEPTION METHODS 

Electrical confusion and deception devices 
offer interesting possibilities for counter- 
measures applications. The possibility of trans- 
mitting false signals on the enemy frequency 
occupied an appreciable fraction of the research 
and developmental time of Division 15, and, 
although none of the devices was carried past 
the simulated operational stage, they were 
ready and might have been used under some- 
what different tactical situations. 

Actually, three main lines of investigation 
were carried out in the electrical deception and 
confusion field. One of these, involving trans- 
mission of deception signals for early-warning 
[EW] radar, was actually used operationally 
with considerable success by the British. Serv- 
ice laboratories in this country did some work 
on these so-called Moonshine methods, and 
interesting results were obtained, but it is 
beyond the scope of this volume to describe 
such activities. Another type of electrical decep- 
tion and confusion device upon which Division 
15 did considerable work was the so-called 
Peter system, which (unlike Moonshine) was 
intended to confuse the direction, but not the 
range, of the target carrying the equipment. 
Finally, some attention was given to the vari- 
ous possibilities presented by the use of ordi- 
nary jamming transmitters in conducting 
electrical deception operations, and by the use 
of other manipulating means for deceiving and 
confusing enemy radar. 


12 . 3.1 Electrical Pulse Repeater (Peter) 

The basic element of the Peter system^^® is 
an r-f repeater unit located on a ship or aircraft 
which is a target for enemy radar. This unit 
picks up the enemy radar signal, amplifies it, 
superposes modulation (if desired), and re- 
radiates the signal in the direction of the enemy 
radar. Unlike Moonshine, Peter reradiates only 


246 


RADAR DECEPTION AND CONFUSION 


a single signal for each signal picked up and 
so causes no error in range indication. 

The Peter unit makes possible at least three 
different procedures for confusing the enemy 
radar. 

1. If the enemy radar is a tracking set using 
conical scan or lobe switching, the reradiated 
signal can be modulated by a periodic function 
synchronized with, and phased with respect to, 
the radar lobing rate. This will have the effect 
of producing a fixed error in direction to the 
enemy radar. The error can be as great as 
about 40 per cent of the total radar beamwidth. 
This technique has the additional advantage 



6 

Figure 18. Type E and Type F of Peter sys- 
tems. 


that the radar operator will not be aware that 
the operation of this set is not normal. The 
final system of this type is referred to as the 
Type E Peter system. 

2. A second type of Peter system, known 
as Type F, also effective against conical scan 
or lobe-switched tracking radars, modulates 
the reradiated signal with a random wave con- 
taining components uniformly distributed in a 
narrow band bracketing the radar lobing rate. 
This system avoids the necessity for monitor- 
ing and synchronizing with the incoming signal. 
The effect produced is no longer a fixed deflec- 
tion of the radar but a random fluctuation of 


the apparent bearing which results in a “zone 
of uncertainty’" which will amount to about 
25 per cent of the total radar beamwidth. 

3. The Peter amplifier can be used against 
any radar to increase the strength of the signal 
returned to the radar and so to increase the 
apparent reflecting area of the vessel bearing 
the Peter ^system. Thus a small boat can be 
made to look to a radar like a destroyer or a 
light cruiser. A similar procedure can be em- 
ployed against radio-operated proximity fuzes, 
which detonate when a reflected signal from 
a target reaches a predetermined strength. Use 
of the Peter amplifier on the target will 
detonate the fuze when the projectile is still 
a safe distance away. 

The greater part of the Peter development 
has been in the 500- to 700-mc range. The most 
satisfactory amplifier for this range is the 
parallel-plane (lighthouse-type) triode using a 
grounded grid circuit in a coaxial tuner.^^^’ 
The amplifiers tested have usually included 
four to six such stages. When modulation is 
introduced it is applied to the penultimate 
stage. Block diagrams of Type E and Type F 
Peter systems are presented in Figure 18. 

During operation it would be troublesome to 
tune the amplifier to the frequency of an enemy 
radar. Also it would be desirable to use a 
system capable of operating against several 
radars at once. Hence, a considerable amount of 
effort has been devoted to making the Peter sys- 
tem cover a very wide frequency band. Single- 
channel amplifiers having bandwidths of about 
25 me and voltage gains of 3 per stage have been 
built using L-14 tubes. 

To achieve an extremely wide band, Peter 
amplifiers, each covering a fairly wide band, 
have been paralleled to form a multichannel re- 
ceiver. The problem of the choice in multi- 
channel amplifiers of the channel bandwidth 
and stage gain which will involve the smallest 
total number of stages to cover a given fre- 
quency band has been studied. The important 
conclusion emerges that the optimum stage 
gain is approximately 1.65, a conclusion which 
has served as a guide in the design of multi- 
channel Peter systems. With standard GL-446 
lighthouse tubes, channel bandwidths of the 
order of 20 me are consistent with this choice 


ELECTRICAL CONFUSION AND DECEPTION METHODS 


247 


of stage gain. With the L-14 tube, bandwidths 
of over 100 me should be obtainable. 

It was feared initially that trouble might 
be experienced because of coupling between 
receiving and transmitting antennas. With 
reasonable antenna separations and orienta- 
tions, no such difficulty has been encountered. 
With the two antennas mounted 25 ft apart 
with their axes parallel, the direct antenna-to- 
antenna signal is attenuated by more than 75 
db at 550 me. 

The time delay in the Peter amplifier is of 
the order of 0.2 psec, with the result that the 
return signal is actually superposed on the 
normal echo received at the enemy radar. 

Several novel modulation procedures have 
been evolved to avoid the necessity for manual 
monitoring of the received signals and to pro- 
vide accurate repetition of the received radar 
signal. A repeating modulator particularly for 
use in the Type E system against lobe-switched 
radars like the FD has been developed. In this 
modulator a perfect integration of the incoming 
signal is achieved without phase shift or time 
delay. The modulator for the Type F Peter 
system presented a difficult problem which was 
solved by playing back photoelectrically a 
sound track on which a sine wave whose fre- 
quency varied from 22.5 to 27.5 c had been 
recorded 100 times with random initial phase. 
This playback yielded a signal which ap- 
proached noise very closely and which included 
only the desired frequency components. 

An experimental Peter system has been built 
for operation at 3,000 me. Satisfactory per- 
formance was achieved in a three-stage ampli- 
fier using L-14 tubes. 

A system operating on the Peter principle 
has been constructed for operation in a 20-mc 
band around 125 me for use against proximity 
fuzes. In this set the signal is heterodyned to 
a video frequency, amplified, and reconverted 
to the original frequency in a high-level con- 
verter. 

The Peter system has had the following field 
tests : 

1. A Type E Peter set mounted on a 75-ft 
launch and used against an aircraft homing 
with an ASB radar^^s caused the aircraft to 
miss on homing runs by 800 to 2,500 ft. 


2. A Type E Peter set flown against an FD 
radar caused tracking errors of 4 to 6 degrees 
compared with normal tracking errors of 1 
degree. 

3. A Type E Peter used against a synthetic 
Giant Wurzburg produced an error of 1.6 
degrees. 

4. A Type F Peter used against a synthetic 
Giant Wurzburg produced a zone of confusion 
of 1.0 degree. 

5. A Peter system used as a straight r-f 
repeater against a Small Wurzburg and an 
RAF Type 11 search set gave an intensified 
echo equivalent to that of a destroyer. 

6. The 125-mc Peter system has been tested 
against proximity fuzes at the Airborne In- 
struments Laboratory with satisfactory results. 


12.3.2 Electrical Radar Deception 

Devices 

Ordinary jammers may be used in conducting 
electrical deception operations. An amount of 
care in planning such a movement equal to that 
shown in planning the use of jammers to cover 
the real attack must be shown or the deception 
will not succeed. 

If a bona fide raid is going to have certain 
radar countermeasures protection provided by 
Window and jammers, then it is possible to 
create a diversionary raid by using a small 
number of airplanes employing the same Win- 
dow and jammers in such a way as to create 
an indication on the enemy’s radar defense 
system which will duplicate that of the genuine 
raid. 

The prime requirement in carrying out any 
deception is that no element of the system being 
deceived shall be able to see through the decep- 
tion. Thus, countermeasures must be success- 
fully applied to all the elements of an enemy 
radar system and other methods of detection 
by the deception flight if it is to succeed. 

A possible deception technique that should 
be borne in mind is the use of pulse transmit- 
ters operating in the radar frequency bands. 
To a search receiver these transmitters would 
appear to be radar systems. It would be im- 
possible to determine with certainty which 


248 


RADAR DECEPTION AND CONFUSION 


emissions are actually from radars and should 
be jammed. Hence, if this method were prac- 
ticed on a large scale, by measures against all 
the transmissions, a considerable amount of 
RCM equipment would be required. 

A disadvantage that might result from the 
inauguration of this type of deception is the 
possibility that it will stimulate the acquisition 
and use by the enemy of jamming equipment 
for a large portion of the radar band of 
frequencies. Under such circumstances the 
frequencies that would be available for new 
radar equipment would be severely limited 
since the enemy would be prepared to jam over 
a good deal of the spectrum. 

A subterfuge that may be practiced and is 
almost certain to cause both confusion and 
deception until detected is the operation of 
radar equipment on the same frequency as that 
of the enemy but with slightly different pulse- 
repetition frequencies. This would be almost 


perfect insurance against jamming unless the 
enemy were also willing to forego the use of 
his equipment operating on the same frequency. 
By the same token, operation on enemy radar 
frequencies is feasible only if it is more im- 
portant to use our own radar than to deny the 
enemy the use of his by jamming. 

On the other hand, one should always be 
alert to the possibility that the enemy may set 
up a radar system operating in the same fre- 
quencies as our own equipment. In a theater 
where a number of radar sets are in use it 
is common to experience interference from 
the other units. Since these emissions are not 
generally synchronized with one another, any 
given radar can successfully concentrate on its 
own signals and ignore those of other radars 
as they pass across the screen. It is well to 
ascertain, periodically, that all such interfer- 
ing signals originate from one's own radar 
equipment. 


Chapter 13 

/ 

RADAR ANTIJAMMING STUDIES AND TRAINING 


13.1 INTRODUCTION 

T he overall purpose of the radar anti- 
jamming [AJ] program was to improve 
the performance of friendly radar systems in 
the presence of enemy offensive counter- 
measures. The program, therefore, included AJ 
training of operators as well as laboratory and 
field studies. 

Because this program was concerned not only 
with jamming and AJ modifications to radars 
but also with fundamentals of radar design 
and operation, AJ research and development 
work was done under the auspices of Division 
14 as well as Division 15. The latter phase 
of the program was carried out chiefly by the 
Radio Research Laboratory [RRL] of Harvard 
University (under contract OEMsr-411) ; the 
Division 14 work was performed mainly at the 
Radiation Laboratory [RL] of the Massa- 
chusetts Institute of Technology. In addition, 
several Service laboratories did AJ research. 
The large number of groups interested in the 
AJ program necessitated good liaison, which 
was successfully accomplished; especially close 
contact was maintained between Radio Re- 
search Laboratory and Radiation Laboratory. 

Although this chapter deals primarily with 
the Division 15 aspects of the radar AJ pro- 
gram, the relationship of this work to that of 
the other groups is considered to some extent 
also. Moreover, much of the AJ research in 
nonradar fields, especially in communications, 
is applicable at least in part to radar AJ also, 
and vice versa; this is particularly true, of 
course, of the more fundamental phases. The 
AJ work in communications and other non- 
radar fields is discussed in Chapter 9 of this 
report. The theoretical aspects of AJ are con- 
sidered in Chapter 6. 

Much of the AJ program was in the nature 
of insurance. The offensive jamming of the 
enemy in general was not very extensive or 
effective, but it was necessary to be prepared 
for serious enemy counteraction. Such insur- 
ance measures included both retroactive modi- 


fications designed to improve the performance 
of existing radars and improved AJ design 
features for new sets. 

The radar AJ effort of Division 15 is dis- 
cussed below under the following headings: 
(1) Laboratory studies, consulting, and com- 
mittee activities concerned with the develop- 
ment and application of good basic AJ design 
for radars. (2) Fundamental AJ studies, in- 
cluding research on basic AJ techniques and 
circuits, and basic laboratory studies on the 
relative effectiveness of various jamming sig- 
nals. (The latter especially have yielded infor- 
mation of importance to the offensive counter- 
measures program as well as to the AJ effort.) 
(3) Investigations of specific radar equipments, 
including both studies of the jamming suscepti- 
bilities of U. S. radars and navigation systems, 
and the engineering of retroactive AJ modifi- 
cations for radars already in the field. (4) The 
AJ training programs and the training 
apparatus used in them. 

Many phases of the radar AJ work are 
summarized below. From the start, however, 
emphasis should be given to the most important 
conclusion reached : that good basic design and 
good operator training are the most important 
AJ measures for the protection of radars. 


13 2 AJ DESIGN OF RADARS 

During the course of the work on jamming 
susceptibility and basic AJ techniques (de- 
scribed below), it became apparent that the 
use of special tricks and “black boxes'' as 
attachments to radar was in general much less 
effective against jamming than the application 
of sound engineering principles to the design 
of the radar. This conclusion is borne out by 
the fact that nearly all of the retroactive AJ 
modifications developed serve mainly to cor- 
rect faults in the original design of the equip- 
ment, although it is true that several specialized 
circuits have proved useful against special 
types of jamming encountered operationally. 


249 


250 


RADAR ANTIJAMMING STUDIES AND TRAINING 


Therefore, one of the prime objectives of 
the AJ program was to facilitate the incorpora- 
tion of sound AJ engineering principles into the 
design of radar equipments. Since Division 15 
was not itself a radar development agency, 
this function was accomplished by helping to 
make available to such agencies all possible 
data on AJ engineering practices and by cam- 
paigning actively for the inclusion of these 
practices in radar specifications and designs. 
The methods of furthering these aims can be 
described in two main categories: 

1. Representation on Office of Scientific 
Research and Development [OSRD] and 
Service AJ committees. 

2. Consulting services furnished to radar 
designers and manufacturers and to the Armed 
Services. 


13.2.1 Committee Activity 

By early 1943, the laboratory work on radar 
vulnerability and basic AJ techniques had 
reached the stage where it was most desirable 
that the AJ information be made available to 
the designers and manufacturers of radar 
equipments, since security regulations had until 
then prevented the dissemination of these data 
to agencies other than OSRD and Service 
laboratories. Accordingly, under the sponsor- 
ship of Division 15, an AJ Committee was 
formed in March 1943. Radio Research Labora- 
tory was represented on this committee by 
several members of the AJ Division of the 
laboratory; other members represented Divi- 
sion 14 of the National Defense Research 
Committee, the War and Navy Departments, 
Army and Navy Service laboratories, and each 
major manufacturer of radar equipment. The 
function of the AJ Committee was to facilitate 
the interchange of AJ information among 
laboratories and manufacturers and to con- 
sider how the information could best be inte- 
grated into radar design. The initial activity 
was primarily technical, and over a period of 
several months papers were presented on the 
details and performance of a number of AJ 
circuits and on principles of good engineering 


practice. A few months after the committee 
commenced its activities, a survey was initiated 
among the manufacturers of radar equipment 
to determine to what extent AJ features and 
engineering were being included in new radar 
designs. The incomplete results of this survey 
led to the recognition of the great need for a 
compilation of the basic principles of good AJ 
practice, to be used by radar designers and 
manufacturers and by the Service personnel 
engaged in formulating military characteristics 
and specifications for radar equipments; for 
it was realized that AJ features would not be 
included in radar designs unless the specifica- 
tions required it and unless the designers had 
the AJ information available. 

This compilation of basic AJ design features 
was undertaken by the AJ Practices Panel, 
consisting of representatives from Radio Re- 
search Laboratory, Radiation Laboratory, 
Service laboratories, and the Army. A thorough 
survey was made of the field to be covered, 
which showed that considerably more labora- 
tory work was necessary to present a complete 
summary of good AJ engineering practices. 
The work was allocated among the various 
research laboratories represented, and papers 
were written on their respective results. 

The Division 15 AJ Committee, not being a 
Service organization, could go no further than 
to recommend that AJ features be included in 
radar equipments. This fact was recognized by 
the Service members of the committee, and in 
early 1945 the AJ Working Subcommittee of 
the Joint Countermeasures Committee was 
formed, with an RRL member included. This 
committee attacked the problem of using official 
channels to obtain the incorporation of AJ 
engineering in radar design. It recommended 
that satisfactory AJ performance be specified 
as a military characteristic and that the in- 
clusion of AJ engineering in radar gear be 
the responsibility of the radar design agency 
as an integral part of development and pro- 
duction specifications. The committee prepared 
a comprehensive catalog of AJ devices and 
techniques. 

It is to be hoped that the work of these 
committees and panels will enable future elec- 
tronic equipment utilizing space radiation to 


FUNDAMENTAL AJ STUDIES 


251 


be designed with the principles of sound AJ 
engineering in mind. 


^ ^ AJ Consulting Activity 

To supplement the committee activities, con- 
sulting service was supplied to the Army and 
Navy on various occasions. This took the form 
of advising the Service laboratories or manu- 
facturers regarding the inclusion of AJ engi- 
neering in new equipment designs, of assisting 
the Armed Services in formulating specifica- 
tions for radar equipments to include AJ 
requirements, and of assisting in the prepara- 
tion of AJ training publications and films (see 
Section 13.5). 

On a number of occasions, AJ representatives 
were requested to sit in on early design con- 
ferences for new radar equipments. The basic 
principles of good AJ engineering were ex- 
plained for the guidance of the design engineers 
in avoiding some of the obvious faults which 
render radar particularly susceptible to jam- 
ming, and the AJ aspects of the particular 
system were considered in detail. Some of the 
equipments on which such consulting service 
was rendered are the AN/APG-3, AN/APG-16, 
AN/APS-19, AN/TPL-1, and Mark XII radar. 

Early in the design of the AN/APS-19, 
recommendations were requested for any de- 
sign changes which would improve the AJ 
characteristics of the final model. Several 
measures were proposed. These included the 
provision of a manual gain control to permit 
homing on jamming, removal of the i-f gate, 
addition of a short time-constant video cou- 
pling, and widening the video bandwidth. Also, 
the designers of the equipment were given 
information on methods used to determine the 
performance of the AJ features. No data are 
available to show the efficacy of the measures 
recommended. 

The U. S. Navy requested the AJ Practices 
Panel to recommend changes in the design of 
the Mark XII fire-control radar which would 
reduce its vulnerability to jamming. After a 
study of the radar, a number of possible 
improvements in its AJ performance were 
suggested to the Navy. Here again, no final 


vulnerability studies are available to evaluate 
the usefulness of the AJ^ features. 

The AN/TPL-1 radar (an S-band, antiair- 
craft fire-control equipment) was referred to 
the AJ Practices Panel for study while it was 
still in the prototype stage. In cooperation with 
the design engineers, a very close examination 
of the equipment was made and jamming tests 
were conducted on the prototype. As a result, 
a number of circuit changes were recommended 
from the AJ point of view. It was feasible to 
include most of the features suggested in the 
final design, and the production model was 
tested for jamming vulnerability (see Section 
13.4.1). Compared to previous equipments 
without built-in AJ features, the TPL-1 suffers 
much less loss of operating efficiency; in addi- 
tion, an AJ switch which throws in a short 
time-constant coupling circuit permits a defi- 
nite improvement in performance under jam- 
ming conditions. It was considered, therefore, 
that the efforts expended on the AJ circuits 
of the TPL-1 were amply justified and that 
the results exemplify the benefits of sound 
AJ engineering. 


13.3 FUNDAMENTAL AJ STUDIES 

The first step in an AJ research program, 
of course, must be to determine what it is that 
permits a radar to be jammed. As found from 
theoretical calculations, from basic laboratory 
experiments, and from vulnerability studies of 
particular systems, the effectiveness of a 
jamming signal depends both on the character- 
istics of the radar and on the nature of the 
jamming. This result leads quite logically to 
two further steps: the study of the effects of 
various jamming signals upon different radar 
types, and the study of basic methods for im- 
proving radar system operation in the presence 
of jamming. 

Such studies were made and are described 
in this section. In many cases, theoretical 
analyses were carried out in addition to the 
experimental investigations, either in advance 
or concurrently; these are discussed in detail 
in Chapter 6, and specific references to the 
proper sections thereof are given at the appro- 


252 


RADAR ANTIJAMMING STUDIES AND TRAINING 


priate points below. Not only did the theoretical 
work help give direction to the experiments 
and indicate their goals, but if it was con- 
firmed by the experiments it enabled their 
results to be generalized considerably. It should 
be noted that the results of these fundamental 
AJ investigations were useful not only in the 
protection of radars against jamming but also 
in the design of jamming transmitters and in 
the analysis of their capabilities. 

The AJ program in the United States did 
not completely follow the logical pattern of 
basic research succeeded by developmental 
research and then specific engineering. As 
various agencies became engaged in the AJ 
problem, progress was made in all three phases 
at once: more exact understanding of jamming 
effects, more detailed understanding of radar 
and AJ circuit characteristics, and more en- 
lightened engineering of application. The work 
was done somewhat in parallel among the 
various organizations, with informal individual 
liaison and joint-committee activities serving 
to maintain a nominal overall direction to the 
effort. Even within a particular organization, 
it was usual to find both basic research and 
specific engineering in progress simultaneously, 
often within the scope of a single project. 


13.3.1 Techniques and Circuits 

In the investigation of the AJ abilities of 
various radar systems and circuits, the prob- 
lems to be solved are the specific determination 
of the characteristics contributing to jamming 
susceptibility and the development of refine- 
ments and changes in circuit design which yield 
improved characteristics. A good understand- 
ing of these matters is essential to the final 
technical step of engineering suitable AJ 
characteristics into specific radars. 

Circuits and Methods 

The projects directed to such basic AJ 
research were quite varied and can best be 
described on a more or less chronological basis. 

High-Pass Filters. An early investigation of 
the design requirements for high-pass video 
filters was performed as an adjunct to a suscep- 


tibility study of the SCR-268. The possibilities 
of using such filters, suggested in a very early 
report,^®^ were experimentally examined, and 
it was concluded that a simple RLC filter was 
the most satisfactory. The filter was found 
quite effective in reducing the confusion on a 
deflection-modulated scope resulting from jam- 
ming modulated at a low frequency.'^^^’ 
Further consideration was given to the high- 
pass filter in connection with its use in the 
Navy Mark IV (FD) radar; it was found at 
this time that a simple RC filter (with the 
RC product equal to the radar pulse length) 
was practical and valuable in removing modu- 
lation components of the jamming resulting 
from the lobe switching. 

Back Bias. The matter of back bias also re- 
ceived considerable early attention, as a means 
for improving the overload limit level of a radar 
receiver. It was found that, on a steady-state 
basis, a back-biased i-f amplifier would with- 
stand a jamming signal equal to its normal gain 
times the signal level which caused overload 
without back bias. Further, in a multistage 
amplifier, each stage should be individually and 
successively back-biased as its input jamming 
signal level increased. Amplifier-type back- 
biasing circuits were found to be able to equal 
the performance of manual biasing and to 
follow a medium frequency-modulation en- 
velope as well. Cathode-degenerative biasing 
was found much less effective. 

Gain Control. In the course of the back-bias 
work, comparisons were made between one type 
of manual i-f gain control and the back-biasing 
methods. It was found that the ultimate bene- 
fits of a gain control in the reduction of over- 
load jamming effect were less than those of an 
optimum back-bias system. However, the avail- 
ability of a gain control on current radar 
receivers and its simplicity as compared with 
the biasing schemes made it sufficiently im- 
portant as an operational AJ measure to war- 
rant an extensive comparison of grid, cathode, 
screen-grid, and plate-screen-grid controls. 
Concurrently, operational radar jamming tests 
indicated the usefulness of informed gain- 
control manipulation. The study brought out 
the importance of controlling gain at an early 
i-f stage and of controlling a sufficient number 


FUNDAMENTAL AJ STUDIES 


253 


of stages to achieve the necessary overall range. 

Oscillator Detuning. A similar study was 
made to establish the limits of another opera- 
tional AJ feature: local oscillator detuning. In 
general, it was found that local oscillator 
detuning functioned in the manner of gain 
control to prevent overload, with the added 
advantage of discriminating more effectively 
against slightly off -tune jamming. 

Integration. By and large, the early AJ 
projects were concerned with remedies for the 
simpler types of jamming. Basic studies had 
early shown the difficulty of countering complex 
jamming such as pure or direct-noise amplifier 
(Dina) noise. A research program was insti- 
tuted on the possibilities of integrating (or 
averaging) a noise jamming pattern on an 
oscilloscope, either photographically or other- 
wise, in order to favor a steady repetitive pulse 
over the random noise. Tests coordinated with 
theoretical studies (see Section 6.2.2) indicated 
a practical limit of 6-db gain (over direct view- 
ing) through using time integration of a 
deflection-modulated scope by photography or 
long-persistent cathode-ray screen methods.'^^* 
379, 575, 583 ^^s felt that there were no practical 

applications for this method as an AJ measure 
in the existing war program. 

Errors from Lobe Switching. The practical 
problems of fire-control radar emphasized the 
importance of maintaining linearity in the 
receiving system of a lobe-switched radar to 
prevent directional errors from differential 
jamming overload between the lobes. Several 
ideas for reducing such errors were investi- 
gated, including methods to increase the 
dynamic range and linearity of the second 
detector. A comparison between square-law and 
diode detectors was made®®^ in connection with 
a specific engineering AJ application to the 
SCR-268. An experimental study was made of 
the idea of lobe switching only the transmis- 
sion of the radar, with reception on a single 
fixed receiving antenna; the results, as ex- 
pected, showed that errors caused by off -target 
jamming were eliminated.^^^ 

Anti-Window Devices. Methods for tracking 
targets through ground clutter, sea clutter, 
clouds, and Window received attention from 
practically all radar and radio countermeasures 


[RCM] laboratories in the United States. The 
possibilities of the high-piass video filter against 
clutter on air-to-surface vessel [ASV] radar 
were noted in field tests.®^^ An early field test of 
the detection of propeller modulation as a 
means of differentiating between aircraft and 
decoy echoes^^^ preceded an extensive research 
program on the Sambo project at Radiation 
Laboratory and Naval Research Laboratory; 
this was followed at a later date by a project 
in which the usefulness against clutter of an 
aural detector for propeller modulation and 
doppler beats was demonstrated.®^^ Another 
approach to the anticlutter problem was the 
extension of the dynamic range for signals 
presentable on an intensity-modulated indi- 
cator. Several “gain-compressing” video cir- 
cuits were devised, the most promising one 
using crystals as nonlinear circuit elements.'^®” 
Consideration was given to the use of a very 
short time-constant coupling in the video as 
a differentiator; a theoretical analysis (see Sec- 
tion 6.3.1) showed that if this device were 
combined with an increased receiver bandwidth 
it would be equivalent to shortening the radar 
pulse length. 

The differentiation of real naval targets from 
decoys or spoofs was solved with a radar modi- 
fication which made it practical to observe the 
multireflection detail of a ship as compared 
with the simple, single-surface reflection of a 
spoof. It was found that observation of the 
behavior of an echo as a slight frequency modu- 
lation was applied to the radar transmitter 
signal, or simply study of the echo with a high- 
definition receiving system and expanded-sweep 
scope, permitted a reliable interpretation of a 
given echo®®® (see Section 6.3.1). 

Miscellaneous Devices. Several devices and 
circuits proposed or used by other AJ groups 
were examined in the course of the Division 
15 program, including a study of a pulse- 
amplitude discriminating system (George Box) 
and an operational check of the German look- 
through device known as Stendal B or 
Goldammer, which operated by selecting the 
proper polarization. Reports were not issued 
on this work. 

In addition, several original ideas for AJ 
measures were studied at RRL. The use of 


254 


RADAR ANTIJAMMING STUDIES AND TRAINING 


lobing for transmission only was noted above. 
A method for the cancellation of separately 
induced cross-polarized components of a circu- 
larly polarized jamming signal was shown to 
be practical in both laboratory and field tests. 
This work aroused Service interest from the 
offensive as well as defensive RCM point of 
view, because of the widespread Allied use of 
circularly polarized jamming."^^^ As a further 
outgrowth of this project, a jamming cancella- 
tion system was applied as a look-through aid 
to a setting-on receiver in a spot-jamming 
system and successfully flight-tested.®^^ The 
idea was incorporated in the last jammer 
system development. Elephant (see Chapter 
11 ). 

Summary and Conclusions 

The foregoing would indicate that the basic 
research program of Division 15 in the AJ 
field was somewhat disconnected. To a certain 
extent, this activity was fitted into a more 
complete overall pattern, involving all labora- 
tories engaging in AJ work; in retrospect, 
however, it is apparent that this overall effort 
might have been more closely coordinated. On 
the other hand, the study, research, and field 
tests performed by United States agencies 
led eventually to a reasonably definite body of 
AJ philosophy based on fact which can be 
summarized as follows : 

1. High-power high-definition radar systems 
have been proved in practice to be superior in 
AJ operations. 

2. Tunable radars which have been developed 
for both low frequencies and microwaves in the 
form of experimental models have proved the 
value of a single-dial tunable radar as an AJ 
system. There is factual evidence that tuna- 
bility is foremost as an AJ measure. Frequency 
spread of radars, which serves the same func- 
tion, is a corollary and equally important. 

3. Practical incorporation of dynamic ranges 
in receivers sufficient to handle inputs of 
hundreds of millivolts has been demonstrated, 
with methods running from clean high-power 
i-f amplifier design to clever trick-feedback 
circuits and automatic biasing arrangements. 
Many practical circuits have been evolved espe- 
cially to handle strong clutter signals. 


4. The useful limits of video filtering and the 
proper design features of video filters have 
been shown both for antijamming and for anti- 
clutter work. 

5. The advantages of clean design and of 
circuit stability as aids to AJ performance have 
been demonstrated. 

6. The requirements for signal presentation 
have been well established, including the AJ 
advantages of deflection modulation and sharp 
focus, and, in a few cases, of persistent 
phosphors. 

7. The relation of video and i-f bandwidths 
to each other and to the radar signal spectrum 
have been established. The optimum i-f band- 
width is equal to 1.3/pulse time duration, and 
the video must be equal to or greater than the 
total i-f width. 

8. The importance of linearity in fire-direc- 
tion radar receiver circuits has been shown and 
an indication found of how it may be achieved. 

9. The value and necessity of moving-target 
indication schemes have been proved, but 
demonstration of the extreme vulnerability to 
electronic jamming inherent in such systems 
has led to the problem of combining tunability 
with moving-target detection. 

10. Pulse width and amplitude selecting 
schemes have been shown to have value in 
limited circumstances, especially where they 
serve to alleviate operator fatigue. 

Special AJ measures and circuit tricks, be- 
cause of their limited scope, are not recom- 
mended for general radar application. Radar 
design should be strengthened along lines of 
tunability, stability, good shielding, wide 
dynamic range, linearity, higher power, opti- 
mum definition, ease of operation and interpre- 
tation, and freedom from clutter interference. 
^‘Doctoring’" for special cases of jamming 
should be incorporated only when such a special 
case exists, to eliminate much normally useless 
circuitry. However, the limits and capabilities 
of representative special AJ circuits must be 
known in case their emergency use is required. 
The manufacturer should provide basic AJ 
design, and the Armed Services should have 
trained specialists on hand to doctor, point out 
operating tricks, and educate the operators in 
AJ continually. 


FUNDAMENTAL AJ STUDIES 


255 


13.3.2 Studies of Jamming Signal 

Effectiveness 

During 1943 and the early part of 1944, a 
series of laboratory studies^^^’ 
were carried out under carefully controlled 
conditions to determine the relative effective- 
ness of various types of jamming signals 
against both deflection-modulated and inten- 
sity-modulated indicators. The primary pur- 
pose of these studies was to determine the most 
efficient type or types of jamming for use in 
offensive countermeasures ; in the course of the 
work, however, information of interest from 
the AJ point of view was also obtained. The 
results are summarized here, first from the 
point of view of offensive countermeasures and 
then from the AJ point of view. Theoretical 
analyses of some phases of the work are dis- 
cussed in Section 6.2, and the results of simi- 
lar studies on communications systems are 
described in Chapter 9 and also in Section 
8 . 2 . 2 . 

The efficiency of the various types of jam- 
ming signals was measured in terms of the 
jam-to-signal [J/S] ratio — the ratio of the 
jamming power to the signal power — in such 
a way that the radar pip is detectable just 50 
per cent of the time. In the studies of both 
amplitude- and frequency-modulated jamming, 
J /S is the ratio of the rms unmodulated carrier 
power of the jamming to the rms of the radar 
output multiplied by the inverse of the duty 
cycle (the so-called '‘peak power” of the pulse) . 
In the case of pure Dina noise, J/S is the ratio 
of the rms of the noise to the "peak power” of 
the pulse. For pulse jamming, two types of 
ratios were used. The ratio of the peak power 
of the jammer pulse to the peak power of the 
radar pulse is J(peak)/i8. The ratio of the 
rms of the jammer output to the peak power 
of the radar pulse is J(rms)/S. 

All of the types of jamming studied may be 
classified as either periodic or random. Periodic 
jamming includes sine-wave amplitude modula- 
tion, sine wave frequency modulation, and 
periodic pulse jamming; and random jamming 
includes noise amplitude modulation, noise fre- 
quency modulation, Dina, noise (no carrier), 
and random-pulse jamming. 


Results from the Offensive RCM Aspect 

All types of periodic jamming are completely 
ineffective in the absence of overloading, 
against any system which employs a deflection- 
modulated scope. 

All types of random jamming are effective 
against deflection-modulated scopes. The degree 
of effectiveness, however, varies among the sev- 
eral types and also in a function of the several 
parameters of each particular type. 

With noise amplitude modulation, an in- 
crease in percentage of modulation increases 
the effectiveness of the jamming by an amount 
equal to the resulting additional power in the 
sidebands. The variation in the effectiveness of 
the jamming as a function of the degree of 
clipping of the modulating noise is dependent 
on the bandwidth of such noise. If the band- 
width of the noise is not greater than that of 
the receiver, varying the peak factor from 
5 to 1.5 does not greatly change the effective- 
ness of the jamming. If, however, the band- 
width of the noise is of the order of ten times 
the bandwidth of the receiver, then greater 
clipping results in an increase in effectiveness 
equal to the resulting increase in the power of 
the sidebands. 

The importance of the dependence of the 
effect of clipping upon the bandwidth of the 
noise should be emphasized. For example, with 
a noise a-m jammer which has a bandwidth 
of the order of ten times the receiver band- 
width and which employs highly clipped noise 
for modulation, one can not only jam the 
channel to which the jammer is tuned more 
effectively than with a jammer of equal total 
sideband power which has a bandwidth equal 
to that of the channel, but one can also jam 
almost as effectively almost all the other 
channels covered by the wide-band jammer. 
The fact that ten times as much energy is ac- 
cepted by the receiver when the narrow-band 
jammer is employed is offset by the fact that 
the narrow-band clipped noise appears clipped 
on the scope of the receiver and hence is a much 
less efficient jamming signal. 

With noise frequency modulation an increase 
in clipping, as a general rule, results in more 
effective jamming. In addition, the larger the 
frequency deviation, the greater is the jamming 


256 


RADAR ANTIJAMMING STUDIES AND TRAINING 


effectiveness (within the limits studied). If the 
bandwidth of the noise used for frequency- 
modulation is too narrow or too wide, the jam- 
ming is less uniform than if the optimum band- 
width is used. The optimum bandwidth de- 
pends upon the frequency deviation, the noise 
peak factor, the bandwidth of the modulating 
noise, and the receiver bandwidth. 

Sine-wave frequency modulation plus noise 
amplitude modulation is an effective jamming 
signal. The best case of such jamming is about 
as effective over the barrage width as the best 
case of jamming by noise frequency modulation. 
Adding sine-wave frequency modulation with a 
frequency deviation of the order of the receiver 
bandwidth to narrow-band noise amplitude 
modulation makes the noise appear random on 
the scope of the receiver and increases the 
effectiveness of the jamming by about 7 db. 
Sine-wave frequency modulation plus noise 
frequency modulation is inferior as jamming 
both to sine-wave frequency modulation plus 
noise amplitude modulation and to noise fre- 
quency modulation. 

If noise frequency modulation plus noise am- 
plitude modulation is produced by one noise 
source, the energy spectra tend to be markedly 
asymmetrical and the effectiveness of the jam- 
ming varies greatly over the barrage width. 
Systematic relations exist between the f-m and 
a-m sidebands such that in some cases they 
tend to reinforce and some cases cancel each 
other. If independent noise sources are em- 
ployed, symmetrical energy spectra are ob- 
tained. The best case of noise frequency 
modulation plus noise amplitude modulation, 
however, is no better than the best case of noise 
f-m jamming. 

The higher the upper frequency limit of the 
noise used to trigger random-pulse jamming, 
the more such jamming looks like receiver noise 
and the more effective it is. In designing a 
random-pulse jammer, it makes little difference 
whether the primary consideration is peak 
power output or rms power output. In either 
case, the upper frequency limit of the trigger- 
ing noise should be about five times the band- 
width of the receiver to be jammed and the 
pulse length should be of the order of 1/15 X 
receiver bandwidth. Under such conditions, the 


barrage width is about equal to 1/1.4 X pulse 
length. 

Results from the AJ Point of View 

Periodic jamming, although completely in- 
effective against a deflection-modulated scope 
in early-warning [EW] radar systems, is, gen- 
erally speaking, effective against all systems 
which employ an intensity-modulated scope. 
Moreover, many types of random jamming are 
much more effective against an intensity- than 
against a deflection-modulated scope. These 
two facts make it appear highly desirable that 
auxiliary A scopes be provided for radar sys- 
tems which normally employ intensity-modu- 
lated scopes and which are likely to encounter 
jamming of any kind. 

The relation between the effectiveness of any 
given type of jamming and overloading of the 
receiver depends upon the characteristics of 
the particular receiver being jammed. Although 
the increase in some cases is negligible, both i-f 
and video overloading tend, in general, to in- 
crease the effectiveness of all types of jamming. 
It is important, therefore, that radar receivers 
be designed in such a manner that the possi- 
bility of overloading is minimized. 

An analysis of the results obtained indicates 
that in many cases a variable receiver band- 
width would be a useful AJ measure. Thus, for 
example, as indicated above, increasing the 
frequency deviation increases the effectiveness 
of noise frequency modulation in jamming. 
The converse of this is that, if the frequency 
deviation of the jamming is held constant, then 
increasing the receiver bandwidth will decrease 
the effectiveness of the jamming. Similarly, if 
one is working through random-pulse jamming, 
doubling the receiver bandwidth may cause a 
marked decrease in the effectiveness of the 
jamming. Under certain circumstances with 
noise amplitude modulation and with Dina 
noise, a decrease in the receiver bandwidth re- 
sults in a decrease in the effectiveness of the 
jamming. 

13-^ STUDIES OF SPECIFIC EQUIPMENTS 

After the fundamental principles of AJ had 
been investigated, the next step was to apply 


STUDIES OF SPECIFIC EQUIPMENTS 


257 


them. The methods used to ensure the incor- 
poration of these principles in new radars has 
been discussed, but there remained the problem 
of the radars already in use which had been 
designed without regard for AJ considerations. 
This problem was attacked by studying the 
vulnerability of such equipments to jamming 
and then designing modifications, if possible, to 
render them less vulnerable. 


^ ^ Jamming Susceptibility of 
U. S. Radars 

In order to improve the performance of a 
radar set in the presence of enemy jamming, 
it is necessary to know quantitatively how much 
its operation is impaired by Window and by 
the various types of electronic jamming signals 
which may be encountered. The problem of 
Window jamming susceptibility is considered 
in Chapter 12. The paragraphs below describe 
the numerous investigations on the suscepti- 
bility of radar sets to electronic jamming, as 
well as the one study that was made of the 
susceptibility of the long-range radio-naviga- 
tion (Loran) system. In these studies, after the 
vulnerability of an equipment had been deter- 
mined, a circuit analysis was generally carried 
out (in a varying degree of detail) to determine 
the reasons for the observed effects of the jam- 
ming, so that remedial measures could be 
recommended. 

Results of Studies 

In accepting susceptibility projects from the 
Armed Services, the policy was to make at least 
one prototype study of each type of radar equip- 
ment but not to undertake numerous studies 
of a given type. The various sets for which 
studies have been made are listed in Table 1, 
together with pertinent data and references. 
The arrangement is roughly chronological. The 
results of these studies are discussed in the 
paragraphs below. The AJ modifications listed 
are described in detail in the next section. 

In general, it may be said that the United 
States radar equipments tested were rather sus- 
ceptible to electronic jamming. This was par- 
ticularly true of searchlight-control [SLC] and 


fire-control sets, such as SCR-268, Mark IV, and 
AN/APG-1, where high directional accuracy 
must be maintained if the set is to remain func- 
tional. SCR-545 and AN/TP L-1 showed better 
performance, particularly the latter, a new set 
with much better AJ design. 

The ASV sets studied were affected by jam- 
ming to the point where a ship target could 
screen its range over all azimuths by means of 
a medium-power jamming transmitter. This 
was true even in the case of a recent set such 
as AN/APS-4. 

The work on the radar homing bomb [RHB] 
and Mark XXXI sets deserves special mention. 
These are radar- controlled bombs that auto- 
matically home on a target, and they proved to 
be extremely susceptible to electronic jamming. 
Automatic tracking radars are inherently eas- 
ier to jam than manually controlled sets, but the 
analysis of these sets led to several suggestions 
for improvement. The same was true of the 
AN/APG-1. The performance of the automatic 
tracking in SCR-545 was found to be much 
better. These studies led to detailed considera- 
tion by radar design groups of the autotrack 
problem. 

Measurement Techniques 

The results of the laboratory susceptibility 
studies were expressed in terms of J/S ratio 
(ratio of jamming power to peak-signal power). 
A direct calibration of these ratios was obtained 
by observing the beat resulting from simultane- 
ous reception of pulse and continuous-wave 
[c-w] jamming. An absolute scale of jamming 
power was established by measurement of the 
field strength at the radar antenna, or, in the 
case of S-band studies, by use of a calibrated 
thermistor bridge. 

For S-band studies, the Boonton Type L-102 
variable-phase pulse generator was found to be 
very useful. A laboratory modification was 
worked out whereby these generators could be 
converted to c-w or modulated c-w operation 
and used as sources of test jamming signals. 
Both normal and converted L-102 units are 
equipped with calibrated output attenuators and 
built-in thermistor bridges. 

In addition to laboratory susceptibility stud- 
ies, tests were carried out on the jamming sus- 


258 


RADAR ANTIJAMMING STUDIES AND TRAINING 


ceptibility of several sets during actual field 
operations. Although this work was intended 
primarily as a check on the laboratory suscepti- 
bility studies, some of it was pioneer work in 
the field operation of jamming transmitters for 
spot jamming.®24 

For field susceptibility tests on S band, it 
was necessary to develop a jamming trans- 
mitter.^^^ The result was a quickly built equip- 
ment rugged enough for field service, using a 
Type 410-R klystron. It was used on Lake Okee- 


Navy Bureau of Aeronautics, which proceeded 
with the actual field work. 

Measurements of jamming susceptibility had 
a double function in the AJ program. In the 
first place, when combined with an estimate of 
the enemy's ability to produce jamming signals, 
they made possible an evaluation of the general 
defensive position of United States systems. It 
was on the basis of this evaluation that the 
military supported corrective measures either 
to meet an immediate need or as insurance. In 


Table 1. Radar susceptibility studies and AJ modifications. 


Set No. 

Type 

Frequency 

References* 

AJ modifications 

Modificationf 

references 

Loran 

Navigational 

1.95 me 

516 



SCR-268 

Land-based SLC 

200 me 

520 

E-1610, E-1601, E-1602, 
E-1602A, E-1606, E-1607 

794, 620, 681 

SCR-521A 

ASV search 

176 me 

532 



Mark IV 

Ship-borne fire- 
control 

700 me 

549 

E-510, E-515, E-2106 

401, 406, 438, 469, 
517 

ASG 

ASV Search 

S band 

537, 538, 
597 



SCR-717B 

ASV Search and 
LAB 

S band 

570 

L-901 

542, 380 

RHB 

Guided missile 

S band 

633 



Mark XXXI 

Guided missile 

S band 

648 



SCR-720A 

AI and ASV 

S band 

684 



ASB 

ASV search 

5.15 me 

680 

E-410, E-412, E-413, E-409, E-411 

680, 795 

AN/APQ.5B 

LAB attachment 

Video 

703 

Field modification 


AN/APG-1 

Airborne auto- 
matic GL 

S band 

712 

Field modification 


AN/APS-4 

ASV and LAB 

Xband 

713 



AN/APA-16 

LAB attachment 

Video 

713 



AN/TPL-1 

Land-based SLC 

S band 

717 



SCR-545 

Duplex search 
and GL 

200 me 

S band 

729 




* Reports concerned with the susceptibility studies, 
t Reports concerned with AJ modifications (see Section 13.4.2). 


chobee, Florida, against the ASG and SCR-717B 
radars.^®^ This transmitter was the forerunner 
of later S-band jamming transmitters, and the 
tests in which it was used served to demon- 
strate the practicality of spot jamming of S- 
band ASV radar systems. 

A similar situation developed in 1945 when 
field susceptibility tests on the AN/APS-4 X- 
band ASV radar were contemplated. A field 
jammer for use in the tests was developed using 
experimental models of the RCA Type A-131 
magnetron.’’’^^ Because of the ending of World 
War II, the equipment was transferred to the 


the second place, the detailed analyses of cir- 
cuits and operation that formed a part of most 
susceptibility studies were the technical basis 
for AJ modifications and for advice on new 
radar design and development. 


13.4.2 Modifications for Existing 

Equipments 

Soon after AJ research was begun, it was 
felt that an immediate need existed for giving 
AJ attention to several specific radars then 


STUDIES OF SPECIFIC EQUIPMENT 


259 


widely used by the Armed Services. The first 
radar studied was the Navy Mark IV (FD), for 
which the application of several known AJ 
palliatives was considered. From a previous sus- 
ceptibility study and from a field jamming trial 
several possibilities were indicated, and ex- 
perimental work was undertaken. 

At various later dates, similar applications of 
AJ engineering were attempted for the SCR- 
268, SCR-717, and ASB radars. In all these 
cases the intention was to ''clean up” any par- 
ticularly bad features of receiver circuit design, 
and often to add simple attachments, such as 
switchable high-pass filters or detuning con- 
trols. It is difficult to set any value on this pro- 
gram, for there were no cases reported where 
any of these devices saw operation against jam- 
ming. Many of the units did reach the Armed 
Services, however, and for their insurance value 
and the experience gained in their development, 
the effort can be considered generally construc- 
tive. Table 1, in the preceding section, lists the 
more important devices completed, and they are 
described in the summary below. 

Navy Mark IV (FD) Radar 

A number of AJ devices were designed for 
this fire-control radar. These included the fol- 
lowing. 

Plug-in High-Pass Filter E-510. A simple 
RC video filter which could be switched in as 
needed, with an RC product approximately 
equal to the pulse length, was arranged for in- 
stallation by placing an adapter plug under a 
video amplifier tube.^^® This device was procured 
as a field modification kit by the Navy. 

Local Oscillator Detuning Attachment E-512, 
This modification, consisting of a small variable 
condenser to provide vernier tuning of the local 
oscillator, was not procured, but it was de- 
scribed in order to have the design information 
available should need arise.^^^ 

Very High-Pass Video Filter E-515. This 
device involved several additional tubes and in 
effect replaced the normal second detector and 
part of the video chain. It provided the AJ ad- 
vantages of a more linear detector and of a 
choice of three very high-pass, sharp cutoff 
filters. It was based on the fact that a jamming 
carrier is usually sufficiently off tune to produce 


a medium- or high-frequency beat with the 
pulse signal. The filters C(^uld be chosen to select 
and amplify this beat signal, presenting it di- 
rectly on the sqope screen. Navy procurement 
put this attachment on most of the Navy Mark 
IV radars, and later the unit was adapted to 
the Army SCR-296 radar.^^® 

Army SCR-717B Radar 

A laboratory susceptibility study''"^^ and a 
series of flight tests^^®. 542 design of 

the L-901 replacement video unit. This device 
mechanically and electrically replaced the usual 
SCR-717B video to provide improved video 
bandwidth, increased dynamic range, and a 
switchable high-pass filter. Limited procure- 
ment resulted in the installation of a few units 
in operational radars. Although the nature of 
the modification was such as to improve the AJ 
characteristics of the radar, the greatest oper- 
ational interest was in its action against sea 
clutter. 

Army SCR-268 Radar 

The SCR-268 received early attention in the 
first radar vulnerability study^^o 
vehicle for early high-pass filter studies. Early 
in 1944, a somewhat more extensive program of 
specific AJ modifications was undertaken. 

Plug-in High-Pass Filter E-1610. The first 
project resulted in the mechanical adaptation 
of a plug-in high-pass video filter using a single 
switchable RC section. This unit was produced 
in limited quantity for shipment to the stricken 
SCR-268’s at Anzio in the Mediterranean Thea- 
ter of Operations. However, it arrived slightly 
later than a superior AJ device, a 3,000-mc re- 
placement radar for the 268’s.'^®^ 

Replacement Detector and Video Units 
E-1601/1602. These two devices were designed 
to work together with certain circuit changes 
to provide the following advantages: increased 
video dynamic range, increased video-frequency 
bandwidth, increased linearity (detector and 
video), availability of switchable high-pass fil- 
ters, and increased gain-control range. The two 
units were arranged to replace the detector and 
video stages. The E-1601 came in the form of 
fabricated adapter plugs which were inserted 
in the second detector and first video sockets 


260 


RADAR ANTIJAMMING STUDIES AND TRAINING 


in the 268 receiver unit, while the E-1602 was 
a fabricated box which mounted over the 
sockets normally occupied by the final video 
stage and was connected into the circuit by 
means of a plug adapter. The gain-control range 
extension was achieved by applying the control 
to an additional i-f stage.^^^’ 

Limited procurement enabled some of the 
modification kits to be shipped to the few re- 
maining operational SCR-268 radars. Improved 
models of the video unit (E-1602A) used a 
simplified circuit; E-1606 provided low-pass 
filters as well as high-pass. These units were not 
procured. 

Navy ASB Radar 

An attempt was made to dovetail specific 
“gadget” engineering with laboratory suscepti- 
bility and field test studies. A series of jamming 
flight tests was followed by a laboratory sus- 
ceptibility study, which led to the preliminary 
design of several AJ modification devices. A 
second flight test program served to indicate the 
operational feasibility of these modifications. 

Plug-in High-Pass Filter E-JflO. Similar to 
those for the 268 and Mark IV radars, this filter 
provided for remote control by the radar opera- 
tor and also a rearrangement of the circuit 
connections to apply one section of the detector 
duodiode as a fast-recovery diode on the RC 
filter. A limited number of these units were pro- 
cured and distributed by RRL. 

Transmitter Remote-Tuning Attachments 
E-^09 and E-^13. A simple mechanical drive 
unit was arranged to provide the radar operator 
a chance to tune the transmitter as well as the 
receiver, making a completely tunable radar. 
Actual flights against a carefully monitored 
spot jammer revealed that the radar operator 
using a tunable system had a definite advantage 
over the jammer and could usually make what 
would have been successful torpedo-approach 
runs. 

Gang Tuning Attachment E-^11. This was 
a gear-box unit which enabled ganged drive of 
the normal receiver tuning and the added trans- 
mitter tuning units. The unit simplified system 
detuning and, through a disengaging gear ar- 
rangement, allowed separate receiver tuning. 
With the E-409 and E-413 units, the device was 


developed to the prototype stage and turned 
over to the Navy Bureau of Aeronautics for 
consideration. Rapid replacement of the ASB 
radars reduced the potential value of these 
units.^*^’ 

The actual contribution of the gadget-design- 
ing program to the AJ effort was not important. 
To a limited extent, however, the program 
served to indicate the possibilities and limita- 
tions of field modifications should real AJ needs 
arise, and above all to emphasize the importance 
of tackling the basic AJ problems from the 
point of view of radar design. 


^3- AJ TRAINING ACTIVITIES 

The importance of operator training as an 
AJ measure was brought out forcefully by ex- 
periences in making susceptibility studies and 
in operating a variety of radar systems in the 
field. A great deal can be done to reduce or 
nullify the effectiveness of jamming by proper 
manipulation of receiver and oscilloscope con- 
trols. For instance, in the case of a search set 
that overloads easily, proper adjustment of the 
manual gain control can improve the perform- 
ance a thousandfold or more. Careful training 
of operators in the use of these controls is abso- 
lutely necessary, if the improved performance 
is to be realized. Operator training also results 
in a greatly increased ability to read through 
jamming patterns which confuse but do not 
completely obliterate the target indications on 
the cathode-ray oscilloscope. Another purpose 
of training is to ensure that operators continue 
to operate their radar when jammed, rather 
than shut down on the supposition that the set 
is defective. In this way much useful informa- 
tion may be obtained that might otherwise be 
lost because of panic. 

The AJ training activities in Division 15 may 
be divided into four parts: lectures on AJ to 
groups of Army and Navy officers coming to 
RRL for RCM training, a complete AJ training 
course for Navy officer-instructors, develop- 
ment of transmitters and signal generators for 
use in AJ training, and activities in connection 
with training films. 


AJ TRAINING ACTIVITIES 


261 


13.5.1 Officer Training Courses 

During the first 2 years or so of RCM activity, 
the United States RCM program was in the 
development stage. Toward the end of this 
period some equipment was in production and 
small quantities were available to the Armed 
Services. Training of personnel in the use of 
this equipment became an important problem. 
Since RRL was the seat of a great deal of the 
development, it was appropriate that it should 
assume the responsibility of training selected 
groups of officers. The training took the form 
of a series of lectures on the various phases of 


practice at the Naval Training School, Fort 
Lauderdale, Florida. Two officers from this first 
group then took over the job of training suc- 
ceeding groups ,of officer-instructors. A sizable 
syllabus of reference and study material was 
prepared at RRL and distributed to the officers 
attending the RRL part of the course. This 
syllabus contained a laboratory manual for the 
four laboratory experiments,^^® a condensed 
summary of information on AJ techniques and 
devices, and numerous reprints of pertinent 
technical articles and reports.^®® For the oper- 
ational part of the instruction at Fort Lauder- 
dale, considerable RCM equipment was installed 


Table 2. AJ training equipment. 
RRL Power 


No. 

Type 

Project No. 

Frequency 

output 

References 

Remarks 

AN/UPT-1 

Practice jammer 

F-2800 

450-720 me 

8-4 w 

802, 803, 
456 

Modified AN/APT-2. 


Practice jammer 

F-2000 

450-720 me 

8-4 w 

456 

Modulations differ 
from those of 
AN/UPT-1. 

AN/UPT-T4 

Practice jammer 

F-3800 

175-550 me 

7-30 w 

456, 798, 

Modified AN/APQ-2. 

RF-9/UPT 

Oscillator 

F-4100 

100 kc, 400 kc 
2-power fre- 
quency 

Low 

456, 797 
799 

Modulator for 
AN/APT-2, 
AN/APT-3, or 
AN/APQ-2. 


Jamming signal 
generator 

A-1700 

2,400-3,700 me 

6 mw 

347, 796 

6-ft relay rack. 

TPQ-T2 

AJ training set 

P-525A 

90-270 me 

V 2 w 

800, 801 

Wide selection of 
modulations. 

TS-109/SPA 

AJ training at- 
tachment 

E-1300 


Low 

480 

For Navy Mark I, 
FD trainer. 


Switching unit 

E-2000 



476 

For use with SC 
radar. 


Jamming signal 
generator 

U-700 

450-1,000 me 

0.1 w 

804, 805 

Several modulations 
available. 


RCM equipment and techniques, repeated at 
suitable intervals. Lectures on AJ were included 
in these series and covered both AJ equipment 
and operational methods. Seven Navy courses 
and nine Army courses lasting one to two weeks 
each were given, with an average attendance of 
about thirty. 

The AJ training course for Navy officers was 
initiated at the request of the Bureau of Per- 
sonnel as part of an overall plan for providing 
AJ training in the various schools operated by 
that bureau. Twelve officers representing the 
schools attended a one-week course of lectures 
and laboratory work at RRL in Cambridge and 
a two-week course of lectures and operational 


on an 82-ft Coast Guard patrol boat and oper- 
ated against shore-based radar systems. This 
installation continued to be used by the Fort 
Lauderdale and Hollywood Beach training 
schools after the instructor training program 
was completed. 

13.5.2 Equipment and Films for AJ 
Training 

Table 2 summarizes the equipment developed 
for AJ training purposes. Several field jamming 
transmitters were modified for training, special 
signal generators were developed, and an AJ 
trainer attachment was engineered. 


262 


RADAR ANTIJAMMING STUDIES AND TRAINING 


The practice jammers (AN/UPT-1, AN/UPT- 
T4, and F-2000) were modifications of regular 
field jammers and were intended for field use 
where a sizable power output is necessary. A 
selection of modulations is available. The RF- 
9/UPT attachment plugs directly into a tube 
socket of standard jammers and provides modu- 
lations needed for AJ practice. The AJ training 
attachment TS-109/SPA was developed to meet 
a need for such a device expressed by the Navy. 
It is a generator to provide video-frequency 
jamming signals to the Mark I trainer, which 
is used to train operators for the Navy Mark III 
and IV fire-control radar systems. The device 


graphic techniques, and the furnishing of radar 
systems and jamming equipment. Films on 
which RRL acted in a consulting capacity are 
listed in Table 3. 


^ CONCLUSIONS AND RECOM- 
MENDATIONS 

The very limited extent of the enemy jam- 
ming and deception of our radar during World 
War II made a large-scale AJ effort unneces- 
sary. Sufficient basic work was done, however, to 
be able to meet AJ emergencies had they arisen. 


Table 3. AJ consulting on Army and Navy training films. 


Equipment 

Film No. 

Film title 

Service 

Classification 

ASG 

MN2867-E 

Radex PPI and B-Scan 

Navy 

Confidential 

ASB 

MN2867-B 

Radex ASB 

Navy 

Confidential 

Mark IV 

MN2867-C 

Pt 1 — Radex Fire-Control Radar Equipment 

Navy 

Confidential 

Mark IV 

MN2867-D 

Pt 2 — Radex Fire-Control Radar Equipment 

Navy 

Confidential 


MN2867-A 

Window 

Navy 

Confidential 

SCR-268 

TF-4-1320 

The Radar Set SCR-268, Pt 7 — Indicator Jamming 

Army 

Confidential 


TF-11-1420 

Pt 1 — Radar AJ for the Radar Operator — Receiver 
Adjustments 

Army 

Restricted 


TF-11-1421 

Pt 2 — Radar AJ for the Radar Operator — Recognition 
of Electronic Jamming 

Army 

Restricted 


TF-11-1422 

Pt 3 — Radar AJ for the Radar Operator — Window 

Army 

Restricted 

AN/TPL-1 

TF-44-1456 

Pt 1 — The Radar Set — Operation 

Army 

Confidential 

AN/TPL-1 

TF-44-1457 

Pt 2 — The Radar Set — Jamming 

Army 

Restricted 


will simulate both on- and off -target jamming 
signals with a wide selection of modulations. 
The TPQ-T2 signal generator was developed at 
General Radio Company, and the other equip- 
ments at RRL. 

The activities in connection with training 
films consisted partly in the production of proto- 
type training films on AJ and partly in the fur- 
nishing of technical consulting services to the 
Army and Navy on such films. Three prototype 
films were made (J-2, J-3, J-4), illustrating AJ 
techniques on the Mark IV (FD) and SCR-521 
radars and explaining the use of the E-510 
filter. In making these films, considerable work 
was done in developing techniques for cinema- 
tography of radar indicator screens. A consid- 
erable amount of assistance was requested by 
both the Army and Navy in connection with the 
AJ portions of radar operator training films. 
The type of consulting varied from film to film 
but included script editing, advice on photo- 


This research pointed up an overall lesson to 
guide the future of AJ activity and the develop- 
ment of electronic equipment in general. 

Perhaps the most important factor is that 
sound design is the best AJ feature that an 
equipment can possess. Furthermore, the best 
place to include such features is in the original 
design of the equipment. Although it is true 
that certain of the specialized AJ devices may 
prove to be useful and necessary under jam- 
ming conditions, they will be much more effec- 
tive if they are incorporated into the design 
than if they are retroactive modifications. Prog- 
ress has been made in securing the inclusion of 
sound AJ design in recently developed radar 
equipments, and it is hoped that this condition 
will prevail further in the future. 

Of very nearly equal importance as an AJ 
measure is a well-trained operator for the radar 
equipment. (This is true also in nonradar fields 
— see Chapter 9.) This conclusion was borne out 


CONCLUSIONS AND RECOMMENDATIONS 


263 


very forcibly by the radar system vulnerability 
studies, which showed that an operator who 
knew how to manipulate the radar controls in 
the presence of jamming was able to maintain 
much higher effectiveness of operation. The 
fundamental principles of the best operation of 
radar in the presence of jamming have been 
well developed in the laboratories, but the edu- 
cation of operators in the field is a continuing 
problem. Pamphlets, films, and actual practice in 
operating under jammed conditions were used 
as training measures by the Armed Services, 
and all are important. It must be emphasized, 
however, that there is no substitute for actual 
practice and that the use of training jammers 
against operational radar is a vital part of an 
adequate AJ training program. 

Of the total radar development effort in the 
United States during World War II, only a very 
small portion was devoted to AJ “doctoring’’ of 
existing radar. By far the greater part of the 
development concerned the application of sound 
engineering principles to new radar designs and 
to the best design feature of all the develop- 
ment of techniques to employ ever-expanding 
frequencies in radars. This is evidenced by the 
multitudes of new frequencies in use. 

Contrast this with the information obtained 


about the German scientific effort.®®^ No re- 
search at all on radar A^as done from 1941 to 
1943! When radar research was resumed, the 
effort was concentrated very heavily (up to 90 
per cent!) on trying to salvage the Wurzburg 
gun-laying equipment in the face of the jam- 
ming attack that had already begun. Even 
though they had captured some British S-band 
equipment by 1943, no German microwave 
radar appeared in operation until early 1945, 
and then in negligible quantities. In conse- 
quence, the Allied jamming effort was able to 
keep ahead of the Wurzburg improvements, a 
position which would have been very difficult to 
maintain had the German effort been concen- 
trated on diversified development. 

But it should not be assumed that the mere 
extension of radar designs to higher and higher 
frequencies constitutes complete freedom from 
jamming vulnerability. The United States 
X-band designs were believed safe solely on the 
basis of their frequency, but an X-band jammer 
of high potentiality was also developed. Ad- 
vances in basic h-f techniques and the applica- 
tion of them to operational equipment must be 
continued and the emphasis increased on carry- 
ing into new equipment designs the AJ lessons 
learned from World War II. 


Chapter 14 

RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


INTRODUCTION 

T he largest use of radio and radar counter- 
measures equipment during World War II 
was in the European and Mediterranean Thea- 
ters of Operations. The reasons for this are 
manifold. The Germans were much better 
equipped for a technical war than the Italians 
and the Japanese. Furthermore, they made very 
good use of the equipment that they had avail- 
able. 

Although radar had been developed inde- 
pendently by England, Germany, and the United 
States, Allied countermeasures were really 
started in England, where the necessity of 
counteracting the German bombing attacks by 
any means available made the use of radio 
countermeasures [RCM] very important to the 
operational planners. 

The main body of this report is divided into 
sections in which RCM in the Air Forces, Navy, 
and Ground Forces are discussed separately.^ 
This chapter covers the use of radio and radar 
countermeasures both in the European and in 
the Mediterranean Theaters of Operations. In 
this introductory section, a brief summary of 
the early activities of the RAF is given since 
it was this early experience in RCM which to a 
great extent was the basis for commencing the 
countermeasures program by the U. S. Armed 
Forces and developmental laboratories. The 
operational need for RCM and the extent of the 
aid given by civilians to the Armed Forces in 
the theater are discussed. 


14 2 EARLY BRITISH USE OF RCM 

The earliest known use of radar by the Ger- 
mans was in 1939. The importance of counter- 
measures was first brought home in World 
War II during the German raids on England in 

a Much of the material concerning RCM in the 
European Theater of Operations [ETO] is also to be 
found in reference 831, which refers particularly to the 
activities of the American-British Laboratory [ABL] 
in connection with the countermeasures program. 


1940 and 1941. It is pertinent in this report, 
which deals with the use of countermeasures by 
the U. S. Armed Forces, to give a brief history 
of the use of RCM by the British prior to their 
use by the United States. 

After the fall of France, when the Germans 
commenced the Battle of Britain with heavy 
bomber raids on British cities, the Germans set 
up a large number of navigational systems 
which were designed to aid in the bombing of 
England at night. It has often been stated that 
radar played a very large part in the successful 
defense of Britain against the day attacks by 
which the Luftwaffe first tried to bring England 
to her knees. When the Germans switched to 
night bombing, countermeasures which were 
applied against the navigational systems used 
by the Germans in these night raids were a very 
important factor in reducing the severity and 
effectiveness of the bombing. 

The German successes in France, the Low 
Countries, and Norway made it possible for 
them to lay navigational beams across English 
targets from a very broad front. The RAF 80th 
Wing was given the responsibility for counter- 
ing these navigational systems. Listening sta- 
tions were maintained along the coast to search 
for new navigational beams and new frequen- 
cies and to locate the stations from which these 
systems originated. A great deal of information 
concerning the target selected by the enemy for 
a particular night was obtained from a study 
of these signals. Information from these listen- 
ing stations was immediately transmitted to a 
central point where the decision was made as 
to the type of jamming to be used. 

The Germans originally used fixed medium- 
frequency beacons and Knickebein, which was 
a Lorenz-type beam on 10 m which used the 
blind approach equipment installed in every 
German night bomber. Later on the Electra, 
Ruffian, medium-frequency direction-finding 
[DF] stations, and the Benito systems came 
into use. The Electra was a medium-frequency 
Lorenz beam, whereas the Ruffian was a more 
complicated Lorenz system on 70 me with two 


264 


EARLY BRITISH USE OF RCM 


265 


crossbeams giving fine range. A few of these 
navigational systems were jammed in various 
ways — for example, with jammers which 
emitted signals very nearly like those of the 
system being jammed. The DF systems, how- 
ever, were rendered ineffective by the use of 
''meaconing.” The ground meacon station picked 
up the German aircraft transmission on which 
a DF bearing was being taken and retrans- 


The first use by the British of radio com- 
munications jamming occurred in the Libyan 
campaign which commenced on November 18, 
1941. During this operation, the British 
equipped six Wellingtons with 50-w trans- 
mitters to jam the German tank radio equip- 
ment, which operated on a frequency of 27 to 
33.5 me. Preliminary tests indicated that all 
enemy voice and code communications between 



Figure 1. Small German Wurzburg — the principal German radar used for antiaircraft fire control. 


mitted it from a point several miles distant 
from the receiving site. The bearing could 
thereby be thrown considerably off, and there 
have been a number of cases where German 
aircraft were so confused that they landed in 
England thinking they were in Germany. Con- 
siderable success attended all of these counter- 
measures operations, the enemy crews very 
often complaining that their sets were out of 
order and repeatedly requesting DF fixes from 
the ground stations. 


points which were more than 2 miles apart 
would be prevented within a radius of 30 miles 
of a jamming aircraft at 15,000-ft elevation. 
Prisoners stated that they were usually out of 
voice or telegraph communications after these 
operations were commenced. Unfortunately, 
however, it is impossible to know exactly what 
were the results of this program because a few 
days after its initiation all planes involved in it 
were lost. 

The Bruneval raid of February 28, 1942, was 


266 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


primarily undertaken to capture an operating 
German radar station in order that knowledge 
concerning the state of developments reached 
by the Germans in radar might be obtained and 
to determine the specific characteristics of the 
German Wurzburg radar equipment which was 
installed at Bruneval. At that time, the Wurz- 
burg appeared to the British as a potentially 
increasing threat because of its possible use in 
controlling searchlights and antiaircraft fire, 
and as ground-controlled-interception [GCI] 
equipment. A major portion of the equipment 
except the indicator system at Bruneval was 
carried away bodily and suffered very little 
damage. It was later possible to make the units 
work in the laboratory at Telecommunications 
Research Establishment [TRE] without modifi- 
cation or reconstruction. From these tests, a 
great deal of information concerning the equip- 
ment was obtained, making it possible to design 
jamming equipment much more successfully. 
This information was of great interest to the 
laboratories in the United States which were 
preparing development of countermeasures 
equipment, with inadequate information con- 
cerning the enemy radar and tactics. 

One incident which served to accelerate Allied 
interest in the development of radar counter- 
measures was the German jamming of the Brit- 
ish radar system which occurred during the 
Schaimhorst and Gneisenau actions. These 
ships were berthed at Brest in Brittany, France. 
The British were very anxious not to let these 
ships go across the Channel or around England 
to the northern part of Germany, where they 
would be a potential threat to Allied shipping. 
No official history of this action is available, 
but from informal reports it appears that before 
the day set for the move German jammers had 
interfered spasmodically with the British radar 
system. The British operators did not recognize 
that the jamming was genuine, or if they did 
they were not greatly concerned because no 
unusual operation was connected with the jam- 
ming. One day in bad weather all the German 
jammers which had previously been tuned and 
set on the proper frequencies, jammed all the 
British radar systems of which the Germans 
had knowledge. It is not known whether the 
air-to-surface-vessel [ASV] radar of the British 


patrol planes, which were supposed to determine 
whether the ships left the port of Brest, were 
also jammed because most of the planes were 
lost. The fact is that the ships were not detected 
until after they had come around the Brittany 
peninsula and were well on their way through 
the channel. 

Some of the British radars noted the unusual 
German air activity which, unknown to the 
British, consisted of aircraft escorting the 
ships, but because of organizational difficulties 
no attention was paid to these aircraft until a 
British naval aircraft saw the ships and sent 
an urgent alarm. Air attacks were hastily or- 
ganized and the Dover coastal batteries in- 
formed, but it was too late. Many of the old 
Swordfish torpedo planes which attacked the 
ships were lost but little if any damage was in- 
flicted on the German ships. This operation was 
indeed a warning to the British, who at that 
time had 60 per cent of their radar on one fre- 
quency and were therefore extremely vulner- 
able to enemy jamming. It also made high-level 
authorities and officers aware of the danger of 
countermeasures and spurred the effort of both 
British and American research establishments 
in the search for effective countermeasures and 
antijamming [AJ] devices. The Scharnhorst 
and Gneisenau action can be considered a turn- 
ing point in the history of countermeasures. 
After that there was no question that deter- 
mined effort was necessary in the development 
of countermeasures which had been proved so 
effective when used against Allied sets. Paral- 
leling the development effort, a training pro- 
gram for radar operators was also initiated to 
alert operators against the dangers of jamming 
and to teach them to distinguish intentional 
enemy jamming from defective operation of 
their sets. 

The British first used radar jammers to jam 
the German coastal radar which was being 
employed by the enemy against Allied shipping 
in the Strait of Dover. The jammers were lo- 
cated on the Dover Cliffs and used railing 
(pulse) type modulation. 

Towards the end of 1942, a very different 
type of RCM was employed by the British 
against the German 120-mc early-warning 
[EW] radar. It is described here in some detail 


SCOPE OF OPERATIONAL USE OF RCM BY U. S. ARMED FORCES 


267 


because it is important to show that there is 
more to RCM than jamming and search. This 
operation was carried on by Moonshine equip- 
ment, which was an airborne radar counter- 
measure by means of which a few planes appear 
to the enemy radar as a large raid. The Moon- 
shine is designed to increase the amplitude and 
duration of the echo returned from the air- 
craft, thus making it appear to the radar that 
many more aircraft are present. Such equip- 
ment was used on several occasions where a 
diversion was required, especially in support 
of Eighth Air Force raids, and was also em- 
ployed by the RAF fighter command in an 
attempt to bring up enemy fighters. During 
this period, enemy fighters avoided conflict ex- 
cept on highly favorable terms when Allied 
bombers were sent over. Fighter sweeps by the 
British were generally unsuccessful and Moon- 
shine was used in an attempt to improve their 
success. The adoption by the Germans of their 
550-mc Wurzburg equipment for EW caused 
the use of Moonshine, which had not been 
developed for use on that frequency band, to 
be dropped. The British were afraid that the 
use of Moonshine would be compromised if 
the Germans were able to check up on the size 
of the raid by the use of the Wurzburg. In a 
normal Moonshine operation, eight Defiants 
flew with a fairly large group of fighters in 
towards the enemy coast. When approximately 
30 miles away, the Defiants left the fighters, 
dropped down nearly to sea level, and proceeded 
home at a very low altitude, where they escaped 
radar detection. The effectiveness of Moonshine 
was never completely determined and since a 
large number of fighters were always sent with 
the bombers it was never certain whether the 
use of Moonshine was a particularly important 
factor in causing the Germans to believe that 
a large raid was approaching. 

After the RAF night raids were started the 
British became greatly concerned over the use 
by the enemy of ground radar for the control 
of night fighters, antiaircraft fire, and search- 
lights. The Freya radar at that time was the 
equipment most used by the Germans against 
the RAF, although later the Wurzburg became 
an important part of the German defenses. The 
British designed and built an airborne jammer 


which was known as Mandrel to cope with the 
Freya radars. The Mandrel was the first jam- 
mer which used noise modulation and was used 
with considerable success throughout the rest 
of World War II. 


3 SCOPE OF OPERATIONAL USE OF 
RCM BY U. S. ARMED FORCES 

Radar countermeasures played a consider- 
ably more important part in World War II than 
radio countermeasures. Radar countermeasures 
were of more importance to the U. S. Army Air 
Forces than to any other branch of the Armed 
Services, since the enemy radar was used 
against our aircraft to a considerably greater 
extent than against any other type of attack. 

Heavy bombing was commenced by the 
Eighth Air Force in August 1942, and in the 
North African campaign in early 1943. Blind 
bombing was started by the Eighth Air Force 
in November 1943 and from then on was used 
in many of the raids. After this, approximately 
55 per cent of all Eighth Air Force attacks were 
made during blind bombing conditions. Radar 
countermeasures were of greatest use to the 
Air Force during such attacks, because the 
enemy was forced to rely entirely on radar for 
flak-control information during such operations 
and did not have visual range- and direction- 
finding methods to fall back on. 

For reasons that will be explained in a later 
chapter, countermeasure techniques were not of 
great value in solving the fighter problem. 

Heavy bombing was commenced against 
Italian targets in the fall of 1943 from bomber 
bases located in North Africa. At the beginning 
of 1944, the Fifteenth Air Force was formed 
and, when strategic bases were developed in 
Foggia, the heavy bomber offensive was made 
considerably more effective. The problems of 
the Fifteenth Air Force, in so far as RCM was 
concerned, were quite closely allied to those of 
the Eighth Air Force, since both air forces 
were attacking a common enemy and in some 
cases were even attacking the same target. 
There were certain differences between the 
radar equipments and techniques used in the 
Italian Theater and those used in Germany, 


268 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


since in general the Germans concentrated their 
best type of radar and largest numbers of 
equipment within the homeland. The similari- 
ties were such, however, that in this report no 
attempt will be made to duplicate discussion 
of RCM problems which apply equally well to 
both theaters. 

The strategic air forces made far more ex- 
tensive use of RCM than did the tactical air 
forces. There were two reasons for this. The 
first was that the tactical air forces, by the 
very nature of their job, ordinarily attacked 
targets which were not as well protected in 
terms of guns and radar equipment as the 
heavily defended strategic targets. Secondly, 
the size of the medium bombers made the use 
of additional RCM equipment, which was often 
bulky and sometimes required an operator, 
rather difficult to handle. Very little use was 
made of electronic jammers by the Ninth, First 
Tactical, or Twelfth Air Forces. All three air 
forces, however, made considerable use of the 
confusion reflector. Window. 

As previously stated, countermeasures were 
not used to a large extent by the ground forces ; 
however, there were a few cases in which coun- 
termeasures were employed, such as during the 
battle of the Ardennes when aircraft of the 
Eighth Air Force were used to carry jammers 
over the battlefield to interfere with enemy 
tank communication. 

Radar countermeasures were used exten- 
sively by the Navy, whose units conducted 
search, for instance, against enemy submarines 
and used RCM as a means of protection against 
enemy detection and radar-controlled fire. 
Radar deception was used as a powerful weapon 
in many operations. Also, RCM was used with 
apparent success against the enemy guided 
missiles. 


^ U. S. CIVILIAN AID TO THE 
ARMED FORCES 

In the spring of 1942 the director*^ of the 
Radio Research Laboratory [RRL], went to 
England to study the British RCM program. 
His findings were of great importance in deter- 
Dr. F. E. Terman. 


mining the initial direction that was taken by 
the American RCM program. 

Since our own Air Forces had not at that time 
commenced operation in the field, it was only 
natural that most of the thinking was devoted 
to the types of problems and solutions that were 
of concern to the RAF. In November 1942, six 
junior scientists from RRL and Radiation Lab- 
oratory [RL] were sent to work in the British 
RCM laboratories for a period of about 6 
months in order to become familiar with the 
work that the British were doing. The Ameri- 
can Air Forces, during this period, found that 
they needed help in the countermeasures field, 
and, since no American facilities were available 
in the theater, they turned to the British for 
assistance, particularly to the Royal Air Force 
and to TRE. The latter assigned one of the 
American research men to the Eighth Air 
Force, but at the same time they felt that this 
American radio countermeasures effort in the 
operational theater was disproportionately 
small when such a large effort and so much 
manpower were available in the United States. 
As a result of this need and the observation 
of a mission of United States scientists, the 
American-British Laboratory (see Figure 2) 
was set up in August 1943, through a contract 



Figure 2. The American-British Laboratory, 
Great Malvern, England, which operated under 
contract OEMsr-1045 from Division 15 of the 
National Defense Research Committee. 

from Division 15 of the National Defense Re- 
search Committee with Harvard University. 
This laboratory was set up to aid the U. S. 
Armed Forces in the European Theater of 


RCM IN THE U. S. AIR FORCES 


269 


Operations [ETO] in their use of RCM equip- 
ment and techniques. The laboratory grew to 
about 70 people and remained in operation until 
the end of the war in Europe. This laboratory 
engaged in work for practically all branches of 
the U. S. Armed Forces, including the Navy, 
the Air Forces, and the Ground Forces. 

No civilian laboratory was ever set up in the 
Mediterranean Theater of Operations [MTO]. 
Instead, a number of civilian technical observ- 
ers were sent from RRL to aid the Air Forces 
in the use of RCM. The first of these observers 
arrived in the MTO in April 1943, when the 
RCM program was being started. A total of 17 
technical observers from RRL or ABL-15 were 
sent to the MTO, and at the end of World War II 
seven men were stationed with the Fifteenth 
Air Force or with MAAF to help with RCM 
problems. 


5 RCM IN THE U. S. AIR FORCES 

14.5.1 rpRg Operational Problem 

After the beginning of daylight bombing, the 
German defenses consisted of daylight fighter 
attacks and of antiaircraft artillery. The fighter 
threat was particularly serious at the begin- 
ning, so much so that at the end of 1943 the 
Eighth Air Force had to limit its activities for 
two or three months to shallow penetrations 
until long-range fighters became available. (At 
this time, the Fifteenth Air Force had just been 
formed from the heavy bomber groups of the 
Twelfth Air Force.) 

Starting in February 1944, a full-fledged 
offensive began against the Luftwaffe, both by 
bombing of aircraft factories and by aerial 
combat. From March 1944 on, the whole strat- 
egy became one of engaging the enemy aircraft 
under any circumstances, favorable or unfavor- 
able, with the purpose of shooting down as 
many as possible. This strategy influenced the 
countermeasures activities in support of the 
strategic air forces, because no requirement 
then existed for preventing the enemy from 
knowing the time, direction, and target of our 
attacks. Heavy losses due to fighters were suf- 
fered by the AAF in early 1944 ; but thereafter 


the fighter losses decreased continuously as is 
shown in Table 1, taken from Eighth Air Force 
operations. 

It will be seen that, although fighters were 
responsible for the major losses in 1942 and 
1943, during the remainder of World War II 
the flak problem became the more serious. The 
increase in losses towards the last part of the 
war is, of course, due to the increased weight 
of attack and does not represent a greater per- 
centage of losses. Although not shown in this 
table, the number of enemy aircraft shot down 
increased continuously, and at the same time 
the number of operational sorties by the enemy 
decreased, presumably because of lack of oil 
and trained pilots. 


Table 1. Eighth Air Force Losses,* 


Period 

Lost to flak 

Lost to flghters 

Aug 1942 to Jan 1943 

5 

25 

Jan 1943 to July 1943 

166 

500 

July 1943 to Jan 1944 

165 

518 

Jan 1944 to July 1944 

847 

637 

July 1944 to Jan 1945 

1,320 

438 

Jan 1945 to end of 
World War II 

248 

92 


* Figures only approximate. 


The threat created by the German fighters 
against the strategic bombers based in the MTO 
became particularly serious when the heavy 
bombers went to bomb targets in Germany. 
However, the distance between the front lines 
and the targets was such that no effective 
jamming of the enemy EW system could be 
conducted with any hope of substantially de- 
creasing the fighter threat for the deep pene- 
tration missions. In the MTO, as in the ETO, 
after the fall of 1944, flak was by far the major 
cause of loss due to enemy action. 

Flak RCM 

With the progress of our ground forces, the 
area to be covered by the available enemy flak 
guns decreased steadily and the density of the 
enemy flak defenses increased correspondingly 
until at the end of 1944 as many as 15,000 
heavy guns had been counted on the German- 
controlled territory. 

Fighting against flak guns is a difficult task, 
and, whereas tactical air forces (particularly 


270 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


the Twelfth Air Force) occasionally bombed 
flak batteries with some success, the strategic 
air forces had to rely mainly on passive de- 
fenses and on radar countermeasures. To the 
men responsible for deciding the operational 
tactics of the Eighth and Fifteenth Air Forces, 
several possibilities were presented as a means 
of decreasing the flak risk. One of them was 
RCM, about which this report will deal spe- 
cifically. However, the picture as a whole should 
first be presented in order that any single aspect 
may then be seen in proper perspective. 

The type of formation flown and the way 
these formations navigated, especially near the 
target area, very greatly influenced the flak 
risk to which the bombers were exposed. In the 
early months of 1944, the bombers were flying 
in squadrons or boxes of 18 aircraft, and fre- 
quently three of these squadrons were flying 
together, so that it was often possible to see 
combat wings or attack units of 54 aircraft. The 
reason for this was that guns in the bombers 
were the only defense against enemy fighters 
and crossfire protection was necessary for an 
effective defense. Formations of this size were 
very unwieldy and required high skill on the 
part of the pilots. Furthermore, they were the 
ideal targets for a flak battery. The reason for 
this is clear; if a shell is aimed at the center 
of a combat wing of this size, it can hardly 
miss even if the aiming error is relatively great. 
Decreasing the size of the formation was, there- 
fore, the first aim as soon as the losses from 
flak began to exceed those from fighters. This 
could be done only to a limited extent because 
making maximum use of the few available blind 
bombing devices had led to the technique of 
dropping bombs with only one sighting oper- 
ation made by the lead bombardier. The neces- 
sity of any significant reduction in the size of 
the formation was delayed until July 1944, and 
even then the size of the squadron still remained 
far from ideal. 

Another method of reducing the flak risk is 
to increase the concentration of attack so as to 
have as many aircraft as possible fly over the 
target in the minimum time. Formation flying 
is a difficult business, as prop wash and con- 
densation trails prevent squadrons from flying 
too close together. These difficulties were con- 


sidered very important. Despite this, all possi- 
ble efforts were made to increase the concen- 
tration as much as possible and several wings 
in the 8th and 15th Air Forces tried special 
tactics with some success. 

Evasive action has been long recognized to be 
a very effective countermeasure against flak 
and the same can be said of downwind flying 
(to increase the relative ground speed) ; but, 
although these methods decrease the flak risk, 
they bring about a loss in bombing accuracy. 
This means more bombers or more missions are 
needed to do the same job. For these reasons, 
no evasive action was taken by the strategic 
bombers although bombing was often done 
down wind. Armor plate and other devices could 
be designed to reduce the vulnerability of each 
bomber, but in the ETO the increase in weight 
and the nonavailability of the necessary equip- 
ment prevented this trend from going very far. 

Altogether, therefore, from the point of view 
of the strategic air force, flak remained a threat 
against which it was difficult to take positive 
countermeasures. For this reason, the possibil- 
ity of using RCM was very favorably consid- 
ered, even if some doubts existed as to its 
effectiveness in visual missions. The problems 
inherent in the installation of a large number 
of RCM sets in some 5,000 aircraft and in the 
use of a proportionally large number of bundles 
of Chaff appeared less difficult than changes in 
the long-established operational techniques em- 
ployed up to that time. 

Another consideration which made RCM at- 
tractive was that reduction in the ffak risk 
would enable operational planners to assign 
lower flying altitudes to the bombers without 
undue increase of the danger to which the air- 
craft would be exposed. With the decreased 
altitude, a higher bombing accuracy would be 
obtained, and therefore the number of sorties 
required to knock out a target would be pro- 
portionately reduced. 

The tactical air forces in the ETO and MTO 
did not make important use of electronic jam- 
ming. Although there were early experiments 
with Carpets in the Ninth Air Force, these were 
on a very small scale and could not have been 
an important factor in influencing losses. 

The strategic air forces were always given 


RCM IN THE U. S. AIR FORCES 


271 


priority on RCM equipment, and it was not 
until early 1945 that Carpets became available 
in quantity to the tactical air forces. At that 
time the possibility of using Carpets was con- 
sidered by the bombardment division of the 
Ninth Air Force, but for a number of reasons, 
including the fact that the air force was in the 
process of shifting from B-26's to A-26’s, it 
was decided not to use electronic jammers. 
Henceforth, consideration of RCM assistance 
for the tactical air forces involved the integra- 
tion of either spot- or bar rage- jamming instal- 
lations into an A-26 aircraft. Because of the 
small crew complement of this aircraft, manual 
spot- jamming installations were ruled out. Even 
if space and weight had been available to carry 
transmitters, receiver, and operator (an addi- 
tional load which probably could not have been 
accommodated), it would not have been desira- 
ble to add an additional man to a two-man 
crew, since the resulting 50 per cent increase 
in crew complement might have resulted in in- 
creased personnel casualties even if aircraft 
had been saved. Barrage-jamming calculations 
undertaken independently in the field and at 
the laboratory indicated that at best no more 
than 30 to 40 per cent of the dangerous radars 
could have been covered. This conclusion was 
based on Ninth Bombardment Division opera- 
tions, where the maximum force to be consid- 
ered as a unit for self-protection was the 
16- to 18-plane box. Thus, protection from 
one-third of the dangerous radars was not con- 
sidered sufficient to warrant the effort of bar- 
rage installations, because of the small number 
of aircraft whose loss could be attributed to 
radar-controlled flak fire. Spot jamming would 
obviously have provided better protection to 
the medium bomber forces with considerably 
less effort, but space and weight limitations of 
the A-26 aircraft ruled out such a plan. 

Repeated requests for the numerical evalu- 
ation of the effectiveness of RCM were made to 
the RCM civilian personnel both in the ETO 
and the MTO. A great deal of work was done 
in attempting to answer these requests. After 
some already elaborate analysis, a coordinated 
effort was begun in the Eighth Air Force to 
analyze the battle damage figures in a way 
which would take into account the effect of 


almost all of the important parameters. The 
result of this work was unsatisfactory and no 
numerical evaluation of the effectiveness of 
RCM could be supplied. The battle damage fig- 
ures proved to be too inconsistent to allow 
drawing definite conclusions. In the MTO, on 
the contrary, work conducted on similar, even 
if less thorough, lines, appeared to give more 
consistent results, at least during the summer 
and fall of 1944. It was, of course, definitely 
established that RCM was effective and an 
attempt was made to measure quantitatively its 
effectiveness. Because of the controversial na- 
ture of the comparison between the ETO and 
MTO methods of analysis, it is considered be- 
yond the scope of this report to summarize the 
results obtained in the MTO. It is sufficient to 
say that tests against captured equipment, the 
effect of radar countermeasures when employed 
against our own equipment by ourselves or 
the enemy, and the attempts by the Germans 
to develop AJ devices, together with intelligence 
reports, were actually the only definite proof 
available before V-E Day of the usefulness of 
the recommended tactics and RCM installations. 

Fighter RCM 

The effective defense of Germany and Ger- 
man-occupied territory by the enemy fighters 
was based on a well-developed radar network, 
very-high-frequency intercept stations, ground 
observer groups, spotter aircraft, and intercept 
stations which devoted their attention to special 
signals like Carpet or airborne radar. All these 
sources of information were coordinated and 
contributed to give to the headquarters of the 
enemy fighter defense a complete picture of 
the air attacks even before the bombers left the 
vicinity of their bases as well as during the at- 
tack itself. 

Control of the fighters from the ground sta- 
tions was carried on during the winter of 1944 
by means of h-f and v-h-f transmissions. In 
single-engine day fighters, very high frequency 
was used exclusively, the v-h-f equipment being 
used for normal voice communications and 
Benito control. It is clear that interfering with 
enemy communications, especially with the air- 
to-ground and ground-to-air channels, was a 
promising approach to defensive tactics. Jam- 


272 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


ming of communications, however, is intrin- 
sically much more difficult than jamming radars 
and it requires more powerful transmitters. 

Another approach to defense against fighters 
was to interfere with the radar network so as 
to decrease the amount of information available 
to the enemy controllers. Here again the multi- 
tude of frequencies used by the enemy for the 
purposes of early warning and the large net- 
work of radar stations existing along the Chan- 
nel, the Dutch coast, the Adriatic Sea, northern 
Italy, Yugoslavia, and inland made the problem 
of screening the bomber formation from radar 
detection difficult. 

Despite the difficulties of countermeasures 
against the radar network and fighter com- 
munications, the RAF managed to throw the 
enemy system out of balance successfully in a 
large number of operations. 

Tactics peculiar to the RAF made this pos- 
sible ; the RAF flew at night with single aircraft 
distributed along a bomber stream, so that less 
jamming power was required against the 
enemy radar and no visual ground observation 
was possible. A special group (slightly bigger 
than an American wing) was devoted by the 
RAF to countermeasures. Without going into 
details which would be outside the scope of this 
report, it might be mentioned that, altogether, 
they were quite successful against early warn- 
ing, GCI, and even aircraft interception [AI]. 
The reasons why such a program was never 
duplicated by the USAAF are simple and worth 
considering at this point. 

First of all, AI did not represent a menace 
to daylight bombers ; second, it appeared prac- 
tically impossible during daylight over enemy 
territory to create deceptions whereby one 
group of ten planes was made to look like a 
whole bombing raid. Furthermore, when fighter 
escorts became available, the intent of the air 
force was to meet and fight against the enemy 
aircraft, and therefore there was no desire to 
prevent the enemy from knowing the location 
of our bomber formations. Even in the late 
months of 1943 and the first two months of 
1944, when long-range fighter escorts were not 
present and the enemy fighters represented a 
serious menace, radio and radar countermeas- 
ures could hardly have been sufficient to protect 


the formations against fighter attacks in unes- 
corted deep penetration raids, which were the 
ones on which the danger was serious ; besides, 
the amount of RCM equipment available was 
extremely limited. 

Another reason which made it difficult to 
carry on an effective RCM program was that 
much useful intelligence could be gathered by 
listening to the enemy communications and 
here, as in most theaters of war, a conflict 
existed between the people who wanted to jam 
the enemy communications and the people who 
wanted to listen to them in order to get intelli- 
gence. 

To summarize, when the fighter menace was 
great, at the end of 1943 and the beginning of 
1944, the lack of equipment and the practical 
impossibility of carrying on fighter counter- 
measures from the available bases, limited the 
use of RCM by the American Air Forces as a 
means of protection against fighters. From the 
spring of 1944, the whole strategy against 
enemy fighters changed, and, despite the fact 
that more equipment had become available and 
new bases had been obtained, both radio and 
radar antifighter countermeasures were found 
to be inconsistent with the general operational 
doctrine of the strategic air forces. 

The above statement applies only to the jam- 
ming of the enemy EW radar network and the 
enemy communications systems ; other types of 
RCM work which were dictated by the chang- 
ing air situation were undertaken. For instance, 
at the end of 1944, it was found that the enemy 
was getting too much intelligence by listening 
to our v-h-f chatter and steps were taken by 
the Eighth and Ninth Air Forces to jam our 
own v-h-f frequencies during the assembly over 
England by means of aircraft which were flown 
close enough to the enemy listening stations and 
far enough from England to prevent the enemy 
H-Dienst (intercept system) from working 
properly, without interfering at the same time 
with the communications between our bombers 
and between the bombers and the ground. 

When the air supremacy was established in 
such a way that finding enemy fighters to fight 
against became a serious problem, work was 
started on building equipment capable of inter- 
rogating and DF-ing on the enemy identification 


RCM IN THE U. S. AIR FORCES 


273 


friend or foe [IFF] in order to guide Allied 
fighter groups on to enemy fighter concentra- 
tions. Furthermore, when at the end of 1944 
and at the beginning of 1945 jet planes ap- 
peared as a potential danger, work was started 
again in the ETO on a radar screen just as a 
measure of insurance in case the whole U. S. 
fighter strategy had to be changed. The work 
was done in the first month of 1945 along the 
same lines followed in the early months of 1944 
for the same purpose but in a better way. Ex- 
cept for a few days of operation which will be 
described later, this screen was never used and 
World War II ended before jet planes were ever 
used in large quantities by the enemy. 

The history of the whole effort against Ger- 
man fighter defenses by the U. S. Strategic 
Air Forces is one of uncertainty, with projects 
started and left not completed because of 
changes in the strategic situation. In this part 
of the RCM field more than any other, the im- 
portance of a close liaison between the opera- 
tional planners and the technical people appears 
fundamental. There is perhaps nothing more 
striking than the contrast between the RCM 
work carried on by the RAF, the largest part 
of which was directed against enemy fighters, 
and the RCM work carried on by the American 
Air Forces, which was almost entirely antiflak. 

Another type of work in which the RCM per- 
sonnel were involved both in the civilian lab- 
oratory and in the Strategic Air Forces was 
the problem of airborne interception of enemy 
communications. This was essentially a func- 
tion of intelligence; the intelligence sections 
of both the RAF and the Eighth and Fifteenth 
Air Forces did make use of the results obtained, 
but in the Eighth Air Force the technical side 
was handled by RCM personnel because of 
their experience with radar search and with 
techniques of a similar nature even if on dif- 
ferent frequency bands. In the Fifteenth Air 
Force, the technical side was handled by radio 
personnel, with a small amount of assistance 
from RCM personnel. 

The old problem of intercepting enemy com- 
munications for the purpose of gathering in- 
formation on the enemy order of battle and 
on the enemy reaction to bomber raids was 
started by the British Air Ministry, which de- 


veloped a very well-organized and smoothly 
operating organization which intercepted enemy 
transmissions and accurately DF-ed on them. 
Most of the intercept material available to these 
units came from ground receivers. It was clear, 
however, that ground reception did not give a 
clear picture of all the events inside Germany 
and, when the knowledge of such events was 
obtainable only through listening to the enemy 
v-h-f communications, airborne interception 
had to be employed. 


^ ^ Capabilities and Limitations of the 
RCM Available 

RCM officers and technical men working in 
RCM had two main lines of attack against 
enemy gun-laying [GL] radar. The first one 
was Chaff; the second. Carpets. Before giving 
details on these two countermeasures it must 
be noted that they act against the enemy radar 
sets in a completely different way. Chaff and 
Carpet have characteristics such that the com- 
bined use of the two at the same time presented 
the enemy with a problem which was much 
more serious than the one presented by the use 
of Chaff or Carpet alone. Actually, we know 
now from Intelligence, and we knew before 
from our own experience, that against a full- 
scale, well-organized RCM program of this type, 
the designer of the radar set has only one solu- 
tion: to build another set in a completely dif- 
ferent frequency range. The Germans attempted 
that but were too late. 

Chaff 

It is well known that a large quantity of 
Chaff can so infest an area that any aircraft 
flying near by is shielded against detection by 
any radar set whose frequency is near the one 
for which the Chaff is cut. If, therefore, our 
formations had been flying the ideal briefed 
course with all formations one behind the other 
in a continuous stream, only the leading forma- 
tion would not have had the full protection that 
the Chaff could offer. Unfortunately, especially 
on blind missions, the distance between the 
tracks of the different squadrons or groups 
was such that not more than 10 to 30 per cent 


274 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


of the aircraft participating in the mission flew 
close enough to the Chaff trails laid by preced- 
ing formations to take advantage of the full 
protection offered. 

In any case where a formation drops Chaff 
and is not near a trail, a skilled radar operator 
can often (still) track it by looking at the 
leading edge of the trail left behind. However, 


battery ; the inaccuracy increases when the 
amount of Chaff increases. Furthermore, when 
the target is being bombed by a force of, say, 
1,000 aircraft, the region over the target is so 
full of Chaff after the first 200 or 300 have 
gone by that it is extremely difficult for the 
operator to find a target even if he can track it 
once it is found. 



Giant Wurzburg used by the Germans for purposes of antiaircraft fire control and fighter 


Figure 3. 
direction. 

this operation requires a highly skilled crew, 
particularly in the case of the German Wurz- 
burg, which is not equipped with a plan-position 
indicator [PPI]. Furthermore, tracking of this 
type becomes more and more inaccurate when 
the target approaches the crossing poinU of the 

c Crossing point is, by definition, the point which is 
closest to the battery along the course of the aircraft, 
which is assumed to fly straight and level. 


In conclusion, it appeared, therefore, that 
two things could be done to improve the effec- 
tiveness of Chaff. The first one was to increase 
as much as possible the amount of Chaff 
dropped ; the second, to increase the concentra- 
tion of the attack, and at the same time to 
increase the precision with which each aircraft 
followed its predetermined track. 

Antijamming devices have been developed by 


RCM IN THE U. S. AIR FORCES 


275 


the Allies as well as the Germans which make 
it possible for a radar set to distinguish be- 
tween essentially stationary Chaff and actual 
moving targets. These methods are based on 
the fact that, with respect to the radar location, 
Chaff does not usually move at the speed of the 
aircraft. The doppler effect can therefore be 
used to find a moving target in a cloud of sta- 
tionary Chaff. It was natural to find the enemy 
reacting to our use of Chaff by developing AJ 
devices of this type. Increasing the amount of 
Chaff dropped was a partial answer but cer- 
tainly not a perfect one. It will be shown later 
that no such AJ device can work satisfactorily 
if effective electronic jamming of the type sup- 
plied by Carpet is present at the same time. 
This is one of the ways in which the combined 
use of Carpet and Window becomes more effi- 
cient than the use of either one alone. 

Chaff was packaged in bundles, each con- 
taining enough strips of aluminum to simulate 
either one or three heavy bombers, depending 
on the type of Chaff. In order to drop enough 
Chaff to simulate a continuous stream of air- 
craft, one “unit” of Chaff (one unit simulates 
one heavy bomber) must be dropped for each 
“round-trip pulse length” of the enemy radar. 
Since the German Wurzburg has a 2-psec pulse 
width, each aircraft should drop one unit each 
1,000 ft, about 5 units a mile, about 20 units 
a minute. In order to give an order of magni- 
tude of the quantity involved, if 20,000 sorties 
were flown in a month and the Chaff was 
dropped for, say, 20 min over the target area, 
8,000,000 units were required per month, which 
meant a total weight of about 600 tons of 
aluminum a month. 

Cakpets 

Three types of Carpets became available 
from the fall of 1943 to the end of World War II. 
The first, AN/APT-2, is better known as Car- 
pet I; the second, AN/APQ-9 (Carpet III), is 
more powerful than AN/ APT-2 but covers a 
more limited range of frequencies; the third, 
AN/APT-5, is still more powerful and covers 
a wider range of frequencies than either one. 
The APT-5 arrived in the ETO too late to be 
used in any significant quantity. The APT-2 
was the only set available in the first half of 


1944 and was rapidly replaced by the APQ-9 
when this became available during the fall and 
winter of 1944-45. 

Carpets, as well as most of the other elec- 
tronic jammers in use against enemy radar sets, 
can be used in two different ways, known as 
barrage jamming and spot jamming. In the 
former method, the Carpet frequencies are ad- 
justed so as to cover an enemy frequency band 
as evenly as possible with no holes in the bar- 
rage, whereas in the latter an operator with a 
receiver manually tunes the equipment to the 
enemy frequency. 

In the fall of 1943, a small number of Carpet 
Ps were available and the German sets occupied 
a frequency band from 560 to 580 me. Rough 
calculations and actual tests made in this coun- 
try showed that a barrage of Carpet Ps, with 
a spacing of about 1 me between adjacent 
carriers, could effectively shield 18 aircraft. 
This meant that if each aircraft in an 18-plane 
box had one Carpet, the frequency band covered 
could be made equal to the enemy’s frequency 
band. This procedure was followed in the two 
groups which could be equipped at that time. 

It is to be noted here that the basis for such 
a program was a certain number of aircraft 
per unit to be protected, a certain frequency 
band occupied by the enemy sets, and, finally, 
a certain spacing for one barrage. Any change 
in these three fundamental elements would 
have necessitated radical changes in the plan. 
Changes did come in all these three basic 
elements. As mentioned before, the size of the 
formation decreased ; the enemy, alerted by our 
jamming, took the obvious countermeasure of 
spreading the frequency band, and, finally, the 
more powerful APQ-9 set became available. 
Without a discussion of the intermediate steps, 
it can, therefore, be seen that a new situation 
arose at the end of 1944 with the enemy cover- 
ing a frequency band of 510 to 590 me and 
with the size of the squadron which was to be 
protected varying from 18 to 12, and some- 
times 9, aircraft. 

The problem of establishing a correct RCM 
plan was made difficult, notwithstanding the 
fact that with the new APQ-9 set and the 
smaller formations, spacing of IV 2 ^nd later 
2 me was shown to be acceptable. During the 


276 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


summer of 1944 the shortage of RCM sets had 
compelled the adoption of a spot-jamming pro- 
gram because, for obvious reasons, spot jam- 
ming is the system which enables the most 
efficient use of RCM sets to be made. In the 
month of September 1944 with the large num- 
bers of RCM sets available, a solution was 
found involving the combined employment of 
barrage and spot jamming in every group of 
the Strategic Air Forces. The details of this 
program and reasons which led to its initiation 
will be given later in this chapter. 

The important point here is the fact that any 
RCM program is very closely connected with 
the type of formation flown, the distance be- 
tween the different formations, the type of 
target that these formations are going to attack, 
and the enemy’s radar tactics. It is clear, for 
instance, that if a target is defended by ap- 
proximately 200 guns and the enemy has avail- 
able one radar set for each 10 guns, there is a 
maximum of 20 radar sets potentially danger- 
ous to this formation and possibly 10 which will 
be looking at the same time at each squadron. 
Furthermore, if squadrons are widely sepa- 
rated it is impossible to assume any mutual 
help between the jammers carried by one squad- 
ron and those carried by a following one. Con- 
sideration of factors of this type was necessary 
to establish the air force RCM plans. 

Some general considerations regarding the 
mutual advantages and disadvantages of bar- 
rage and spot jamming should be mentioned 
here. Barrage-jamming equipment is pretuned 
on the ground, does not need special operators, 
prevents the use by the enemy of small fre- 
quency changes to avoid the jamming signal, 
and is altogether a better system, but it requires 
a large number of sets and sometimes a pro- 
hibitive number when the enemy frequency 
band becomes too wide. Spot jamming is in 
principle a very efficient method but it suffers 
very greatly by the fact that the human element 
plays such an important part in its success. 
Furthermore, the introduction of an extra man 
in the crew of each aircraft produces opera- 
tional problems which are not always easy to 
solve. Finally, with spot jamming, there is 
always a danger that two or more operators 
may be jamming the same signal while another 


signal is tracking the formation undisturbed. 

The training given to the spot-jamming oper- 
ators in the average group of the Eighth Air 
Force was essentially a function of the interest 
shown by the RCM officer of that group in such 
a program. Spot-jamming operators were usu- 
ally gunners who represented surplus personnel 
because of the reduction in the crews of both 
B-17 and B-24 bombers from ten to nine mem- 
bers. Spot-jamming operators were given an 
initial training of 4 days in a course which 
was organized at the 36th Squadron. The in- 
telligence level of the students and the length 
of the course was such that it was impossible 
to expect a perfect job to be done. In the groups 
in which training was continued and intensified 
through the cooperation of the RCM officer, the 
efficiency level was reasonably high but it must 
be recognized that the quality of the personnel, 
overall, was insufficient to guarantee anything 
more than a mediocre performance. 

The above considerations point out an im- 
portant lesson, namely, that when the solution 
of a problem depends so much upon the human 
element, the same amount of attention should 
be given to the quality of the operating person- 
nel and to their training as is given to the 
development and construction of the actual set. 
Failure to do so, due to the lack of Military 
Occupation Serial [MOS] number or lack of 
Table of Organization [TO] openings under the 
Army organization, cannot but decrease the 
effectiveness of any even perfect effort on 
the part of the engineer who designs the equip- 
ment, installs it, and plans its operational use. 

One important limitation of electronic RCM 
is the following: The enemy could DF on the 
jamming signal, if he wanted to, and guess the 
altitude, which was relatively constant in the 
8th Air Force and 15th Air Force attacks. Then 
he could use this information"^ to do contin- 
uously pointed fire ; fire controlled through this 
procedure would not be so accurate as fire ob- 
tained with an un jammed radar, but it would 
still represent a serious danger. Admittedly, if 
a formation used Carpets and dropped Chaff at 


<1 Actually, in a predictor the operator can roughly 
determine the altitude by so “cranking in” range data 
as to make the altitude constant, even if he does not 
know its value. 


THE OPERATIONAL USE OF RCM IN THE MTO 


277 


the same time, the danger of D F-ing on the jam- 
ming signal would be greatly decreased, which 
is another reason why the combined use of 
Carpet and Chaff increased the usefulness of 
the total RCM effort. As a matter of fact, 
however, there appeared no real reason why 
the enemy could not turn off the transmit- 
ters, thereby eliminating the Chaff echoes, and 
use the angular information obtained from the 
jammer to control their guns. It is remarkable 
to note that all these fears were unfounded and 
that information gathered after V-E Day 
proved that the enemy did not resort to such 
tactics. On the contrary, emphasis was given 
in all the official documents to the requirement 
for the radar operators to try to ‘"read” through 
the jamming in order to locate the target. The 
reasons for this are not very clear. Actually, 
the enemy did rely on information obtained by 
DF-ing to plot the course of the formations; 
the same procedure, however — while inaccurate 
— would have been better than nothing in the 
control of fire, and ‘‘nothing” seems to have 
been obtained many times by the German oper- 
ators. 


^ THE OPERATIONAL USE OF RCM 
IN THE MTO 

Search and Investigation 

A knowledge of the technical characteristics 
of the enemy radar set is a necessary premise 
for any RCM program. For this reason, in 
the MTO, as in any other theater of war, RCM 
search and investigation began long before an 
effective offensive RCM effort was decided 
upon. The first Ferret aircraft with specially 
trained officers and one civilian observer from 
RRL was requested in late 1942, as soon as 
high-level operational officers became conscious 
of the existence of German radar and of its 
dangerous potentialities. The Ferret left the 
United States for North Africa about May 10, 
1943. At the time of its arrival, radar investi- 
gation in North Africa was being carried on 
by a few British aircraft of the 192nd Squad- 
ron. The coordination of the search activities 
of the U. S. and of the RAF aircraft was fairly 


easy. However, serious difficulties were en- 
countered by the personpel of the first Ferret 
and also subsequent Ferrets, because of the 
lack of a clear organizational setup for radar 
reconnaissance aircraft within the standard 
U. S. Air Forces organization chart. 

During the first month. Ferret aircraft de- 
voted their efforts to a search for enemy signals 
around Sicily, which was due to be invaded a 
short time later, specifically on July 9, 1943. 
These first flights were extremely useful in 
giving to the flying personnel experience in the 
determination of the best operating procedures. 
It was soon found that DF antennas were neces- 
sary and several attempts were made to im- 
provise some kind of satisfactory system within 
the theater. Actually the first Ferret had one 
Tail receiver capable of giving homing indica- 
tions, but the development of methods of 
pinpointing stations without flying straight in 
their direction was found necessary. Until 
developments, which started in the United 
States, were completed, both the British and 
American aircraft had to limit the scope of the 
search to the determination of the general posi- 
tion of the enemy stations, obtained by flying 
low and determining the point where the signal 
was strongest. This method, even if not com- 
pletely satisfactory, did give to the intelligence 
agencies a fair idea of the general deployment 
of enemy radar stations. 

It did not permit, however, the determina- 
tion of sites of enemy stations accurately 
enough to pinpoint them for the purposes of 
photographic reconnaissance. In a few cases 
stations were pinpointed with the Tail homing 
receiver mentioned above. 

Around the month of September 1943, the 
initial organizational difficulties involved in the 
establishment of a radar reconnaissance squad- 
ron were partially cleared. The Table of 
Organization of the Sixteenth Reconnaissance 
Squadron was used for the radar search air- 
craft and the squadron itself was put under 
the operational control of the headquarters 
MAAF. This setup was found satisfactory and 
lasted until the end of World War II. The 
squadron undertook the planning, flying, and 
analyzing of search missions ; but it also under- 
took general RCM work and powerfully con- 


278 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


tributed to the training of RCM personnel and 
modifications of RCM equipment. Until a large 
RCM program was established in the Fifteenth 
Air Force, the Sixteenth Reconnaissance 
Squadron remained the center of all RCM 
activities in MTO. 

Ever since the beginning of search activities 
in MTO, civilian technical observers from the 
Radio Research Laboratory of Harvard were 
attached to the squadron. Their presence was 
found extremely useful in bringing back to the 
home laboratory observational considerations 
for the improvement of the search equipment. 
These technical observers contributed sub- 
stantially to the success of the RCM program 
by assisting the Army units involved in the 
installation, planning, and use of the RCM 
equipment. 

Most of the personnel dealing with RCM 
problems all over the MTO, but especially in 
the Air Forces and in the Air Service Command, 
were originally trained in the Sixteenth 
Squadron. 

In March 1944, the first direction finder was 
installed in a plane of the squadron and flown 
on a mission. The results obtained were immedi- 
ately very good. More direction finders were 
ordered and later obtained. The work of the 
reconnaissance squadron was supplemented by 
ground listening stations, both British and 
American, and it can be stated that from the 
summer of 1944 on the combined results of all 
the investigational outfits contributed to pre- 
sent an almost complete and coordinated 
picture of the enemy radar situation. 

Of the ground stations, one was an American 
unit located in Corsica, known by the code 
name Beaver III, about which more will be 
said, the other two were British Noise Investi- 
gation Bureau listening stations, one of them 
located in Corsica and the other one in the 
eastern part of Italy. The two British listening 
stations were moved, after the invasion of 
southern France, to cover the Balkans and the 
northern part of the front, which had by that 
time moved around Bologna. 

A highly accurate DF and search ground 
station, called Ping Pong, built and operated 
by the British, was moved from England, where 
it had been used before the invasion of Nor- 


mandy, to Corsica, in August, and later to 
eastern Italy. 

With the beginning of a full-scale offensive 
RCM program within the 15th Air Force, two 
other sources of information became available. 
Operational bombers were equipped with 
search receivers and flown with trained per- 
sonnel to watch for the enemy reaction to 
Allied jamming and to investigate the enemy 
frequency distribution near the target areas. 
It must be noted in this connection that the 
work of the Ferrets and of the ground listening 
stations was by necessity limited to the investi- 
gation of early-warning and coast-watcher 
stations and that the gun-laying sets were 
usually beyond the range of investigational 
flight and of the ground receivers. 

The number of receivers available for this 
work was limited and only in August 1944 did 
the number of receivers available to the 
Fifteenth Air Force reach eight. Some of these 
receivers were used for search and later some 
for spot jamming. There were, therefore, 
enough to maintain the necessary program. In 
August, two groups were flying one or two 
aircraft equipped with search sets. The Twelfth 
Air Force also began to fly search receivers 
in August to check how important a threat 
enemy radar was in tactical operations. 

Beginning in September 1944, the type of 
jamming employed in the operational aircraft 
required the use of a receiver for the purpose 
of “setting on’' the jammer on the frequency 
of the enemy radar. The operators flying these 
spot-jamming aircraft were requested to keep 
a log of all the signals they heard. These logs 
supplemented the information obtained by the 
search receivers flown for the sole purpose of 
radar search in the operational bombers and 
contributed to the knowledge of the enemy 
frequency distribution. In addition to this, 
special recording receivers manufactured by 
the British were used. These receivers were 
known by the code name of Bagful. The Bagful 
tapes were used and analyzed periodically and 
the results obtained were coordinated with the 
results of the search missions and with the 
logs of spot-jamming operators. For instance, 
on two missions of October 1944, the tapes of 
the Bagful receivers indicated 25 signals track- 


THE OPERATIONAL USE OF RCM IN THE MTO 


279 


ing the formation and on another mission, also 
in October 1944, 23 sets appeared to track the 
formation on the bombing run. The results of 
the analysis of these tapes were very useful in 
order to impress upon the spot- jamming opera- 
tors the importance of a proper spot- jamming 
technique. They were, of course, also employed 
to determine the extent of the jamming cover- 
age that a formation would require on a heavily 
defended target. 

In July 1944 the first microwave receiver was 
flown operationally. Repeated missions did not 
disclose any definite signal which could not be 
traced to friendly sources. 

A means of defense against our jamming 
was to increase the spread of the operating 
frequencies of the enemy radar sets. Alerted 
by the jamming operations, the Germans took 
this obvious step. Search receivers, logs of spot- 
jamming operators, and Bagful tapes revealed 
during the summer of 1944 a large increase in 
the number of enemy signals between 510 and 
550 me. During the months of March and April 
1945, the same sources revealed another fre- 
quency band used by the enemy around 450 
to 460 me. These results had also been found a 
short time before in ETO. Although this spread 
of frequency made the problem of a proper 
planning of RCM operations more difficult, the 
availability of a large number of jamming sets 
and of improved Chaff which arrived in the 
theater during the fall of 1944 permitted 
successive expansions of the program which 
enabled the Air Forces to cope at least partially 
with the new threats. 

In the early months of 1944 another program 
was started to search for enemy communica- 
tions signals by flying German-speaking opera- 
tors in operational aircraft equipped with 
communication receivers. In April 1944, this 
type of operation was being conducted by one 
group. The information obtained was found 
useful by all of the intelligence agencies 
charged with the study of the enemy order 
of battle and determination of the enemy fighter 
reaction. Steps were taken, therefore, to ex- 
pand the program by ordering more equipment 
and by training more German-speaking per- 
sonnel. During the month of July 1944, about 
55 Radio-Telephone [RT] monitoring sorties 


were flown. The number of communication 
intercept sorties increased steadily until, at the 
end of World War II, about 25 sets were 
installed in bombardment aircraft and about 
150 monitoring sorties were flown every 
month. Beginning in the month of February 
1945, about 50 per cent of the sorties carried 
disk recorders, but, owing to the strategic situ- 
ation on the Italian front, many of these sorties 
did not intercept any enemy traffic at all. 

Flak Countermeasures 

Carpet 

Definite information that enemy radar was 
used during daylight operations was gathered 
during the middle of 1943. Fortunately, a 
limited number of jamming sets designed to 
meet RAF needs was available to the USAAF. 

The first plan for the employment of these 
sets in MTO was made before the invasion of 
Sicily, which took place in July 1943. Thirty- 
five B-17 aircraft were scheduled to jam the 
enemy EW systems on the approaches to Sicily ; 
each aircraft was scheduled to carry one 
Mandrel, to jam EW sets, and one Carpet, to 
jam GL sets. Only four of these jamming air- 
craft arrived in time for the operation and 
flew the mission as planned. Another offensive 
RCM operation was planned on September 8, 
1943, to cover the landing of airborne troops 
around Rome at the time of the Italian sur- 
render. This radar screen was planned to 
consist of 14 aircraft carrying two Mandrels 
each, plus six aircraft carrying two Carpets 
each. As is well known, the operation was 
cancelled, but the six bombers of the screen 
equipped with two Carpets were assigned to 
the 97th Bomb Group, which was part of a 
strategic bombing air force and became the 
first operational bomb group equipped with 
RCM. At the beginning of the month of 
November 1943, 14 aircraft were equipped with 
Carpets ; some of them had only one Carpet per 
aircraft. At that time, the North African 
Strategic Air Forces began to operate in south- 
ern Germany, and the losses from enemy flak 
became larger. The need for countermeasures 
against radar-controlled flak was therefore 
keenly felt. 


280 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


The first results obtained from flying Carpets 
in the 97th Bomb Group were highly satisfac- 
tory; the crews were very enthusiastic about 
the results. After the success of these early 
operations, a large-scale RCM program was 
formulated within the Fifteenth Air Force and 
the first requisition for a large number of 
jamming sets was placed. At the same time, a 
training program was started in the 16th 
Reconnaissance Squadron to prepare the in- 
stallation teams and train officers in the han- 
dling of RCM sets. However, the amount of 
equipment which became available during a 
good part of 1944 was not sufficient to expand 
the RCM program greatly. For instance, it was 
necessary to wait until March 1944 before the 
first shipment of 40 supplementary Carpet 
transmitters arrived in the theater. In the 
belief, however, that the necessary quantity of 
RCM equipment would arrive in time, the train- 
ing of installation teams continued; unfortu- 
nately, these hopes were to remain unfulfilled 
until the fall of 1944. 

During the spring and summer of 1944, the 
shortage of equipment prevented the planned 
expansion of the installation of electronic RCM 
equipment. This was very important because 
at the same time the enemy flak was becoming 
more and more dangerous and the enemy, 
alerted by the jamming, had begun to spread 
his frequency band. With the limited number of 
sets available, even in the groups equipped 
with them no satisfactory barrage could be 
planned to cover the whole enemy band. In 
August 1944, it was decided to use the Carpet 
jammers with greater efficiency by equipping 
a few aircraft with three transmitters and 
one receiver each, with a spot- jamming op- 
erator flying in the aircraft who would listen to 
the enemy signals and tune the transmitter to 
them. This first spot-jamming effort appeared 
very successful and encouraged the 15th Air 
Force to request a large amount of RCM to 
make it possible not only to expand the barrage 
jamming already planned but also to add 
further spot-jamming aircraft in the group. 

The situation as it existed in the month of 
October 1944 can be summarized by saying that 
of 21 groups, 6 had barrage installations, 3 had 
a few spot-jamming installations, and only one- 


third of the Air Forces had any electronic RCM 
at all. 

The month of October can be considered a 
turning point in the availability of Carpet 
equipment. During that month. Carpets arrived 
in large quantity, and installation was started 
in 15 groups. Schools were started to train new 
installation teams because the teams trained in 
the early part of the year were no longer 
available. The work of installation expanded 
rapidly. Moving vans were established to go 
from group to group to explain RCM, train 
personnel, and install equipment. In the early 
days of November 1944, the return of an 
observer from a trip to England brought to 
the 15th Air Force a great deal of information 
on the RCM program of the 8th Air Force. The 
importance of dual barrage installations (each 
aircraft carrying two Carpets instead of one, 
pretuned on the ground), to cope with the 
increased spread in the enemy frequency band 
and the small formations flown, was recognized 
and definite steps were taken to bring the MTO 
program to coincide more or less with the 
similar program carried on in the ETO. How- 
ever, the lack of military and civilian personnel 
made it imperative to complete first the single 
barrage (one Carpet per aircraft) and the 
spot- jamming programs which were well under 
way and to give to the dual barrage installa- 
tions a lower priority. It can be said that, as 
a result of the delay in the shipping of sets 
and of the shortage of qualified personnel, the 
RCM program in the Mediterranean followed 
very much the same trend as in the ETO but 
was about 2 to 3 months behind. As in ETO, 
the program for the ultimate solution, formu- 
lated during November and completed just at 
the end of World War II in May 1945, called 
for ten spot-jamming aircraft per group, with 
all the other aircraft in the group carrying 
barrage with dual installations (i.e., two jam- 
ming transmitters per aircraft, pretuned on 
the ground). The months of January, Febru- 
ary, and March 1945 saw the RCM program 
in the Fifteenth Air Force progressing at great 
speed. 

Personnel, both civilian and military, made 
periodic trips to all the groups, giving informa- 
tion to all personnel, from generals down, on 


THE OPERATIONAL USE OF RCM IN THE MTO 


281 


the capabilities and limitations of RCM. The 
number of aircraft equipped increased steadily. 
In February, about 600 aircraft had either 
single or dual barrage, and 100 aircraft had 
spot jamming. February 1945 was the first 
month in the history of the Fifteenth Air Force 
when every group had some kind of electronic 
jamming. From that time on, the number of 
dual barrage installations increased, and, of 


It might be noted here that the new jamming 
transmitter APT-5 was used in many of the 
spot-jamming installations. Altogether, more 
than 100 APT-5’s had been installed. 

It must be noted that the Fifteenth Air Force 
used a type of frequency distribution in its 
barrage which was substantially different from 
the one used in ETO. Formations flown con- 
sisted usually of boxes containing six or seven 



Figure 4. Radio Research Laboratory technical observer instructing flight personnel of the Fifteenth 
Air Force in the offensive use of radar countermeasures. 


course, the number of single barrage installa- 
tions decreased, so that by the middle of April 
there were about 624 aircraft with dual bar- 
rage installations, and 163 with single barrage 
installations. The spot-jamming program had 
also been practically completed. Two hundred 
aircraft were equipped with spot- jamming 
transmitters and the necessary receivers; they 
were distributed among the groups on the basis 
of eight to ten spot- jamming aircraft per group. 


aircraft each. Two boxes made an attack unit. 
Two attack units made a group. In days of 
maximum effort, a group actually consisted of 
two attack units of three boxes, instead of two 
attack units of two boxes each used in days of 
normal effort. In any case, both in the days 
of normal effort and in the days of maximum 
effort, the distribution of barrage frequencies 
was such that one box had its transmitters 
tuned to all the odd frequencies of the enemy 



282 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


h-f band, and another box had the transmitters 
tuned to all the odd frequencies of the enemy 
low band. The third box had the even fre- 
quencies of the high band, the fourth box had 
the even frequencies of the low band. In such 
a way, if all the boxes flew close enough to- 
gether, most of the enemy band was barraged. 
If only two boxes flew together, the whole 
enemy frequency band was still covered but 
with a much thinner jamming. 

In January 1945, the needs of MTO, with 
the difficulties encountered in this theater in 
the installation and operation of the very large 
RCM program, were recognized by the authori- 
ties in the United States and steps were taken 
to improve the situation. The cooperation be- 
tween ETO and MTO was improved by pro- 
moting exchange of visits between ETO and 
MTO civilian and military personnel. Three 
members of the ABL, which had been assisting 
the 8th Air Force, were sent to the Mediter- 
ranean to help the program there. 

Beginning in the summer of 1944, informa- 
tion was transmitted between the two theaters 
and the United States by means of teletype 
conferences. Problems were discussed infor- 
mally and solutions common to the two 
theaters were suggested. However, the lack of 
a coordinated laboratory in the MTO, like the 
one established in England, had a harmful 
effect on the speed of the RCM work. The 
limited personnel available was thoroughly 
occupied with the day by day problems of in- 
stallation, operation, and maintenance; conse- 
quently, the amount of activity devoted to 
modifications and changes in the equipment 
that operational experience had proved to be 
necessary was very limited. 

The RCM program in the Fifteenth Air 
Force, as the RCM program in all the other 
air forces organized during World War II, suf- 
fered because of the fact that RCM installations 
had to be handled in a way different from that 
in which signal equipment of a standard nature 
was dealt with. Because of supply difficulties, 
the number of electronic jamming sets available 
to the Fifteenth Air Force in the period be- 
tween January 1944 and October 1944 was 
insufficient to keep the necessary large-scale 
program going. This was indeed unfortunate 


because that period was a very important one 
in the history of the Air Forces. 

When RCM equipment became available, the 
problem of installation was a very serious one. 
Service Command personnel took care of the 
major part of the work. However, trained per- 
sonnel were not available in sufficient quantity 
in the theater, and personnel had to be trained. 
This training of installation teams, which in 
the early part of 1944 had been done by the 
RCM Sixteenth Reconnaissance Squadron, was 
in the fall and winter of 1944 handled by a 
Service Command Depot which became the 
center of all the RCM activities. Installations 
involving large quantities of equipment were 
made in the groups, but the Air Depot prepared 
all the necessary kits. In addition, civilian 
technical observers from the Radio Research 
Laboratory of Harvard took a leading role at 
this time in organizing the different parts of 
the program. Mobile vans were going from 
group to group to help in the installation and 
to give a series of lectures to all the personnel. 
Because of the necessity of getting in touch 
with all the personnel, the same lecture had to 
be repeated two or three times. Different lec- 
tures were given to staff officers, combat crews, 
and RCM and signal personnel. 

Chaff 

The very first use of Chaff in the 15th Air 
Force was made about February 1944. The 
quantity used, however, was small because of 
lack of supply. Not until March 1944 did a 
substantial quantity arrive. 

Use of Chaff in appreciable quantity began, 
therefore, at the beginning of April 1944. Chaff 
was received with enthusiasm by the crews and 
the personnel of the Fifteenth Air Force. The 
effectiveness of Chaff at the beginning was 
exceedingly good, and the crews reported flak 
hitting the Chaff trails and not the bomber 
formation. After the first use of Chaff in April 
1944, the Chaff supplies were never very large, 
but they never reached as low a point as the 
supplies of RCM electronic equipment. 

In the first months, the amount of Chaff 
dropped was of the order of 12 units a minute, 
substantially lower than the figure used later. 
Because of the limited amount of Chaff avail- 


THE OPERATIONAL USE OF RCM IN THE MTO 


283 


able, Chaff was not dispensed by all the forma- 
tions but only by those flying in the leading 
positions. 

It was clear that the amount of Chaff pro- 
tection given to the leading formation was 
rather small as compared to the amount of 
protection available to formations flying within 
or near the Chaff trail. It was, therefore, de- 
cided to attempt a type of operation in which 
Chaff was dispensed ahead of the leading for- 
mation by means of fighters. Since Chaff dis- 
pensers for fighters were not available at that 
time, special Chaff bombs were prepared. 
Fighters equipped with these Chaff bombs flew 
ahead of the main formation and dropped Chaff 
bombs at the proper intervals up wind of the 
main bombing run. The effective success of 
Chaff in all the operations made another revi- 
sion of the Chaff requirements for the Fifteenth 
Air Force necessary. The requirements were 
revised upwards to a figure of three million 
units a month, and an attempt was made to 
keep the figure of Chaff dispensed on the order 
of 27 units per minute per aircraft. Chaff was 
still used only on heavily defended targets until 
at least the end of September. Chaff bombs were 
reported very successful, with some crews see- 
ing very wild shooting by the enemy flak 
batteries, with bursts often several miles from 
the nearest formation. At the end of August 
1944, the Twelfth Air Force also began to use 
Chaff in B-25 and B-26 aircraft. During the 
months of October and November, Chaff was 
used by both the Twelfth and Fifteenth Air 
Forces in larger quantities, with more and more 
formations dropping Chaff. 

The need for Chaff dispensers was very 
keenly felt and the first prototype using the 
A1 Chaff dispenser developed in the United 
States was flown satisfactorily. It was found, 
however, that changes had to be made in order 
to make it suitable for installations in all the 
aircraft of the Air Forces. 

The arrival of a substantial number of A1 
Chaff dispensers in January 1945 enabled the 
Fifteenth Air Force to begin the installation of 
them in its operational bombers. However, 
serious difficulties were encountered because of 
mistakes made in the United States during the 
assembly of the stripper gear. The help of a 


specialist was requested from England and the 
work of installation was ^stopped for a while. 
In March 1945, the arrival of the specialist 
from England enabled the work on Chaff dis- 
pensers to be continued. Changes were made in 
the dispensers and mockups prepared for all 
types of aircraft involved. Three hundred dis- 
pensers were installed in six groups on the 
basis of 50 installations every three weeks. Not 
only the dispenser but also the chute had to 
be changed both in the B-25 and in the heavy 
bombers. In the month of April, the work on 
the installation of Chaff dispensers really was 
going at full speed. As of April 15, 1945, more 
than 500 dispensers had been installed. 



Figure 5. A-4 type Chaff dispenser intended for 

fighter installation in order that protection 
could be given to lead bomber formations. 


The RCM program of the Twelfth Air Force 
was limited because of tactical considerations. 
The B-25’s of the 57th Bomb Wing flew in such 
formations and principally at such altitudes 
that countermeasures could be considered effec- 
tive only under blind bombing conditions, and 
thus, until the installation of their Shoran 
equipment in the fall of 1944, there was little 
in the way of RCM requirements. Looking 
toward the installation of blind bombing equip- 
ment, however, plans were laid to combine an 
effective RCM program with the blind missions, 
and also to get what benefit could be obtained 
by direct action on visual missions. The “direct 
action’’ was taken by a small lead formation. 
This lead formation would approach the gun 
positions, attempting to cross the target on the 


284 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


axis of attack for the following bombers, laying 
a Chaff trail to cover the bombers. They would 
then bomb the gun positions with white phos- 
phorus bombs, with the dual aim of demoraliz- 
ing or injuring gun crews and also of obscuring 
the visual range finders. If it was not possible 
to continue over the target to the gun positions, 
the lead group would hold the bomber axis as 
long as possible and then break into their own 
run. On visual missions, the white phosphorus 
was considered the primary countermeasure 
and Chaff secondary. On obscured missions, the 
Chaff was the primary countermeasure and the 
phosphorus secondary. 

Ultimately, it was planned to install spot 
jammers in about 10 per cent of the aircraft, 
and Chaff dispensers in a larger percentage, 
but operations ceased before any jammer 
activity was initiated and only a small number 
of dispensers had been installed and used. 

14.6.3 Fighter Countermeasures 

For reasons already mentioned, the amount 
of RCM directed against fighters was very 
limited and sporadic. The British bombers 
based in the Mediterranean and conducting 
night bombing activities did use a certain 
amount of radar countermeasures against the 
enemy EW system. These countermeasures 
were carried on by the use of British Mandrels 
employed against German Freyas. A small 
number of other sets peculiar to the RAF were 
used by these Wellingtons, but no large-scale 
effort ever took place. 

In the late part of 1943, a plan was started 
within the headquarters of MAAF to establish 
a ground jammer station in Corsica. At that 
time, the Germans occupied the whole coastline 
from a point north of Naples all the way to the 
Spanish border. Corsica being in the middle 
of the western part of the Mediterranean was 
in a reasonably good position to conduct ground 
jamming. For this reason, the authorities in 
the United States were requested to prepare 
and send to the theater a Signal Corps unit 
known by the code name Beaver III. When the 
unit was requested, no definite operational plan 
existed for its use. Because of its position, with 
reference to the enemy radar chain, no complete 


jamming coverage of the approaches to the 
enemy coastline could be guaranteed except 
within a distance of about 40 or 50 miles. 
Furthermore, jamming facilities available to 
the unit were such as to cover only the Freya 
frequency band. Observations of the signals 
from enemy coast-watcher stations appeared 
to show that these stations were also used as 
early warning. These reasons, coupled with the 
fear that jamming operations against the 
Freya chain might have interfered with the 
Allied v-h-f communication network, prevented 
the Beaver III unit from carrying on any 
continuous jamming work in support of the 
strategic air forces. After several delays due 
to the uncertainties in the organizational and 
operational planning setup, the unit arrived in 
Corsica during the month of March 1944 and 
completed the installation of its equipment dur- 
ing the first days of April. Before that time, 
a series of tests had been conducted at Oran 
to determine the limitations of jamming equip- 
ment imposed by the danger of communications 
interference to friendly sets. 

After the unit was installed, it used its re- 
ceiving and DF facilities to obtain information 
on the enemy radar chain, but did not conduct 
offensive countermeasures until D-Day in sup- 
port of the invasion of southern France. Men- 
tion has already been made of the value of the 
search information obtained by Beaver III. It 
must be mentioned here that the invasion of 
southern France occurred at a point on the 
coastline very far (about 120 miles) from the 
island of Corsica and that therefore the jam- 
ming of the enemy radar chain was a difficult 
task. The details of the RCM plan for the inva- 
sion of southern France will be given in a later 
section, where mention will be made of the part 
that Beaver HI played in the operation. 

It might be useful to note here that the 
Beaver unit had attempted three times during 
World War II to do an effective job of ground 
jamming. The first time the unit was deployed 
against the Japanese radar in Kiska, the sec- 
ond time in Corsica, as previously discussed 
here, the third time in the Pacific Theater. In 
none of these three cases was any effective con- 
tinuous ground jamming found to be possible, 
because of strategic or tactical considerations. 


THE OPERATIONAL USE OF RCM IN THE MTO 


285 


Miscellaneous 

Among the miscellaneous activities carried on 
in support of the RCM program were the test- 
ing activities first conducted by the Sixteenth 
Reconnaissance Squadron and by the Fifteenth 
Air Force. 

When Italy fell, one captured enemy GL set 
out of three available was left in the theater. 
The other two were sent to England and the 
United States for intelligence purposes. This 
set, after some work, was put into working 
order and was used in two series of tests carried 
on in 1944. The first test, during the month of 
March, had the purpose of testing the effective- 
ness of our electronic jamming. The results 
were quite interesting but the test was handi- 
capped by the difficulty of obtaining a sub- 
stantial number of planes to simulate a forma- 
tion. Later in the year, the Fifteenth Air Force 
supplied the necessary number of aircraft and 
a series of flights was flown against the cap- 
tured set in order to test the effectiveness of 
the Chaff-dispensing technique. For several 
reasons, the quantitative results were not com- 
pletely satisfactory, although they were very 
useful to the people in charge of the planning 
of the RCM operation. The number of Chaff 
units necessary to cover a formation was de- 
termined from these tests, and this figure was 
used until more complete results became avail- 
able from work done in the United States. 

Another activity worth mentioning is one in- 
volving work to protect friendly radar sets 
against the jamming carried on by the enemy. 
During the months of April, May, and June 
1944, a substantial effort was carried on by the 
Germans in the jamming of Allied ground sets 
in the Anzio beachhead and airborne aircraft- 
interception sets. It was very unfortunate that 
the lack of appreciable diversification of the 
frequencies of the Allied EW, GCI, and AI sets 
increased their jamming vulnerability. A large 
percentage of these sets were working at fre- 
quencies around 200 me, so that the Germans 
with a few ground-based jamming transmitters 
tuned around that frequency managed to inter- 
fere very seriously with our operations. The 
jamming carried on by the Germans consisted 
essentially of C-W and railing jamming. Win- 


dow was also used very extensively. It is impor- 
tant to note that jamming was so effective as to 
make our 200-mc GL equipment practically 
worthless and to make the work of our AI set 
very much more difficult than it had been in 
the past. As a consequence, there was a large 
decrease in the number of enemy aircraft shot 
down by night fighters. The GL radar position 
in the Anzio beachhead was greatly improved 
when more modern sets like the SCR-545 and 
SCR-584 were brought into the beachhead. A 
further improvement was obtained when the 
more modern microwave AI set was substi- 
tuted for the older 200-mc Mark IV AI set used 
up to that time. 

Before these sets became available, however, 
work had been requested by the radar personnel 
on the development of antijamming devices. 
These AJ devices were developed and installed 
by one of the civilian technical observers. Modi- 
fications were made in the radar set, the fre- 
quency band of the i-f stages was decreased, 
and noise limiters were installed. One of the 
reasons why all the GCI sets were working 
around the frequency of 200 me was that no 
large spread of frequency was possible with the 
type of IFF using the G band. An effort was 
made to modify the IFF to allow for a spread 
of about 10 me. These efforts were successful, 
but no large-scale work was done because the 
new sets became available about that time. 


14.6.5 jYie Effectiveness of the RCM 
Program 

After the defeat of Rumania by the Russian 
troops, a technical mission was sent to Rumania 
about August 1944 to analyze the flak defenses 
of the Rumanian targets which had been hit 
by the Fifteenth Air Force. The results obtained 
by these investigation teams were of the high- 
est interest. Up to that time, the amount of 
Chaff used by the Fifteenth Air Force had not 
been very large but had been reasonably satis- 
factory; the amount of electronic RCM used, 
however, had been extremely limited. Despite 
this fact, the reports that the intelligence offi- 
cers brought back were of such a nature as to 
give the impression that RCM had been effective 


286 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


beyond the most optimistic hopes. The Ru- 
manian officers interrogated gave tremendous 
credit to RCM in decreasing the amount of flak 
losses suffered by the Fifteenth Air Force. They 
said, for instance, that RCM was not only useful 
in days when the overcast prevented the optical 
range finders from operating, but also on the 
days in which the visibility was good, because 
the smoke screens used by the defenders made 
the use of radar very important. They added 
that RCM had put these radars out of action 
many times. In listing their suggestions for the 
improvement of the American raids for the 
purpose of decreasing their flak risk, RCM had 
first priority. A measure of the effectiveness of 
the enemy flak, or, better, a measure of its in- 
effectiveness, can be given by the figures of the 
number of shells shot by all the batteries of 
Ploesti, the second most heavily defended tar- 
get in the world. The number of planes shot 
down and the ammunition expended was such 
that about 25,000 rounds were found to be 
necessary to shoot down one plane. These fig- 
ures should be compared with the figure of 
about 350 rounds per bird used by the American 
and British ack-ack batteries to shoot down 
buzz bombs. 

After V-E Day, a mission was sent to north- 
ern Italy for the purpose of studying the flak 
situation there and, if possible, to evaluate the 
success of our countermeasures against their 
radar gun-laying system (see Figure 6). The 
following abstract from the report written on 
the subject gives a summary of the results ob- 
tained. 

It was perfectly clear that, at least in the Italian 
Theater, German officers in staff positions had very little 
respect for their gun-laying radar. The reason for this 
was twofold. 

1. The educational program was limited because of 
the secrecy restrictions. 

2. The interference by Allied countermeasures seri- 
ously affected the radars’ operation. 

An example of the poor educational program is the 
fact that several flak battery commanders believed that 
their radar had attracted Allied bombers and bombs, 
and had sometimes ordered it turned off. 

An accurate opinion on the effect of Allied counter- 
measures could only 'be obtained from the junior offi- 
cers in charge of equipment. However, in spite of the 
limited knowledge possessed by each officer, every one 
of them voluntarily mentioned the effect of RCM, and 
knew the names and use of several of their anti- 


jamming devices. Of course their opinions varied on 
the effectiveness of the interference, and in general, 
varied with the rank of the officer. A flak battalion 
commander would generally say that Allied interference 
was often encountered, but that their anti-jamming 
devices, which he would describe, were usually able to 
counteract any form of interference. And in cases where 
radar was jammed, — it didn’t really matter because they 
always depended on the optical system. 

The junior officers directly responsible for the opera- 
tion of the batteries had a somewhat different view. 
These officers believed that the small Wurzburg could 
be more accurate than the optical system, if it were 
not interfered with by jamming. However, the Allied 
countermeasures had made this gun-laying radar of 
little use against four-engine bombers. The continuous 
interference from Chaff and electronic jamming had not 
given the radar a chance. Opinions were divided on the 
most effective form, but generally favored the Chaff 
operation. In most cases, they seemed to be able to side- 
step the electronic jamming, but often it was only 
temporary. Ff-equently it was possible to eliminate the 
Chaff interference, but occasionally the concentration 
was so high that Wurzlaus had little effect. 

One of the most startling impressions came from the 
young German officers who felt that the high command 
in general was too conservative and backward. One 
lieutenant, a young physicist who knew of the world’s 
great scientists and their work said, “The war turned 
with our defeat at Stalingrad and the use of Rotterdam 
(British H2S).” 

Frank opinions of the junior officers were never given 
in the presence of their seniors. However, one major. 



Figure 6. Radio Research Laboratory technical 
observers and Fifteenth Army Air Force officers 
interrogating German radar and flak officers in 
Italy. 

a battalion commander, was amazed that the Allied 
scientists were so young, and remarked, “We were 
fighting against children, — and we were beaten.” 

The Allied use of RCM, its effects, and the German 





THE OPERATIONAL USE OF ROM IN THE ETO 


287 


anti-jamming devices was one subject of which all 
channels of command were well aware. The repeated 
failure of their gun-laying radar under Allied RCM, 
and a lack of education produced rumors on the equip- 
ment and had caused it to be considered, even at the 
batteries, as a secondary means of flak control. 

During the last six or eight months, the intensity of 
the Allied jamming had increased until both radar 
operators and technical personnel believed “the game 
was about up.” Chaff concentrations were reported to 
have placed the noise level too high for Wurzlaus 
operation, and the use of Carpet had forced the fre- 
quency of the Wurzburgs to the practical limits. The 
general opinion was that Chaff generally had more 
effect than Carpet. They definitely agreed that the use 
of both forms of interference was still advantageous on 
a clear day. 


7 THE OPERATIONAL USE OF RCM 
IN THE ETO 

^ Search and Investigation 

The RCM program of the U. S. Armed Forces 
in the ETO began in the summer of 1942 when 
the Eighth Air Force began to be interested in 
the problem of enemy radar. Because of the lack 
of more suitable search equipment, an investi- 
gation of the use of radar by the enemy during 
Eighth Air Force attacks was commenced with 
a British warning receiver called Boozer, which 
was installed in a heavy bomber of the attack- 
ing formation in order to determine where the 
radar signals could be heard during the attack. 
The results of this search immediately indi- 
cated that, as expected, enemy radar was being 
used during these daylight attacks. Thus still 
further interest was aroused in using Carpet 
to jam the enemy radar. 

The Carpet program was started by the 
Eighth Air Force on October 8, 1943. The initial 
information on the Wurzburg frequency band 
was obtained from the British, and on the first 
mission Carpets were tuned at intervals of 1 me 
over the frequency band of 550 to 570 me. Inas- 
much as the Carpet program was based on 
jamming the frequency band where the enemy 
operated, an obvious antijamming measure by 
the enemy was to spread his radar frequencies ; 
the wider the frequency spread, the more dif- 
ficult it would be to cover it adequately, par- 
ticularly with a small number of equipments. In 


order to keep track of the spread of the enemy’s 
frequencies, it was necessary to maintain 
throughout World War II a continuous investi- 
gational program with airborne search re- 
ceivers. 

In October 1943, ABL-15 provided the Eighth 
Air Force with a few handmade models of a 
Blinker search receiver, a receiver which re- 
quired an operator and which had a panoramic 
type presentation. To determine the enemy fre- 
quency, the receiver was first used to search 
in the German Wurzburg band from 450 to 650 
me. A Blinker search receiver was first flown 
on November 15th, and after this time search 
receivers were flown on almost all missions con- 
ducted by the Eighth Air Force. The first re- 
sults from the use of this equipment showed 
that the enemy frequency band had spread to 
possibly 524 to 597 me. It was difficult to make 
an accurate statistical study of the frequency 
distribution of flak radar by means of this 
equipment, since no means other than aural 
was provided to differentiate between the large 
and small Wurzburgs which were believed to be 
used for GCI and flak control respectively. 

Search operations were continually extended 
after these initial operations and were a very 
important part of the RCM program. As im- 
proved equipment became available, more and 
better information was obtained concerning the 
enemy’s operation. The Carpet and Chaff pro- 
grams were continually modified as a result of 
these search operations. 

A British recording receiver known as Bagful 
was first tested operationally in January 1944 
by the Eighth Air Force. The distribution of 
frequencies used by enemy radar equipments 
was thus recorded and careful analysis was 
made of the results. Unfortunately, Bagful did 
not distinguish between the small and large 
Wurzburgs, which had different pulse-repeti- 
tion frequencies [prf ] , and, therefore, complete 
reliance could not be put on this equipment for 
recording the frequency spread. 

In January 1944, the use of the Blinker re- 
ceiver was extended to the 250 to 450-mc band 
in an attempt to determine whether dangerous 
enemy radar signals existed in that region. 
Some work was carried out by ABL-15 on the 
design of a prf meter for the Blinker receivers. 


288 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


although this work was not too successful since 
the equipment failed to operate properly when 
more than one radar was on the same frequency 
at the same time, which often was the case. 

Since the flak losses of the Ninth Air Force 
were very low compared with those of the 
Eighth, considerably less priority existed on 
RCM in that command, but in the early part of 
1944 a Blinker search receiver was installed in 
a B-26 aircraft and a search program carried 
on for several months in an attempt to deter- 
mine whether the RCM problems of this com- 
mand were similar to those of the Eighth. 

The Eighth Air Force commenced flying 
radar screens in the beginning of 1944. The 
purpose of the screens was to prevent the enemy 
EW radar from detecting the approach of 
bomber formations for as long as possible. In 
connection with these screening missions, a 
number of search programs were conducted in 
order to determine how the enemy EW radar 
was used during these attacks. The German EW 
radar system became very complex before the 
end of World War H, and much of the informa- 
tion concerning the subject was obtained by 
the British through their ground listening sta- 
tions and airborne intercepts. 

The Eighth Air Force commenced flying 
AN/APA-17 radar DF equipment in July 1944. 
It was hoped that this equipment would aid in 
the problem of locating and identifying speciflc 
ground radar installations, and that by a study 
of the operational procedures of a given station, 
considerable information of value to the RCM 
program could be obtained. Because of the high 
density of German radar, it was very difficult 
for an operator to follow a single radar station 
for a long period of time. Direction-finding fixes 
which supposedly were made on one station 
were often found to have been taken on several 
ground radars. An interesting use of the 
APA-17 equipment developed during these op- 
erations. Operators found that by noting the 
direction of large concentrations of radar sta- 
tions, it appeared to be possible to predict the 
location of flak areas, and on several occasions 
when the formations became lost over enemy 
territory, it appeared feasible to use the equip- 
ment as an aid to avoiding regions of heavy 
flak. 


An ever-present cause for fear in the Air 
Forces RCM program was that the enemy would 
resort to entirely new radar equipments for flak 
control. One of the obvious steps in this direc- 
tion would have been the use of microwaves, 
and it was considered important for this reason 
to maintain a search program for new enemy 
signals outside of the usual range. In June 1944, 
an APR-5 microwave search receiver was in- 
stalled in an Eighth Air Force B-17, and it was 
occasionally flown over enemy territory after 
this time. In February 1945, the APR-7 micro- 
wave search receiver was installed and flown 
by the Eighth Air Force in a P-38 aircraft, and 
later in the main bomber force, in order to 
search for the use of microwave radar by the 
enemy. The results of these microwave searches 
were not significant and although a number of 
signals which did not appear to come from Allied 
equipment were recorded, positive identifica- 
tion was difficult to make. 

Toward the end of World War II, the APA-17 
direction-finding equipment was fitted with a 
microwave head for use in connection with this 
search. Because of the many unidentified 10-cm 
intercepts which had been made, it was essential 
that means be provided, such as by DF equip- 
ment, for positive identification of the signal as 
enemy or friendly. An operator training setup 
was constructed in connection with the pro- 
gram, but the progress of the war was such that 
it did not come into use. 

Because of the scarcity of production re- 
ceivers for the spot- jamming program, investi- 
gations were started to try to find alternative 
equipment for the purpose. In addition to the 
use made of the small number of Blinker equip- 
ments mentioned previously, a few APR-1 re- 
ceivers were obtained from the U. S. Navy and 
used. It was found that the British Carpet II, 
with suitable modifications, could be employed 
as a receiver, and a number were so used by the 
Eighth Air Force. 

The search for a suitable and available re- 
ceiver for spot jamming and the improbability 
of obtaining such receivers in the near future 
from the United States led to the design by 
ABL of a simple autodyne receiver. Approxi- 
mately 500 of these receivers were constructed 
at the Air Force Base Air Depot from the 


THE OPERATIONAL USE OF RCM IN THE ETO 


289 


laboratory design. Personnel of the laboratory 
aided with the testing and supervision of this 
program and eventually with the installation 
problems. The equipment proved to be useful 
and many sets saw actual operational service. 
However, since the equipment was inferior in 
operation to the APR-4 receiver, it was replaced 
when APR-4’s became available in the fall and 
winter of 1944. 

The arrival of APR-4 search receivers in small 
quantities in September 1944 permitted their 
use in the search aircraft of the Eighth Air 
Force, replacing Blinker receivers. ABL-15 built 
a number of audio oscillators for use with these 
receivers because of the shortage of much 
equipment in the theater. The audio oscillators 
were used with the APR-4 and whatever oscillo- 
scopes could be obtained for measuring the 
characteristics of enemy signals. These oscilla- 
tors were designed around the American SCR- 
274N command receiver, using some of the com- 
ponents, and a number of these oscillators were 
made at the Base Air Depot from the ABL-15 
design. 

In the beginning of 1944, the Eighth Air 
Force commenced a program of enemy v-h-f 
intercepts which carried through until the end 
of World War II and undoubtedly was of con- 
siderable value in obtaining much needed in- 
formation from the enemy ground and airborne 
fighter traffic. S-27 and later German Fuge 16 
receivers and German-speaking operators were 
carried in the bomber formation. Some attempts 
were made to use magnetic and disk-type re- 
corders in this program, but these were not 
thought to be particularly useful. The results of 
all of these investigations were immediately 
transmitted to the British Intelligence Organ- 
ization and from them directly to the Eighth 
Air Force, which made use of them in opera- 
tional planning. 


Flak Countermeasures 

Carpet 

The first shipments of Carpets arrived in the 
theater in September 1943 and were installed 
in two bomb groups of the Eighth Air Force. 
These jammers were first used on October 8, 


1943, by 38 of the 42 aircraft of the 388th and 
96th Groups in an attack on Bremen. Initial 
reports indicated considerable success in the 
reduction of flak losses and as a result the Car- 
pet program received great impetus. From the 
commencement of the program at this time up 
to October 1944, when adequate deliveries of 
equipment made extensive use of Carpet pos- 



Figure 7. ETO spot-jamming installation in a 
B-24. Shown from top to bottom are 1 
AN/APT-2, 1 AN/APR-4, 1 AN/APQ-9, and to 
the left, 1 AN/APT-2. 

sible, only about 9 per cent of the Air Forces was 
equipped with Carpets. Sufficient additional 
equipments were received after the initial quan- 
tities to keep up with the increase in the size 
of the Air Forces and to replace losses, so this 
percentage was maintained for about a year. 
The Eighth Air Force Carpet program from 
October 1943 through April 1945 is given in 
Table 2. 

With the instigation of even so small a Carpet 
program in the last months of 1943, the Ger- 
mans attempted to counter the use of electronic 
jammers by spreading their flak radar frequen- 



290 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


cies. With only a very few Carpets available, 
it was important that equipment be used to 
maximum advantage. For this reason, consider- 
ation was given to modifying Carpet so that an 
operator could tune it rapidly, by means of a 
monitoring receiver, to the enemy radar fre- 
quency. By this means, if 100 per cent effective 
operation were possible, the number of jammers 
required would be equal to the maximum num- 
ber of enemy radar stations in use against the 
formation at any one time, which would be 
only a fraction of the number of barrage jam- 
mers needed. ABL-15 commenced work in De- 
cember 1943 on the use of Carpet as a manu- 
ally tuned spot jammer for both the 8th and 
9th Air Forces. A standard Carpet I trans- 


Table 2. Eighth Air Force Carpet program. 



Number groups 

Total number sets 



equipped 

installed 

Comments 

Date 

Barrage Spot 

Barrage 

Spot 


1943 

Oct 4 

1944 

2 

0 

68 



Feb 16 



125 



March 



177 


101 Sets lost since 






start of program. 

April 1 

4 


124 



May I 

4 


148 



May 15 

6 


223 



May 21 

6 

1 


6 

Spot jamming started. 

June 15 

6 


215 

6 


July 15 

6 


165 

31 


Aug 1 

6 

4 

184 

65 


Sept 10 

6 

4 

141 

62 


Oct 10 

6 

4 

120 

81 


Nov. 1 

10 

11 

1,342 

126 


Nov 20 

28 

13 

2,746 

147 

Dual Carpet barrage 






in all aircraft ex- 
cept Pathfinder 
practically com- 
pleted. 

Dec 10 

38 


3,098 

253 

Spot-jamming instal- 






lations starting in 
all divisions on basis 
of 12 aircraft 
equipped per group. 

Dec 31 
1945 

40 


3,460 

507 


Feb 1 

40 



1,254 

Spot installations es- 






sentially complete. 

April 1 

40 

40 

2,608 

1,260 

Triple barrage instal- 






lations commencing. 


mitter was modified so as to make it possible 
to tune the equipment rapidly over a band 75 to 
100 me wide at any frequency in its range of 
450 to 710 me. This equipment was first flown 
in May 1944 by the 44th Group of the Second 
Division, 8th Air Force, and, although this 
program was extended to three other groups in 
August, it was not until the winter of 1944-1945 
that the spot- jamming program was complete. 


Eventually this equipment was used in about 
two planes per squadron of 12 aircraft, with one 
operator and three jammers per spot jammer- 
equipped aircraft. 

In January 1944, both the 8th and 9th 
Air Forces requested the laboratory to test the 
British automatic-selective jammer Carpet II, 
with a view toward using it in their bomber 
formations. The British Carpet II was an equip- 
ment which automatically hunted for the fre- 
quency of the enemy radar station, then locked 
on it, and jammed for a predetermined length 
of time, functioning, in effect, as an automatic 
spot jammer without an operator. However, 
since the power output of this jammer was only 
about 1/2 w, it was determined that the number 
of equipments which would be required ade- 
quately to jam the German small Wurzburgs 
would be excessive. 

The training of operators was an important 
part of the spot- jamming program, and in June 
1944 the Eighth Air Force assigned certain 
aircraft of the 36th Squadron to be equipped 
with training installations of spot- jamming 
equipment; in addition, bench spot- jamming 
setups equipped with signal generators simulat- 
ing a small Wurzburg aided in the training pro- 
gram. This training program reached consider- 
able magnitude when the installation of spot- 
jamming equipment in all the groups of the 
Eighth Air Force was commenced in November 
1944. 

As is indicated in Table 2, the Carpet pro- 
gram was very small during the period when it 
was needed very badly. However, the Carpet 
program reached full proportions for 6 months 
of the 8th Air Force’s 31 months of operations, 
and these 6 months were the months when the 
attacks on German targets were the heaviest. 
The following considerations, which were de- 
termined at the time when the Carpet program 
was reaching practically full strength, resulted 
in a decision to establish the RCM program of 
the Eighth Air Force on a basis of barrage and 
spot jamming, each supplementing the other as 
effectively as possible. 

1. The number of radars with which the 
enemy batteries were equipped was about one 
radar to each ten guns. On the heavily defended 
targets as many as 250 to 300 guns could en- 


THE OPERATIONAL USE OF ROM IN THE ETO 


291 


gage a formation and up to 15 radars could be 
tracking at the same time. 

2. By means of an investigational program, 
the density of enemy sets at all frequencies was 
determined. Barrage jamming was used to cover 
the region where the density was highest. In 
a 12-aircraft squadron with Carpets spaced 
1% to 2 me (this applies to APQ-9), a maximum 
of 48 me could be covered. This was definitely 
not enough to jam the whole enemy band; fur- 
thermore, for several reasons RCM sets had to 
be taken out of H2X aircraft, with a consequent 
reduction in the number of megacycles covered. 

3. Another element to be taken into account 
was the general trend toward the reduction to 
nine or ten aircraft per squadron; by the end 
of World War II, practically all divisions were 
flying eight RCM aircraft per squadron. 

The use of spot jammers alone would have 
been difficult since, as stated above, the number 
of radars looking at the formation at a given 
time might reach as many as 15. This would 
have required five or more spot- jamming air- 
craft per squadron, which would have presented 
serious problems in obtaining operators and re- 
ceivers. Furthermore, in the region where bar- 
rage was used it was probably more effective 
since, when the barrage jammers were care- 
fully tuned to their assigned frequency, a small 
rapid frequency shift on the part of the enemy 
radar would not result, as it might in the case 
of spot jamming, in the avoidance of the jam- 
ming for a short period. Actually, the ideal 
jamming system was a barrage; however, the 
impossibility of covering all of the enemy fre- 
quencies with barrage jamming eventually led 
to the adoption of spot and barrage jamming 
together. 

In conclusion, after several discussions in 
which all of the above factors were examined, 
a decision was reached to have two aircraft in 
each squadron carry three spot- jammer trans- 
mitters, and to equip all the other non-PFF 
(Pathfinder) aircraft with dual barrage instal- 
lations. 

The band covered by the barrage varied from 
time to time depending upon the results ob- 
tained by investigation of the enemy frequency 
distribution. For quite a few months starting 
in October 1944, each group of the Air Forces 


had two squadrons barraging the high band 
from about 550 to 580 me and one squadron 
barraging the so-called low band from about 
520 to 550 me. This distribution was changed 
when the enemy transferred a large proportion 
of its sets towards lower frequencies around 460 
me and was further changed when simple con- 
siderations showed it was better to have all the 
squadrons of a group covering the same band. 
A situation was reached at the end in which 
each squadron of a group jammed the same 
band but different groups barraged different 
bands; the spot- jamming operators were 
charged with the task of jamming all signals 
which appeared outside of the frequency bands 
being barraged. 

With the availability of sufficient Carpet IIPs, 
a program was started in November 1944, by 
the 8th Air Force, to replace all Carpet I’s 
with Carpet IIPs. An acute shortage of tubes 
for this transmitter developed as a result of 



Figure 8. B-17 crew member dispensing an 

early form of Chaff from chute in the radio 
room. 


their short life and the difficulty of obtaining 
spares, and ABL-15 conducted a thorough in- 
vestigation into the causes of the tube failures. 

Although large numbers of APT-5’s were 
never received in the theater, a small number, 
built on a crash program, were put into use in 
the 8th Air Force as spot jammers. Plans were 
made to replace, eventually, all Carpet I and III 
barrage and spot jammers with APT-5’s, but 



292 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


World War H ended just as large shipments 
were arriving. 

Chaff 

The Eighth Air Force first used Chaff on De- 
cember 20, 1943, about 2 months after Carpet 
was used for the first time. After V-E Day, it 
was found that the Germans had considered the 


were based on its use only by lead formations 
and not by all aircraft, as was later done. In 
Table 3 are given the quantities and types of 
Window which were used by the Eighth Air 
Force. 

Even in the summer of 1944 when practically 
all aircraft started dropping Chaff, the tactics 
remained stereotyped and it became standard 




Figure 9. A captured German photograph showing the appearance of a heavily infested Window area 
as contrasted with normal appearance of the A scope on a Wurzburg radar. 


use of a similar system in the summer of 1940, 
long before the first use by the Allies in 1943, 
but had kept it secret for security reasons from 
everyone except the high-level personnel. The 
success of Chaff was, therefore, very great be- 
cause of the element of surprise. 

When the American Air Forces began to use 
it, the supply was not sufficient for large-scale 
operations and British supplies had to be em- 
ployed for a considerable period. Perhaps be- 
cause of an erroneous concept of the accuracy 
of the navigation of the bomber formations, 
the requirements transmitted to the United 
States were far below the actual quantity 
necessary for a complete and effective program. 
In effect. Chaff plans and Chaff requirements 


practice to begin a few miles after the initial 
point [IP] and stop when leaving the target 
area. Fortunately, however, with universal use 
of Chaff, operating personnel gradually became 
accustomed to thinking of Chaff as another tac- 
tic available to them. Army and civilian techni- 
cal personnel contributed greatly to the under- 
standing of Chaff in the headquarters and 
operational units. As a result of the increasing 
familiarity of Chaff as a weapon, the methods 
of employing Chaff increased in variety and in 
number beyond the standard dropping tech- 
nique already outlined (which involves dropping 
about 24 units a minute from each aircraft in 
the target area). Mosquito aircraft were 
equipped with Chaff dispensers and were flown 




THE OPERATIONAL USE OF RCM IN THE ETO 


293 


ahead of the main formation to dispense Chaff 
before the bombers arrived. Special bomber 
forces were equipped with chutes to permit the 
dispensing of large quantities of Window in a 
short time and were sent ahead of the main 
formation. Fighters were equipped with Win- 
dow-filled droppable flare bombs and often Chaff 
tactics were employed only with the general 
purpose of confusing the enemy with new and 
unexpected effects. Chaff forces were called 
upon one day to circle a target, dispensing 
Chaff, or to lay a Chaff trail along a course per- 
pendicular to the penetration course of the main 
force. In other cases, a division bombing Target 
A would dispense Chaff up wind of Target B, 
which another division was going to bomb 10 
min later. These and many other examples could 
be given of the variety of employments of Chaff. 


Table 3. Use of Window by Eighth Air Force. 


Date 

Used per month 

Types 

1943 

Dec 20 

First use 

CHA3 

1944 

Feb 

Approximately 80,000 lb 

CHA3, and British A, C, 
and G 

Mar 

250,000 lb 

CHA3, A, C, G, J 

Apr 

519,000 lb 


May 

713,000 lb 


June 

1,145,000 lb 


July 

1,601,000 lb 

CHA3, C, F, G, J, X 

Aug 


CHA2, 3, 28, C, F, J, J3 

Sept 

5.6 million units* 

CHA3, 28, F, J, X 

Oct 

7.2 million units 

CHA3, 2, 28, 28-3, J, J3, X 

Nov 

6.4 million units 


Dec 

6.3 million units 

CHA28-3, 3, F-3, J, J3, X 

1945 

Jan 

5.3 million units 


Feb 

8.5 million units 

CHA28-3, F-3, A, X, XE 

Mar 

10.8 million units 

CHA28-3, F-3, A, X, XE 

Apr 

5.9 million units 

CHA28-3, F-3, A, X, XE 


* Exact conversion to weight cannot be made because of the many 
different types of British and American Window which were used. 


The time came at the end of 1944 when all 
the operational personnel were cognizant enough 
of the capabilities of the little strips of alu- 
minum made available to them that the Head- 
quarters Eighth Air Force decided it was ad- 
visable to leave to the subordinate division 
headquarters complete freedom of action in the 
use of this countermeasure. The amount of 
Chaff required increased continuously and, when 
tests against a Wurzburg equipped with a cap- 
tured AJ device showed that it was desirable to 
double the amount of Chaff dropped, require- 
ments were initiated for as many as 20,000,000 
units — more than 2,000 tons — of Chaff a month. 


Inasmuch as World War II ended, however, no 
deliveries of the increased quantities were actu- 
ally made, but this example is given for the 
purpose of contrasting it with the initial re- 
quirement made in December 1943 of 500,000 
units a month. 

Chaff dispensers were considered at several 
times as a standard item for all bombers, but 
it was repeatedly found that the manual dis- 
pensing method used until the end of World 
War II was satisfactory. However, the United 
States authorities had been requested to install 
Chaff dispensers in all replacement aircraft. 
Again, the end of the war prevented this re- 
quest from being fulfilled. 

With the definite possibility of use by the 
enemy of centimeter equipment and in the ab- 
sence of an electronic jammer covering the 
centimetric band, a requirement was established 
in early 1945 for 1,000,000 units a month of 
centimeter Chaff to be kept stored as insurance 
against future enemy developments. Fortu- 
nately, World War II ended before the Germans 
were able to make use of centimeter radar on 
a large scale and, therefore, the centimeter 
Chaff was not used. 


14.7.3 Fighter Countermeasures 

Countermeasures against German fighters did 
not play nearly so large a part in the electronic 
warfare of World War II as flak countermeas- 
ures. Table 1 indicates that the maximum losses 
of all bombers to enemy fighters occurred in 
the period January to July 1944. However, at 
this time, losses to flak had climbed very con- 
siderably over the previous six-month period 
and, therefore, there was not so much emphasis 
on fighter RCM during that period as there was 
in the previous year when the fighter losses 
were many times the flak losses. Also, as men- 
tioned previously, with the advent of the long- 
range fighter and a full-fledged offensive against 
the Luftwaffe, the whole strategy became one 
of welcoming combat in order to weaken the 
enemy. It will, therefore, be seen that the ad- 
vent of the long-range fighter greatly changed 
the need for a countermeasures program. In 
1942 and 1943 a vigorous fighter countermeas- 


294 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


ures program would probably have been very 
successful. However, at that time American 
knowledge of RCM was meager and equipment 
to do the job was lacking. 

A project was undertaken in December 1943 
to jam the German fighter communications in 
the frequency range 38 to 42 me with ground- 
based jammers located on the eastern coast of 
England. Prior to this time, the RAF had under- 
taken a similar program and had installed 600-w 
f-m barrage jammers known as Ground Cigars 
for this purpose. 

Since a single installation would have been 
satisfactory for both the RAF and the Eighth 
Air Force, steps were taken to insure British 
and American cooperation in this project. 
Studies made by ABL-15 of the existing British 
setup indicated that these installations were 
not very effective in jamming the enemy be- 
cause of insufficient power. The modification of 
these barrage jammers was undertaken to make 
them suitable for spot jamming, so that they 
could be quickly tuned over the desired band 
and monitored onto the enemy signal by an 
operator. In addition, a very substantial im- 
provement over the existing Ground Cigar an- 
tenna installation was made by erecting the 
antenna on the top of a 360-ft chain-home [CH] 
radar tower. Plans were made for the modifica- 
tion of 15 of these jammers, but the interest 
of the Eighth Air Force in the project decreased 
as the fighter problem was solved by the use 
of Allied long-range fighters and the program 
was never carried through. 

In December 1943, the 8th Air Force com- 
menced the installation of equipment to operate 
as an airborne radar screen to jam the German 
EW system. The screen was flown early in 1944 
for a number of months, although the useful- 
ness of this effort was rather doubtful. The air- 
craft carried Carpet transmitters to jam the 
Wurzburgs and Mandrels to cover the Hoardings 
and Freyas. Ordinarily the screen was used 
during bomber assembly periods and was placed 
parallel to the enemy coast at about 70 miles 
distance. There were several reasons why the 
screen may not have been successful, one of 
which was the difficulty in preventing the bomb- 
ers from using radio during the course of the 
assembly. 


Among the jammers available to cover the 
frequency bands of the enemy EW stations. 
Mandrels and direct-noise amplifiers (Dinas) 
were the most important. Rugs and Carpets 
were also considered. Essentially, the problem 
of jamming the whole EW network involved 
work on the frequency band from 70 to 220 me, 
and the somewhat less important bands from 
350 to 380 me and from 520 to 590 me. A fre- 
quency of about 36 me was added to this, later 
in World War H, because there were one or two 
enemy stations of that frequency on the Dutch 
coast. The type of station against which jam- 
ming was necessary covered the whole range 
from the old-type Freya with relatively low 
gain and low power to the big Hoarding and 
the Jagdschloss. When considerations of beam- 
width are taken into account, it is easy to 
realize how difficult was the problem of screen- 
ing a formation, especially at short distances 
from the enemy chain of radar stations. Any 
solution of this problem involved about seven to 
ten aircraft spread over a 100-mile front, each 
aircraft carrying from 10 to 20 jammers and a 
corresponding number of antennas. These fig- 
ures are quoted to give an idea of the order of 
magnitude of the effort involved, and effective 
screening was not expected after the formation 
was within 50 miles of the enemy radar sta- 
tions. 

The screen project was revived again in De- 
cember 1944, partially because of the possi- 
bility of serious trouble from the enemy jet 
aircraft. A thorough study of the problem was 
made by the Operational Analysis Section, 
Eighth Air Force, and by ABL-15. At the time, 
it was expected that the screen would probably 
not be used unless the fighter threat increased ; 
however, it was considered to be a weapon which 
should be available for use at any time. The 
36th Squadron was fitted with a large number 
of jamming transmitters. Ten B-24's were each 
equipped with nine APT-l’s and one ARQ-8, 
with the barrage frequency distributed accord- 
ing to plan to cover both narrow and wide 
beams over the frequency range of from 80 to 
200 me. These aircraft were to be flown about 
80 miles from the Dutch coast, 9 miles apart, 
at a 15,000-ft altitude. This screen was not used 
except on an experimental basis. 


THE OPERATIONAL USE OF RCM IN THE ETO 


295 


In connection with the radar screening proj- 
ect, an intercept program was undertaken by 
the Air Forces to determine, as accurately as 
possible, what radar stations were being used by 
the enemy to provide EW. A Ferret aircraft 
was equipped with APR-4 and S-27 intercept 
receivers and was flown on a number of mis- 
sions during the assembly period of the 8th 
Air Force bombers, and enemy signals and fre- 
quencies were then recorded. Since the German 
EW net continued to spread in frequency and 
the number of different types of radar equip- 
ments which were used for this purpose con- 
tinually increased, the obtaining of such in- 
formation was important in order to insure 
reasonable performance from the screen. 

In order to overcome the possibility that the 
enemy might profit from our own v-h-f com- 
munications during assembly periods, a com- 
munications screening project was undertaken 
by the 8th Air Force with laboratory aid. Ex- 
periments were run which determined that our 
own very high frequency could be jammed in 
such a way as to prevent reception at a long 
distance by enemy intercept stations on the 
Dutch coast, while permitting normal traffic 
between the aircraft and the ground during the 
rendezvous. Five B-24 aircraft were provided 
for the purpose and each carried 12 SCR-522 
v-h-f communication equipments which were 
noise-modulated by Gastons (ARA-3’s). This 
v-h-f screen was flown regularly after it was 
completed. 

In October 1944, ABL-15 was requested by 
the Ninth Air Force to provide improved equip- 
ment for their enemy v-h-f listening (Y) sta- 
tions. Several Fuge 16 receivers with 60-c power 
supplies for ground operation were provided 
and installed. 

The British were the first to work on the de- 
vice called Perfectos, which was intended to 
trigger the German identification friend or foe, 
permitting the range and direction of German 
fighter aircraft to be found by Allied fighters. 
Homing facilities were provided so that an 
interception could be made. ABL commenced 
work on this development early in 1945 to 
modify it for use by the Eighth Air Force, 
whose requirements differed from those of the 
RAF in that a considerably increased range was 


desired, and installations were wanted in Amer- 
ican fighters. The Perfectos transmitter was a 
modified SCR-729, and the power output was 
increased to 5 kw from the original figure of 
about 750 w by adding a modified unit from a 
Navy ASB radar. A new homing antenna sys- 
tem was designed by the antenna group and 
was found to be very satisfactory. Ranges of 
80 to 100 miles were obtained on test flights. 
The first aircraft to go into operation was a 
Mosquito, which had been chosen because it was 
expected that the development could be com- 
pleted sooner on this aircraft. Unfortunately, it 
was shot down by friendly fighters over enemy 
territory on its second mission. A two-seater 
P-47 was next fitted with a Perfectos equip- 
ment. It was flown operationally and was prob- 
ably responsible for the location and subsequent 
destruction of two ME-262’s. Further opera- 
tions were unsuccessful as a result of lack of 
enemy fighter opposition. An installation of 
Perfectos in a two-seater P-51 was just com- 
pleted as World War II ended and therefore did 
not go into operational use. 

Another successful development which was 
completed too late for operational use but which 
might have had some application in the Pacific 
war, was the project Curtain. This was a de- 
vice, installed in a two-seater aircraft, for hom- 
ing on enemy v-h-f and Benito transmissions. 
A German Fuge 16ZY homing receiver was 
used with the normal loop and stub antennas 
replaced with three vertical quarter- wave Whip 
antennas which were so located and phased as 
to give the same pattern as the loop and stub. 
This arrangement was used in order to obtain 
maximum sensitivity, which was felt to be an 
essential. A successful homing range of over 
200 miles was obtained with this equipment. 


Miscellaneous 

In connection with the RCM activities in the 
ETO, several problems arose which were not 
directly related to countermeasures against flak 
or fighters. This section of the report intends 
to summarize the work done on two of the most 
important of these miscellaneous problems. 

One of the developments related to RCM has 


296 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


been, in all theaters of war, the work on meth- 
ods to decrease the vulnerability of the Allied 
sets to enemy jamming. One typical example is 
given by the work on the v-h-f transmitter used 
by all Allied aircraft. Complaints were received 
at the end of 1942 from several units of the 
American Air Forces that the SCR-522 trans- 
mitter was quite often seriously jammed over 
enemy territory. An investigation proved that 
the jamming might have been unintentional in 
that it was coming from the German Freya 
radar station operating in the same frequency 
band. A study of the SCR-522 proved that it 
was particularly susceptible to this type of in- 
terference. It was found possible to improve 
the situation by a very large factor by making 
a simple modification to the receiver. This modi- 
fication involved changing some time constants 
in the receiver circuit and introducing a limiter 
to clip off pulses of particularly large ampli- 
tude. Eventually all sets used by all the U. S. 
Air Forces were modified according to the 
specifications of the American-British Labora- 
tory where the developments were carried out. 
A similar type of work was done on v-h-f ground 
and ship-borne stations. 

For the purpose of planning RCM operations 
a theoretical analysis of the parameters in- 
volved is seldom sufficient. It is, therefore, ex- 
tremely useful to test RCM methods and tactics 
against a captured or simulated enemy equip- 
ment so as to determine the best methods of 
interfering with its operation. Several tests 
were flown in the ETC against a captured Ger- 
man Small Wurzburg to determine the effective- 
ness of Chaff and Carpet. It would be beyond the 
scope of this report to give a detailed analysis 
of all the tests which took place. It is sufficient 
to state that tests were made in order to de- 
termine the optimum amount of Chaff and the 
effectiveness of some of the enemy’s AJ devices ; 
to determine the effectiveness of special tactics 
involving the use of Chaff and the effectiveness 
of Chaff bombs; to determine the optimum 
spacing between jammers in a barrage for dif- 
ferent altitudes and for different formations; 
and, finally, to determine the extent of protec- 
tion offered by all these tactics for different 
altitudes and distances of the formation from 
the radar set. 


Another test which may be singled out for 
special mention was one in which a special 
formation was flown by one of the wings of 
the 8th Air Force. This special formation had 
the purpose of increasing to the maximum pos- 
sible amount the concentration of aircraft over 
the target. The purpose of the test was not 
only to check the feasibility of such a tactic 
but also to determine what advantages would 
accrue to the use of RCM by increasing the 
number of jammers present, at a definite time, 
within the beamwidth of the enemy radar scope. 
All the tests mentioned above were completed 
with a variable degree of success. The overall 
result was to supply the RCM planners with 
the data necessary for their operation. These 
tests were also particularly useful because they 
furnished one of the best proofs of the efficiency 
of RCM and therefore provided a basis for dis- 
cussing the necessity of the RCM program with 
operational personnel when no other proof of 
the usefulness of RCM was forthcoming either 
from intelligence or from the analysis of battle 
damage figures. 

At the end of the war in Europe a series of 
tests was conducted in ETO in order to supply 
information to the RCM operational theaters in 
the Pacific. The Japanese employed a gun-lay- 
ing set which was copied from the British GL 
Mark II. It was, therefore, decided to simulate 
tactics employed in the Pacific Theaters against 
one of these original British sets. 

With the help of civilian technical advisers 
and the cooperation of the British units, the 
Eighth Air Force conducted a long series of 
tests to determine the effectiveness of Rope 
and electronic jammers against the set. The 
data obtained were invaluable in supplying 
quantitative analyses of the effectiveness of all 
these sets and were used in the last month 
of war against Japan in order to help formulate 
the tactics flown by the 21st Bomber Command 
against the heavily defended targets of Japan. 

The German development of AJ devices was 
known to have included means for taking 
advantage of a jammer antenna of the type 
which was originally used and which produced 
vertically polarized signals. This development, 
called Stendal B by the Germans, was intended 
to permit measurement of range with the Wurz- 


THE OPERATIONAL USE OF RCM IN THE ETO 


297 


burg antenna cross-polarized with the jammer 
antenna. Fear of this development caused the 
circularly polarized AS-69 Fishhook antenna to 
receive a great deal of consideration and it 
was deemed very advantageous for use in the 
Carpet program. In addition, since the field 
pattern of this antenna was felt to be more 
suitable than that of the stub antenna used 
previously, it was felt highly important to use 
the antenna in the Eighth Air Force Carpet 
program. Since the fishhook antenna was not 
available in quantities from the United States 
in April 1944, it was decided to manufacture 
it at the Air Corps Base Air Depot. ABL-15 
simplified the design of the antenna and a large 
number were produced in the theater and were 
later supplemented by production antennas 
from the United States. 

In November 1944, field patterns which were 
taken of the AS-69 antenna showed an appre- 
ciable variation from the ideal pattern over 
the extended Wurzburg frequency range which 
was being encountered at that time. Modifica- 
tions to the antenna were made which per- 
mitted its use in the range 450 to 500 me. A 
considerable number of modification kits were 
later made in the theater at the base air depot. 


14.7.5 Effectiveness of the RCM 

Program 

An abstract of the ABL report®^® evaluating 
the flak countermeasures program of the air 
forces is included below. 

At the end of the war in Europe, ABL, the British 
branch of the Radio Research Laboratory, participated 
in an intelligence program whose main objective was 
to determine the effectiveness of the radar counter- 
measures program that was carried out by the Ameri- 
can heavy bomber forces against the German Flak 
radar. In connection with this program, information 
on the German scientific organization, German radar, 
and Japanese liaison was collected. The sources of in- 
formation were : interrogations of German officers 
responsible for Flak defense, interrogations of German 
Flak radar operators, interrogations of German scien- 
tists in charge of work on radar and anti-jamming 
problems, interrogations of engineers in charge of radar 
development in industry, inspection of German radar 
research laboratories and service installations, and 
examination of numerous German documents. 


German Flak Organization. The German Flak de- 
fense utilized about 16,000 heavy Flak guns and about 
3,000 Flak-control radars, Wurzburgs and Mannheims. 
The “normal” battery was comprised of four to eight 
guns, the larger guns (105, 128mm) being used in 
smaller groups than the 88 mm guns, and a control 
center. The “gross” battery, a combination of two to 
six normal batteries, had a correspondingly larger 
number of guns and, in addition, had at least two 
complete control installations. A control installation 
included optical and radar tracking gear and a 
prediction-computer unit. Radar-range and visual-angle 


Figure 10. Dual installation of fishhook an- 
tennas on the belly of a B-24. Such an antenna 
was intended to deliver circularly polarized jam- 
ming energy at relatively low angles to the 
horizon in the Wurzburg frequency bands. 

tracking was used whenever conditions permitted al- 
though when the radar was jammed, complete optical 
tracking was required. This, of course, was impossible 
under overcast conditions and a makeshift Flak proce- 
dure known as “directed barrage” was then employed. 
At a very limited number of target areas, extensive 
and accurate equipment was employed for transmitting 
and converting data for use at remote locations. Gen- 
erally, the substitute Flak-control procedures were 
much less effective than full tracking control. 

German Scientific Organization and Radar Research. 
Radar research started in Germany in 1934 and in 1936 
contracts were awarded to several manufacturing con- 
cerns for the development of operational radars. How- 
ever, no radar production resulted until 1938. Large 
scale production of the Wurzburg, which was the stand- 
ard Flak-control radar throughout the war, started in 
1940. All the early radars operated at frequencies below 
600 Me, and no significant work on research in the 
centimeter band was started until about 1943. Around 
the end of 1940, the High Command evidently decided 
that the war would be won in a short time and that 
existing radars and other scientific equipment would be 
adequate for a short war. As a result they stopped all 




298 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


research which would not produce finished weapons in 
less than a year and drafted many of the scientists into 
the Army (some exceptions existed, such as rocket, 
atomic explosive, and jet aircraft research). This policy 
was in effect until early in 1943, and as a result research 
stagnated. 

In January 1943, the first Allied cm. radar equipment, 
the British H2S system, was captured. The High Com- 
mand was taken entirely by surprise at the appearance 
of cm. radar equipment and evidently was not aware of 
the status of Allied radar research. At about the same 
time they evidently realized the war was going to be a 
long and hard one and decided that research must be 
revitalized and reorganized. As a result a Bevollmach- 
tiger (Plenipotentiary) was appointed for each of sev- 
eral branches of science. This man had absolute control 
of all research work done in his field. Radar and anti- 
jamming research were under the control of the 
Bevollmachtiger fur Hochfrequenz Forschung (Plenipo- 
tentiary for high-frequency research). A committee 
known as the SKFM (Special Committee for Radar) 
was also set-up under the Ministry of Armament and 
War Production which controlled the overall radar and 
anti-jamming problem, coordinating operational require- 
ments, research, development, and production. 

During 1943 most of the efforts of the BHF were 
expended in expanding research facilities and copying 
the British H2S, and as a result very few new devices 
were developed. However, at the beginning of 1944, the 
first copies of the H2S were completed and work was 
started on the design of a complete line of 9 cm. radars. 
About the same time they received another shock with 
the capture of our H2X, 3 cm. radar equipment. Imme- 
diately work was started on investigation of 3 cm. tech- 
niques. Later in the year they learned from intelligence 
sources of Allied work on equipments in the 1.0-1. 5 cm. 
band and again they started new work at wavelengths 
of 1.5 to 1.0 and this time also at 0.8, 0.7, 0.6, and 
0.5 cm. Early in 1945, the first experimental 9 cm. GL, 
AI, etc., equipments were completed, but the war was 
over before any appreciable number were placed in 
service. 

In general, the German radar program may be de- 
scribed as a frenzied attempt to catch up with the 
Allies. However, they never succeeded in producing 
any significant number of operational equipments, and 
hence, in spite of the tremendous effort expended, the 
program was a failure. In general, the state of technical 
radar development at the end of the war was similar to 
that existing in Allied laboratories in about 1942. 

Radar Countermeasures War. H2X and RCM were 
partners in the blind bombing attacks on Germany. 
ROM’s job was to “blind” the German Flak radars and 
hence keep the Flak losses down to a value which made 
blind bombing practical. Both were introduced in the 
bombing war against Germany at approximately the 
same time and were used together throughout the war. 
RCM also was used during visual missions to deny the 
Germans the accurate range information obtainable 
from their unjammed radars and force them to use 


optical tracking alone. The following paragraphs pre- 
sent a brief resume of the RCM war. 

The Germans first considered the use of Window, 
Chaff (dipole confusion refiectors), as a means of jam- 
ming radars in 1940, but immediately decided they 
would stand to lose a lot more than they would gain 
if the Allies used it against them. As a result they used 
“Ostrich” tactics and kept it under cover hoping the 
Allies would not think of it. In 1942, they conducted 
a few tests on Window and evidently confirmed their 
suspicions as they kept the matter more secret than 
ever. They made no plans for the development of anti- 
jamming devices against Window for their radar, and 
as a result were caught entirely by surprise and un- 
prepared when the British first used it against them 
on July 25, 1943. The Window completely jammed their 
radars at first and caused a tremendous amount of 
excitement in military circles. As a result the develop- 
ment of anti-Window devices was given the highest 
priority, and a very large number of scientists were 
put to work on the problem. 

The RCM war developed into a battle of attack and 
counter-attack, this battle being opened with the attack 
represented by the first British use of Window. Succes- 
sive “offensives” in the case of the U.S.A.A.F. were 
introduced with the first use of Carpet, October 1943; 
and the first use of combined Carpet and Window, 
December 1943. A gradual build-up of the Window pro- 
gram through the Summer of 1944 led up to the last 
all-out RCM offensive — the full scale application of 
Carpet and Window from Fall 1944, to the end of the 
war. 

German counter-offensives were, in general, efforts 
to patch up their Flak control radars to enable opera- 
tion through our jamming. As the battle developed, 
there were sufficient changes in the jamming due to the 
introduction of new jamming and due to the general 
increase in jamming intensity to render the Germans’ 
anti-jamming efforts virtually ineffective. The Germans 
themselves felt they were always one step behind and 
never succeeded in catching up with U.S.A.A.F. jam- 
ming. After the start of the full countermeasures pro- 
gram in Fall 1944, the German radars were almost 
useless. 

A tremendous amount of scientific effort was ex- 
pended in trying to overcome the effects of Allied 
jamming, but it was practically all in vain. From the 
Fall of 1943 on, an average of 50 per cent of the 
technical personnel engaged in high-frequency research 
worked on the anti- jamming program. In the late 
Summer of 1944, this figure probably approached 90 per 
cent. In all about 5,000 technically trained persons were 
engaged in high-frequency research, and therefore an 
average of about 2,500 were working on anti-jamming 
devices. Almost the entire remainder were engaged in 
cm. radar research. 

From German reports, the combined use of Carpet 
and Window jamming was by far the most effective as 
usually some anti-jamming device would help somewhat 
against either when used alone. 


UNITED STATES AID TO THE RCM PROGRAM OF THE RAF 


299 


RCM Effectiveness. An average of a number of 
German estimates on the overall reduction in the effec- 
tiveness of radar controlled Flak from September 1944 
on, reveals that the use of RCM by the American heavy 
bomber forces reduced the overall effectiveness to about 
one-quarter of the value obtained in the absence of 
jamming. In the case of the U.S. 8th Air Force, about 
40 per cent of the strategic missions flown in this period 
were under 8/lOths or heavier cloud cover, which means 
that the reduction of radar Flak effectiveness was, in 
the overall program, of major importance in saving 
bombers and crews. Before September 1944, jamming 
was having an important effect on German Flak, but 
it has not been possible to obtain estimates as to the 
extent of the effect in this earlier period. It can be 
concluded with certainty that RCM had a marked suc- 
cess in protecting heavy bombers on daylight raids, 
particularly on those runs under blind conditions. 

14.8 UNITED STATES AID TO THE RCM 
PROGRAM OF THE RAF 

14.8.1 Work of the First United States 
Technical Group 


Late in 1942, a number of engineers from the 
Radio Research Laboratory and the Radiation 
Laboratory were sent to England, to assist the 



Figure 11. German night fighter aircraft with 
antenna array for one of the later models of 
Lichtenstein, AI type radar. 


British with their RCM program and to pro- 
vide liaison between the British and the Amer- 
ican Laboratories. The first of the group 
arrived in England in November 1942 and were 
assigned to Telecommunications Research 


Establishment [TRE], RAF; to Admiralty 
Signal Establishment [ASE], Royal Navy; 
and to Air Defense Research and Development 
Establishment [ADRDE], Army. These men 
immediately commenced work on projects in 
the British laboratories very much on the same 
basis as the regular research staff members of 
these institutions. The more important projects 
on which this group worked and the operational 
use to which the equipment was put are briefly 
summarized below. 

Boozer 

Boozer was a code name applied to a simple 
warning receiver operating in the German AI, 
GL, and GCI bands in the vicinity of 500 me. 
The receiver was intended to provide the Brit- 
ish night bombers with a warning of the 
presence of enemy radar by means of simple 
indicator lights, thus permitting evasive action 
to be taken at the correct moment. The British 
Boozer was widely used during the great night 
bombing offensive in 1943, although its useful- 
ness was difficult to assess. 

Bagful 

This receiver was designed to search for and 
automatically record radar signals. The first 
operational use of Bagful was by the 8th Air 
Force, and this receiver played an important 
part in the initial American investigation of 
German radar. 

Air Cigar 

One of the most important of the British 
RCM operations was that known as Air Cigar. 
In this operation, jammers were carried in 
several of the night bombers to disrupt the 
v-h-f communications used by the enemy in 
his night fighter GCI system. A receiver which 
provided means for rapidly setting the jammers 
on the enemy's frequency was developed. This 
receiver provided a panoramic presentation of 
the enemy communication band and by means 
of a marker pip permitted the operator to set 
his jamming transmitter exactly on the enemy 
channel. The Air Cigar operation was used 
extensively, beginning in the fall of 1943, and 
was generally conceded to be extremely suc- 
cessful. 


300 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


Carpet II 

This was a jamming transmitter designed 
for the purpose of automatically searching for 
and locking on enemy radar frequencies. A 
discriminator circuit developed in conjunction 
with this apparatus which permitted the trans- 
mitter to be set precisely to the center of both 
weak and strong signals was subsequently used 
in other applications, including Bagful. Carpet 
II was produced and used on a large scale on 
small landing craft in the invasion and later 
was also employed in the British night bombers 
to supplement Window. 

Although the direct participation of this 
initial technical group in the RCM program of 
the RAF was discontinued when the American- 
British Laboratory was set up in the ETO, an 
exchange of RCM technical assistance and 
equipment between the Americans and the 
British continued throughout the rest of World 
War II. 


Big Ben 

The German V-2 rocket was given the code 
name Big Ben. The defense of Britain against 
Big Ben was primarily a British problem and 
was the responsibility of the RAF. However, 
American equipment and technical aid also 
played a part in the program. In the initial 
phase of the Big Ben scare, very little was 
known about the weapon. It was felt to be a 
potential threat of great importance against 
Britain, and for that reason very high priority 
was placed on any measures designed to operate 
against it. Initially, then, so little was known 
about the problem that any and all measures 
which appeared to have chance of success were 
taken with the utmost possible speed. 

A series of listening stations along the east 
coast of Britain were alerted and put on con- 
stant guard against Big Ben control signals. 
The British 192nd Squadron conducted regular 
flights in an attempt to correlate sightings of 
the rocket with actual signals heard. Equip- 
ment recovered from rockets which landed in 
Britain was examined with extreme care. From 
these analyses, some successful reconstructions 
of the equipment functions were made. 


A number of h-f transmitters varying in 
power output from 10 to 50 kw were modified 
to operate on the suspected Big Ben control 
signal frequencies and were set up along the 
probable line of flight of the rocket, assuming 
that London was the main target. The 50-kw 
Elephant Cigar, which was an American trans- 
mitter, was modified so that it would cover the 
probable Big Ben frequencies and also so that 
it could be tuned quickly as a spot jammer. 
Several 50-kw transmitters were obtained from 
America, and a number of American 15-kw 
equipments, which were originally designed to 
jam the German v-h-f band, were delivered and 
modified for possible Big Ben jamming. 

The initial phase of the Big Ben problem 
involved doing the best possible job in search- 
ing for the radio signals which presumably 
were used by the enemy for a number of 
purposes connected with the precise control of 
the rocket. This search job proved to be an ex- 
ceedingly difficult problem because of the very 
short duration of the transmissions and because 
of the fact that, at least in the early phases of 
the work, the search had to be done from air- 
craft because of the improbability of receiving 
any signals in England on the ground. Most of 
the attempts to intercept the signals were not 
successful and actually the knowledge concern- 
ing the control signals was obtained from the 
analysis of equipment which had crashed. 

Fortunately, the advance of the ground 
armies eventually greatly reduced the im- 
portance of the Big Ben threat, and, as this 
occurred, the priority on countermeasures 
dropped accordingly. 


Tuba 

The Tuba project is an example of an opera- 
tional need stimulating the development of a 
completely new technique which progressed to 
operational use. For this reason, despite the 
fact that the operational importance of the 
device was much lower than generally expected, 
it is worth while to outline briefly the history 
of this program. 

By the summer and the fall of 1942, the 
Germans were using their Lichtenstein AI 


UNITED STATES AID TO THE RCM PROGRAM OF THE RAF 


301 


radar on their night fighters over Germany and 
German-occupied territory with sufficient 
effectiveness to be an important factor in the 
losses sustained by the RAF Bomber Command. 
The low power of the enemy AI and the rela- 
tively poor antenna system, plus the fact that 
the receiver was of superregenerative type, 
made the use of electronic jamming appear 
attractive. Jamming of the enemy AI could 
be carried on from ground bases with powerful 
jammers, by jammers carried in all of the 
bombers, or by use of medium-power jammers 
in especially equipped airplanes flown for that 
purpose along the bomber trail. The second 
alternative did not appear attractive because 
of the danger that the enemy could home on 
the jammer carried by the bomber. The other 
two alternatives were both considered and 
employed. 

The first example of jamming the enemy 
AI from the ground took place during the 
middle of 1942, when the RAF set up a series 
of jammers with power of the order of 50 to 
100 w and with a rotatable high-gain direc- 
tional antenna. These jammers were monitored 
from the ground by listening to the enemy 
signals and by tuning the jammers on the fre- 
quency which appeared active. 

This system had several shortcomings, and 
therefore the idea was suggested that a power- 
ful ground-based jammer could be built to 
cover the whole band of the enemy AI radar 
set. It was also required that the jamming 
power be sufficient to jam enemy sets within 
a wide angle from the ground base. It was 
easy to see that powers of the order of magni- 
tude of 15 to 50 kw were required for the job. 
Such a power, at frequencies of the order of 
magnitude of 500 me, had never been obtained 
before. Actually, even powers of the order of 
1 kw were far from practical realization. It so 
happened, however, that the NDRC had been 
sponsoring the development® of a special tetrode 
oscillator.^ This tube seemed capable of giving 
the power required and the needs expressed by 
the British Bomber Command were strong 


e By Dr. David Sloan, then of the Westinghouse Re- 
search Laboratory. 

^ Originated by Dr. Sloan and Dr. L. C. Marshall at 
the University of California. 


enough to make the whole program worth 
while. 

The development of a transmitter using this 
tube was done at the Harvard Radio Research 
Laboratory. The jammer was to deliver about 
50 kw and two transmitters were required with 
a total bandwidth of about 10 me each, so that 
two units could cover the whole enemy 20-mc 
band. Together with the AI jamming, a 
high-power communication jammer was also 
designed to interfere with the enemy ground- 
to-air and air-to-ground communications. It 
was found very difficult to obtain a wide-band 
modulation of the Sloan tube, but powers of 
the order of magnitude required could be 
achieved with a continuously pumped tube. 
The first unit had two 25-kw transmitters and 
was mounted in six trucks. The British were 
supposed to take care of the construction of 
the antenna, but for several reasons no antenna 
was available when, in February 1944, the 
first complete unit was shipped from Boston 
to England. The equipment was made opera- 
tional 3 or 4 weeks after its arrival in Great 
Britain and, since the antenna problem had not 
been solved, it was necessary to improvise a 
horn made of chicken wire. By mid- July 1944, 
operational use of the equipment had begun. 
Crews were trained and the American civilian 
technical crew returned to the United States. 

In the late summer of 1943, it had become 
apparent that an obvious German reaction to 
the use of any AI jammer would be to shift 
the frequencies either up or down. For this 
reason, new tubes were designed to cover fre- 
quencies from 345 to 375 me and from 470 to 
540 me. A new Model IV was subsequently 
built tunable on the whole range of 350 to 600 
me. This new tube was also easier to modulate. 
With the new tubes available, one of the two 
new units which were being prepared for the 
British had to be equipped with the broad-band 
tube. Work on making the second and third 
units operational began in July 1944. By Janu- 
ary 1945, the two new units were completed and 
three units were available in England. 

During the summer of 1944, the first Tuba 
equipment was used operationally on a more or 
less regular schedule operating several hours 
a day and several times a week in coordination 


302 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


with bomber command operation. Operational 
use was stopped in October 1944, because the 
enemy had ceased any extensive use of the 
500-mc AI in favor of a set operating at a 
much lower frequency. It must be noted, how- 
ever, that the operation of the equipment was 
satisfactory in all respects and this is signifi- 
cant if one considers that never before had 
power of the order of magnitude of 15 or 20 
kw been available in the 500-mc band. 

As noted before, the operation of the first 
Tuba unit was interrupted in October 1944, 
long before the second and third units arrived 
in England. Neither of these two units was. 


Tuba transmitter (Figure 12) should have 
been effective in jamming AI sets operating 
within 1 or 2 me of its carrier at distances of 
200 miles or less from the jammer. 

9 NAVAL RCM 

^ Use of RCM in Early Naval 
Operations 

The use of RCM by the U. S. Navy was 
extensive and had the following purposes. First 
of all, it involved countermeasures against 



Figure 12. The wave-guide “switch yard” of the high-power, ground-based jamming transmitter, Tuba. 


therefore, used, but plans had been made for 
moving one of them to the European continent 
when World War II ended. 

It is difficult to evaluate the effectiveness of 
the Tuba project. The Tuba became operational 
just at the time when the Germans were 
changing from the Lichtenstein to the much 
superior SN-2, which operated at 90 me, out 
of the frequency range of Tuba. However, tests 
carried on in this country did show that a 


guided missiles launched by enemy aircraft in 
attacking Allied shipping. Second, it involved 
the use of countermeasures and radar deception 
both for the purpose of diversion and for pro- 
tection against detection and radar fire control 
by the enemy. Deception was used to simulate 
landings behind the enemy lines in support of 
a ground attack, in order to capture isolated 
islands by giving the enemy the impression that 
a large force was concentrated in the surround- 


NAVAL RCM 


303 


ing waters, and was finally employed as an 
important part of the overall plan in the 
invasions of Normandy and southern France. 

Guided Missiles 

In 1941, British Intelligence gave the first 
news of the development of guided missiles by 
the Germans. The first experimental models 
developed by the enemy were found to be 
successful about the middle or end of 1942. 
The first example of successful attack by the 
glide bombs Hs-293 was when corvettes in the 
Bay of Biscay were attacked in 1943 while on 
an antisubmarine patrol. One of these corvettes 
was sunk and another was damaged. In October 
1943, two special destroyer escorts were 
equipped by the U. S. Navy, on a very high 
priority, with search and jamming equipment 
in the band in which the enemy was expected 
to be operating. These destroyer escorts were 
sent to the MTO ; they were attacked in Novem- 
ber off the Algerian coast. Intercept signals 
were correlated with the attack, and informa- 
tion was obtained on the frequency and the 
type of modulation employed. More equipment 
was developed and built, and more ships were 
equipped with it. In the winter of 1943-1944, 
the number of RCM sets employed increased, 
so that in February 1944 all the convoys from 
Oran to Bizerte had at least two ships equipped 
with guided missile jammers to accompany 
them. After that, no ship in any protected con- 
voy was hit by glide bombs. A little earlier, 
in January 1944, when the invasion at Anzio 
took place, the two original jammer ships were 
present. The enemy made 75 separate attacks 
against the Allied shipping concentrated near 
the beachhead; about 125 control signals were 
jammed in a 2-month period. Five ships were 
hit, but two of these were not in the immediate 
area of the destroyer escorts. 

The number of ships equipped with jammers 
during the year 1944 increased continuously. 
Frequent reports were obtained of guided 
missile signals successfully jammed. Alto- 
gether, the percentage of hits dropped to the 
level of ordinary high-level bombing. During 
the invasion of Normandy and southern 
France, several glide bomb attacks were re- 
ported, most of which missed. Several examples 


were reported of glide bombs, headed directly 
for ships, which broke off under jamming and 
crashed into the sea. 

Intelligence reports received after V-E Day 
contained claims by the Germans that Allied 
jamming had not been the major cause for 
the disappearance of the enemy’s guided missile 
attacks. They claimed that the real reasons 
were (1) that Allied air superiority prevented 
the parent aircraft from flying close enough to 
the targets and (2) that lucky hits by one of the 
attacking strategic air forces had destroyed 
all the aircraft equipped with the necessary 
installations and these were found very difficult 
to substitute. It is well known that the strategic 
situation of the enemy air arm deteriorated 
continuously during the year 1944, and it is 
clear that all of the above factors combined to 
make the danger of guided missiles less serious 
than it originally appeared. One result trace- 
able to the use of countermeasures was that 
enemy scientists responsible for the develop- 
ment work became prejudiced against any type 
of radio control which was not very carefully 
protected against Allied jamming. The enemy 
development of new weapons was thereby 
slowed down considerably and the equipment 
designed became very complicated and difficult 
to build. By the end of World War II, no newly 
developed guided missile had seen operational 
use against Allied ships. 

Deception 

As mentioned before, several operations 
were carried on in which RCM deception played 
an important part. A special Navy force was 
equipped with RCM sets and deception devices 
consisting of barrage balloons, corner reflec- 
tors, and so on. This force is credited with 
capturing islands off the coast of Italy. A few 
boats, carrying countermeasures sets (inten- 
tionally made not completely effective) and 
deception devices of all descriptions, were able 
to simulate the existence of a force comprising 
battleships and other large vessels. As they 
approached the islands, surrender was re- 
quested from the enemy and was obtained 
solely on the basis of a bluff supported by the 
indications appearing on the enemy’s radar 
scope. This tactic, originally used for the cap- 


304 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


ture of islands off the coast of Naples, was 
repeated to simulate the approach of a landing 
force at a point north of the real beachhead 
at Salerno. This particular deception is 
credited with delaying by several days the 
operational employment of one of the enemy’s 
crack divisions against our invading forces. 
The same small force was also employed in the 
first part of 1944 to simulate another landing 
north of the Anzio beachhead; the purpose of 
this tactic was to help the ground forces attack- 
ing from the south in joining the forces which 
had remained on the Anzio beachhead for sev- 
eral months. 

A substantial RCM effort was also carried 
on to protect the main invading force at 
Salerno. Here the purpose was to use counter- 
measures to hide the exact spot of landing 
during the night before D-Day, though it could 
not hide the fact that an operation was impend- 
ing. A large number of Rug transmitters were 
sent from the United States by very high 
priority. These sets arrived in Africa 5 days 
before the operation and were installed to pro- 
tect seven convoys by jamming the enemy coast- 
watcher frequency band. One evidence of their 
effectiveness was that several batteries of Ger- 
man 88’s near Salerno were firing very wildly, 
and, in fact, shells were fired over the convoys 
and landed on the opposite shore where there 
were some German troops. 

When the island of Elba was invaded, a 
strong diversionary effort was carried on along 
the northern shore in support of the amphibious 
force which attacked from the south. PT boats 
carrying balloons, corner reflectors, and RCM 
jammers approached the northern shore under 
cover of a dense smoke screen. Sonic devices 
with very powerful loudspeakers simulated the 
noise of landing boats approaching the beach 
and of tanks coming out of them. Rocket fire 
was directed against the shore positions and 
dummies were dropped on the surf to simulate 
the landing of infantry. 


14.9.2 Invasion of Normandy 

The naval RCM plan of the operation Nep- 
tune, as the invasion of Normandy was called. 


was the result of a great deal of study by the 
British and American operational groups and 
technical personnel. 

The enemy coastline, particularly in Nor- 
mandy, was very well protected by a number 
of radar chains which were designed to supply 
EW facilities and GL information to coastal 
batteries. In addition, enemy ASV was also 
dangerous to the success of the operation. 
Therefore, the use of RCM against the enemy 
coastal and airborne radar was a potentially 
important part of the naval invasion program. 

The operational program from the naval 
RCM standpoint could be broken down into 
two parts: first, RCM could be applied in such 
a way as to deny the enemy information con- 
cerning the time and location of the attack and, 
in addition, feint attacks could be made feasible 
by proper application of countermeasures ; sec- 
ond, as soon as the ships were within range of 
the shore batteries, enemy fire-control radar, 
which was a potentially serious threat, could 
be neutralized by RCM. 

Prior to the invasion of Normandy, all the 
known radar stations along the enemy coast 
were subjected to direct attack by strafing and 
rocket fire. This was done over an area suffi- 
ciently large to divert suspicion from the 
chosen landing beaches. 

The locations of the enemy radar stations 
were obtained by several methods, such as in- 
telligence, photo-reconnaissance, and the taking 
of DF fixes. British listening stations supplied 
a great part of the information, and the British 
set up, at appropriate points along the coast 
of England, special DF-ing equipment known as 
Ping Pong, which was capable of obtaining 
very accurate fixes on enemy radar signals. In 
addition, the British attempted to obtain more 
information concerning the German naval RCM 
by sending small boats equipped with search 
gear in toward the enemy coast within range of 
enemy radar. 

The main attack force was made up of both 
British and American vessels, and these forces 
went in to separate landing areas. The jammers 
were not turned on until shortly before the 
ships came within range of enemy radar. Jam- 
mers were carried in the attack forces, in 
landing craft, as well as in a number of battle- 


NAVAL RCM 


305 


ships, cruisers, destroyers, headquarter ships, 
and troop transports. In addition to the main 
attack, feints were made to the north and to 
the south. RCM equipment played a large part 
in these diversionary attacks, which were car- 
ried through by small harbor defense motor 
launches, and was effective in creating the im- 
pression that large forces were approaching the 
coast. In addition to these diversions. Window- 
dropping aircraft were used in support of the 
airborne landings. Such aircraft, by laying 
Window trails, attempted to confuse the enemy 
as to the location and direction of the airborne 
attacks. 

Protection of the attacking force from enemy 
coastal guns was a difficult problem, although 
it was simplified considerably by the direct 
attacks which had been made on the radar 
stations. The magnitude of the RCM effort was 
largely determined by the availability of the 
jamming equipment. The power required to 
self-screen a big surface vessel rapidly becomes 
very large as the ship approaches the radar 
station, and it was impossible, therefore, to 
give complete protection to all ships in the 
attacking force. Low-power Carpet II jammers 
with an output of 1/2 w, adjusted to cover the 
Seetakt and Wurzburg bands, with a few Man- 
drel, Carpet I, and Rug jammers, were placed 
in the landing craft partly for self-protection 
and partly in the hope that when they were 
close to the beach some screening of the trans- 
port area would result from jamming through 
the side lobes of the enemy radar. The Mandrels 
were set to known frequencies of the enemy 
stations, these frequencies having been care- 
fully measured prior to the operation. Likewise, 
Rug and Carpet I jammers were used to provide 
a barrage across the most probable enemy fre- 
quencies. Pimpernels (used only on British 
ships) and Carpet IPs were adjusted to search 
the bands from 530 to 590 me, 460 to 508 me, 
and 330 to 400 me, each set covering a selected 
40 me, of these ranges. 

In the Neptune operation, it was necessary 
for both the United States and British Navies 
to rely for the most part on RCM equipment 
which was originally designed for aircraft in- 
stallation. In the U. S. ships, only 12 out of the 
88 radar jamming equipments which were in- 


stalled were designed for shipboard use. These 
12 equipments were the relatively high-power 
Broadloom (CXFR) and TDY jammers, which 
were used on three battleships, two cruisers, 
two destroyers, a headquarters ship, and sev- 
eral troop transports. The complete schedule of 
fittings in American ships is shown in Table 4. 

Table 4. Schedule of fittings in American ships. 


Transmitter Installations 

Set LCTA LCTA-5 LCGL Total 


British Carpet II (h-f ) 

16 

7 23 

British Carpet II (1-f ) 

16 

3 19 

American Mandrel 

4 1 

4 9 

British Mandrel 

1 

1 

Carpet I 


10 10 

Rug 

4 

10 14 

Monitoring Installations 

76 

Frequency range covered 

USS Ancon 

1 S-27 with RBW pan adapter 

28-143 me 

1 APR-1 with TN-2 and RDK 

pan adapter 

2 APR-1 with TN-3 and RDK 

pan adapter 

80-300 me 

300-1,000 me 


2 RDL (Blinker) 250-450 me; 450-650 me 

1 APR-5 1,000-3,000 me 

2 Oscilloscopes (for pulse analysis) 

2 Beat-frequency oscillators (for pulse analysis) 

USS Tuscaloosa 

Same as above with the addition of the following : 

1 APR-6 3,000-6,000 me 


As previously mentioned, diversionary at- 
tacks were made with harbor defense motor 
launches. The attacks were not expected to be 
completely effective but were intended to add 
confusion. In order that the size of these diver- 
sions should be made to appear as great as pos- 
sible, the boats taking part towed balloons with 
corner reflectors, and aircraft dropping Window 
flew overhead in a zigzag course slowly pro- 
gressing towards the coast to give the appear- 
ance of a large invasion front slowly moving in. 
The jammers in these boats were so arranged 
that the probability of the enemy being able to 
look through the jamming screen was fairly 
great, although it was hoped that sufficient jam- 
ming would be present to add greatly to the con- 
fusion. 

These diversionary attacks were operated by 
the British and were thought to be a very real 
factor in adding to the general confusion that 
characterized the enemy’s planning at the time 


306 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


of the attack. Since enemy aircraft carrying 
ASV radar were a potential threat to the secur- 
ity of the diversions, the diversionary boats 
carried Moonshine equipment with a special 
operator so that enemy aircraft using radar 
would also see apparently large forces. During 
the operation several signals were heard by 
these Moonshine operators and apparently were 
coped with successfully. 

Since the equipment used in the RCM installa- 
tions was in most cases not designed for ship- 
board use and since there had been little previ- 
ous experience in the use of RCM on a large 
scale during an invasion, a great many new 
installation and equipment problems arose dur- 
ing the preparations for the Neptune operation. 
During several months preceding the operation, 
ABL-15 devoted a major part of its efforts to 
this work and was able to solve most of the 
problems that arose. 

In February 1944, work was commenced on 
the testing of most of the RCM equipments 
which were involved in the invasion. This test- 
ing was done under simulated operational con- 
ditions at the Admiralty Signals Establishment 
Extension at Tantallon, Scotland, with Amer- 
ican technical personnel participating. Since a 
large amount of American RCM equipment was 
used in the invasion, the British were eager to 
obtain assistance from men who were experi- 
enced with such equipment. Data were obtained 
at Tantallon on the jamming ranges of various 
equipments under different typical conditions, 
and problems of serviceability and installation 
were studied. Equipments which were tested at 
Tantallon included Peter, Pimpernel, Carpet I 
(APT-2), and Carpet III (APQ-9), Mandrel 
(APT-3), Dina (APT-1), Rug (APQ-2) , Broad- 
loom (CXFR), British Mandrel, and British 
Carpet II. 

Tests were conducted of Peter equipment in- 
stalled in a harbor defense monitor launch of 
the Royal Navy. The equipment was intended to 
function only as a signal-intensifying device in 
order to increase the apparent size, as seen by 
the enemy radar, of the ship carrying the 
equipment. It was hoped that the equipment 
could be used in a diversionary attack with 
small boats, which, by means of Peter, would 
appear to be cruisers. Tests of this equipment 


operating with a bandwidth of 20 me and a 
gain of about 300 me were fairly satisfactory, 
although the Royal Navy decided not to use 
Peter and the project was discontinued. In place 
of the proposed Peter operation, the diversions 
used balloons with corner reflectors and Win- 
dow-dropping aircraft. The use of these meth- 
ods minimized the importance of frequency 
spread of enemy stations. 

Three German radar sets (a small Wurzburg, 
Seetakt, and Freya) were available for testing 
at Tantallon, and with the aid of these it was 
possible to determine the jamming effectiveness 
of our equipments when carried on mine sweep- 
ers and destroyers. Equipment installation 
problems were studied at Tantallon to deter- 
mine whether, for example, British Carpet II, 
which was an automatic searching jammer, 
could be used on the same ship with American 
Mandrel or Carpet I. The results of these 
studies were too lengthy to give here, but from 
this experience it was possible later on to make 
suitable frequency allocations and to choose 
equipment locations on the actual ships which 
were to be involved in the invasion. 

One of the problems which was encountered 
at Tantallon in the actual ship installations is 
worthy of mention. The problem of fitting RCM 
equipment aboard ship is complicated by the 
likelihood that it will produce interference to 
other radar or radio equipment aboard the 
same or near-by facilities. Rather severe inter- 
ference was produced by the CXFR-TDY equip- 
ments, and interference somewhat less serious 
was also produced by the AN/APT-3, APT-2, 
and APQ-2. In the case of the CXFR-TDY 
the interference came from several different 
sources such as radiation from power leads 
carrying interference signals up to 15 me and 
direct radiation from the antenna of interfer- 
ence in the region of 30 to 150 me as well as 
in the vicinity of the output carrier. The first 
two types of interference were eliminated by 
suitable modifications to the equipment, but 
there was little that could be done about the 
interference in the bands adjacent to the oper- 
ating frequency, since it was found that the 
output spectrum of the transmitter was such 
that the energy was spread over a very wide 
band. 


NAVAL RCM 


307 


The U. S. Navy fitted two ships with com- 
plete monitoring facilities for continually check- 
ing the radar spectrum from 30 to 6,000 me 
for new enemy frequencies while the invasion 
progressed. Since a large percentage of the 
equipments were designed for airborne opera- 
tion, makeshift arrangements in fitting the 
equipments were necessary in many cases. 

A very essential part of the technical pro- 
gram was the training of the personnel to 
operate properly the jamming and monitoring 
equipments. ABL-15 aided in the training of 
a large number of Navy officers and technicians. 
In the case of the jamming transmitters, 
the training was mainly on the CXFR-TDY 
equipments where operators were required to 
monitor the enemy signals and manually tune 
the equipment to the enemy's frequencies. 

Although particular emphasis has been given 
in this report to the U. S. Navy RCM program 
in the Normandy invasion, actually British 
ships carried more RCM equipment and even 
more American RCM equipment than was car- 
ried by the U. S. vessels. 

American technical personnel also aided with the 
installation of RCM equipment in British ships. At a 
conference held in England, about the first of May 
1944, it was decided that ABL-15 because of its com- 
mitment to the United States Navy, could not supply 
sufficient personnel to the Royal Navy. As a result an 
urgent cable was sent from General Eisenhower to 
General Marshall asking that sixteen civilian techni- 
cians be sent to aid the British. Six days later, nine 
men from the Radio Research Laboratory and two 
from the Columbia Broadcasting System arrived in 
London. Shortly thereafter five additional men arrived 
from the Radio Research Laboratory. These men to- 
gether with personnel from the Admiralty Signal Estab- 
lishment went to work on the ship fitting program. Two 
hundred and seventy-four RCM equipments were in- 
stalled in British ships, distributed as follows :83i 

113 Carpet I 17 Pimpernels 

1 Carpet III 11 CXFR 

24 Rugs 11 Blinkers 

27 Mandrels 

It is very difficult to assess the result of 
countermeasures during the invasion of Nor- 
mandy. Although the attacks on radar stations, 
made by the air forces prior to the invasion, 
were undoubtedly very successful, it is known 
that in a few instances stations were able to 
continue operating. The evidence appears to be 


fairly good that in some cases jamming caused 
erratic shooting by the en6my coastal batteries. 
Enemy air opposition was practically absent, 
particularly duripg the daytime, and, although 
there are a few instances of the possible use, 
by the Germans, of radio-controlled missiles, 
there were no successful attacks, for which the 
jamming may have been at least partly respon- 
sible. 


14.9.3 Invasion of Southern 

France 

The role of RCM during the invasion of 
southern France was very similar to the one 
played during the invasion of Normandy and 
other amphibious operations of the same type. 
In order to achieve at least tactical surprise 
during the landing operations, RCM can be 
used to very good advantage for the double 
purpose of shielding the main attacking force 
and of misleading the enemy to believe that the 
attack is coming from a direction other than 
the real one. In order to achieve the second 
purpose, diversionary forces are usually em- 
ployed. During the invasion of southern France, 
there were three main attacking forces, two 
diversionary forces, and one so-called support 
force. As is well known, the three main attack- 
ing forces landed on the French coastline east 
of Toulon. The two diversionary forces at- 
tempted diversions, one east and one west of 
the main attack. The right-flank diversion ap- 
proached the region of Monaco prior to H-hour 
and attempted with corner reflectors, balloons, 
and jamming to create an illusion of a force 
approaching in that sector. The amount of RCM 
equipment allocated to this force was extremely 
small and it was fully expected that this force 
would be recognized as a diversion by the time 
it got within 20 miles or so of the coast. After 
this, the eastern force was to turn westward 
and eventually rendezvous with the western 
diversionary force near the main beachhead at 
about H-plus-2. The left-flank diversion, which 
operated in the Toulon area, included one de- 
stroyer and a number of motor launches and 
torpedo boats. Balloons, corner reflectors, Brit- 
ish Moonshine equipment, a slowly progressing 


308 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


trail of Window laid by Air Forces planes, and 
radar jamming were employed in these diver- 
sions. The RCM transmitters were monitored 
with APR-1 and used as spot jammers. On the 
night of D-minus-1, the western force was to 
follow a rather complicated course, eventually 
coming very close to shore just prior to H-hour, 
turning away again, then going eastward, and 
finally meeting the eastern force. It was in- 
tended that this force put on a really good 
spoof, and it was provided with more RCM gear 
than any other force except the main attacking 
one. The left-flank diversion operated on the 
night of D-minus-1 as planned. On D-night, 
however, bad weather prevented a repeat per- 
formance which was planned. 

The support force or Sitka force invaded the 
Island of Hyeres several hours prior to H-hour 
and captured the island. During the actual 
landing, five guided missiles were reported, one 
of which sank an LST. It is believed that the 
other four were definitely jammed and they did 
not hit any vessels. 

Direct action against enemy coastal radar 
was planned for the invasion of southern France 
just as it had been planned and used in the 
invasion of Normandy. Bombs, rockets, and 
gunfire were used against radar stations but the 
action was started too late to get substantially 
good results. 

To the jamming carried on by the ship-borne 
RCM sets, must be added that which was pro- 
vided by 10 Wellington aircraft of the British 
night-bombing group, each fitted with 5 Man- 
drel installations, or a total of 50 jamming sets, 
which covered the coastline on either side of 
the beach area. Beaver III from Corsica sealed 
in the jamming gaps left in the beach area with 
the use of ground-based jammers consisting 
of Dina-amplifier combinations. The listening 
watch carried on during the day of the invasion 
noted that the coast-watcher stations which 
were not jammed by either the Wellington air- 
craft or the ground-based sets were not effec- 
tively utilized by the enemy ; five out of six went 
off the air. 

It must be added that, in the region where the 
diversionary forces were supposed to simulate 
a landing, the enemy was allowed to operate 
at least during short intervals in order to make 


it possible for him to “see” the diversionary 
force. 

The RCM plan for the invasion was prepared 
by the RCM board, which had representatives 
of MAAF, AFHQ, the U. S. and the Royal 
Navies, and other interested agencies. The num- 
ber of RCM installations planned by the U. S. 
Navy for this operation was about twice the 



Figure 13. Members of the First Signal Serv- 
ice Platoon (Special) installing a modified 
AN/APA-24 direction-finding antenna in the 
mountains of Corsica for Beaver III mission. 

number of installations planned for the United 
States^ part of the invasion of Normandy. There 
were approximately 200 RCM installations 
either of the barrage or the manually tuned 
type. The larger proportion of the sets had to 
be preset on specified frequencies before the 
operation. This created a very serious problem 
for the persons charged with the problem of 


RCM IN THE GROUND FORCES 


309 


installation and operation of the set. On July 
25, 1944, which was about 18 days before the 
invasion, no RCM installation had been com- 
pleted in any U. S. ship, with the result that the 
majority of the work was compressed into a few 
days. 

Information and intelligence of the enemy 
stations were supplied by the coordinated analy- 
sis of the previous work of the Ferrets and of 
the British and American ground listening sta- 
tions. The work of analysis and specifications 
had been carried on by an appropriate office of 
the headquarters of MAAF. 

The installation of RCM equipment in all 
U. S. ships was a race against time. Despite the 
fact that the RCM plan was a satisfactory one, 
the actual implementation suffered greatly be- 
cause of the hurry. In the end, 95 per cent of 
the RCM installations originally planned were 
actually completed and set on frequency in 
some manner according to the predetermined 
plan. 

The total number of RCM transmitters in- 
stalled and set to frequency was about 260, of 
which about 80 were installed and operated on 
British ships and 180 on American vessels. Out 
of this total of 260, approximately 55 trans- 
mitters were manually tuned by operators with 
APR-1 receivers. The number of transmitters 
in the three main forces was about 210; the 
balance, or roughly 15 per cent, was in the 
support forces and in the two diversions. 

In the main forces, equipment was installed 
on the following classes of U. S. and British 
ships: 4 battleships, 2 transports, 12 cruisers, 
15 destroyers, 24 mine sweepers, 57 auxiliary 
mine sweepers, 2 mine sweep tenders, and 5 
landing craft. In the two diversions, RCM 
equipment was installed on 1 destroyer, 2 Brit- 
ish gunboats, 4 torpedo boats, and 4 sea-rescue 
launches. Air attacks against radar locations 
began on D-minus-5, but were hampered by bad 
weather and most of them were made from 
D-minus-2 to D-Day. According to some infor- 
mation available, after these attacks there was 
still an appreciable number of coastal radars in 
operation on D-Day, as indicated by monitoring 
stations. Several sites visited by intelligence 
personnel on D-plus-6-day did not show any 
sign of damage despite the fact that they had 


been allegedly attacked and rendered unopera- 
tional before D-Day. Despite the fact that the 
number of sorties fiown against radar stations 
was about 500 (as compared to about 1,400 for 
Neptune in Normandy), complete elimination 
of enemy radar by direct air attack was not 
achieved. This confirms the difficulty and un- 
certainty involved in this type of operation. 


10 RCM IN THE GROUND FORCES 

For reasons already mentioned, radar coun- 
termeasures were not used to a great extent by 
the ground forces in World War II ; a few note- 
worthy developments took place, however. In 
order to be prepared for work against possible 
enemy ground-based jammers, the U. S. Army 
Signal Corps equipped a number of vans with 
antennas and receivers capable of intercepting 
signals in the frequency band 100 to 1,000 me 
and of determining the direction of the incom- 
ing signal by means of DF-ing antennas. Micro- 
wave receivers were also available despite the 
fact that no enemy efforts in that frequency 
band occurred during the war. (The possibility 
of eliminating undesired interference or jam- 
ming by means of loop antennas was also con- 
sidered and typical antennas were built out of 
material available in the field.) 

At the request of the United States Twelfth 
Army Group, the ABL undertook the develop- 
ment of a device for simplifying radio spoofing 
operations. The device was patterned after a 
British development and was intended to simu- 
late (with one or more transmitters) the oper- 
ation of a normal Army communication set. 
The equipment was developed but not used op- 
erationally because World War II ended. It may 
be worth mentioning, however, that in this 
equipment (known by the code name of Elmer) 
the desired sequence of messages, consisting of 
normal traffic and replies from an Army net, 
was recorded on a magnetic wire tape. Since 
in a normal situation the various transmitters 
on a net would have somewhat different char- 
acteristics, means were provided either to con- 
trol several actual transmitters or to simulate 
several equipments by small shifts in frequen- 
cies and any desired shift in power output. At 


310 


RCM IN THE EUROPEAN AND MEDITERRANEAN THEATERS 


the end of a transmission, a controlled signal 
on the record automatically selected the proper 
station to reply. 

Other work involving RCM weapons, but with 
a completely different purpose, was the use of 
Chaff loadedT in mortar shells to indicate to 
friendly radar sets the position of the front 
line. This development was initiated in ETO 
but was later transferred to development agen- 
cies in the United States. 

The only known example of active RCM car- 
ried on in support of ground forces is one in 
which the cooperation of the Air Forces was re- 
quested to jam the enemy tank communications 
by flying over the battlefield equipped with spe- 
cial jammers. Special aircraft of the Eighth Air 


Force were employed for this mission. Ameri- 
can-built ART-3 jammers were originally em- 
ployed but British sets of the Jostle were used 
in the last part of World War II. During the 
battle of the Ardennes, a number of tank jam- 
ming missions were flown. The characteristics 
of these f-m jamming signals were such that 
the German a-m tank equipment was fairly 
easily jammed, whereas the American tank sets 
operating in the same bands with well-designed 
f-m receivers could operate satisfactorily 
through very heavy jamming. During these op- 
erations, little interference was experienced by 
the American tanks, whereas evidence exists to 
indicate that German tanks underwent serious 
jamming. 


Chapter 15 

RCM IN THE PACIFIC THEATERS OF OPERATIONS 


‘51 INTRODUCTION 

T he keynote of the RCM program in the 
Pacific Theaters of Operations was that of 
investigation, as contrasted to the program in 
the Mediterranean and European Theaters of 
Operations. Offensive countermeasures were not 
employed until the early fall of 1944. At the 
start of World War II, Allied knowledge of 
Japanese radar was nonexistent, and, before a 
countermeasures program could be planned, a 
great deal had to be learned about the types of 
equipment and the operational tactics employed 
by the Japanese. 

‘5 2 the JAPANESE RADAR AND ITS 
OPERATIONAL IMPORTANCE 

It was not until August 1942 that it was posi- 
tively known that the Japanese had radar. At 
that time, in the invasion of Guadalcanal, a 
Japanese radar set was captured. This was a 
Mark I Model 1, intact. In the spring of 1943, 
searches conducted by Ferret I, in the Aleutians, 
confirmed the existence of two Mark I Model 1 
radars on Kiska. These two sets and a similar 
one at Wake Island had, however, been first dis- 
covered by aerial photography. Early in 1944, 
Ferrets in the Southwest Pacific Area [SWPA] 
confirmed the use of 75-mc, 100-mc, 150-mc, and 
200-mc early-warning [EW] radars in the 
region of the Admiralty Islands and Hollandia. 
Captured documents revealed that the SCR-268 
and the SCR-270, as well as the British gun- 
laying [GL] Mark II and searchlight control 
[SLC] had been compromised during the Jap- 
anese advance into the Philippines and down 
the Malay Peninsula. Thus it was relatively 
certain that by the end of 1943 the Japanese 
radar art was comparable to that of the Allies 
in 1941. 

Evidence of German- Japanese liaison existed, 
for example, in Japanese notebooks found at 
Hollandia, New Guinea, in which detailed sum- 
maries of the German Air Force radar jamming 
policy were given. It was certain that the Jap- 


anese knew, in August 1943, of the use of Win- 
dow by the RAF during the historic Hamburg 
raid in July 1943. Later information revealed 
that the enemy also knew the characteristics 
of the British ground-controlled interception 
[GCI], aircraft interception [AI], air-to-sur- 
face vessel [ASV], H2S, and, in addition, had 
at least a superficial knowledge of Allied identi- 
fication friend or foe [IFF] and tail warning 
receivers. Submarine searches in the Nanpo 
Shoto and Nansei Shoto chains and around the 
southern coast of the home islands of Japan 
revealed a well-developed radar net, although 
at that time it was impossible to judge the 
efficiency of their operation. In the summer of 
1944 the 20th Bomber Command searches in 
the China-Burma-India [CBI] Theater and 
over the island of Kyushu revealed the same 
types of EW radar that had been found in other 
Pacific areas, and analysis revealed very com- 
plete EW coverage over occupied China. Intel- 
ligence information indicated that the Japanese 
were working on 10-cm air-warning radar for 
both land-based and ship-based applications. In 
the spring of 1945, a number of intercepts of 
suspected Japanese 10-cm radar were made 
over the home islands of Japan and in the For- 
mosa area; however, in general, these radars 
were sporadically operated, and no widespread 
use of land-based 10-cm radar by the Japanese 
was ever confirmed. 

It was known that the Japanese had airborne 
radar of the ASV type, operating on 150 and 
200 me. The ASV, Air Mark VI, operating on 
150 me, was used extensively by the Japanese 
in attacks on U. S. naval units. The Ferrets 
operating over Formosa made a number of in- 
tercepts in the frequency range 500 to 520 me, 
which corresponded to that of Japanese air- 
borne radars described in captured documents. 
These were suspected of being a type of AI 
radar, possibly adapted from the German Lich- 
tenstein. Signals in the frequency range 1,000 
to 2,000 me were intermittently heard over the 
Japanese home islands and, in similar fashion, 
those around 1,100 me corresponded with the 


311 


312 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


information in captured Japanese documents. 
No definite evidence was ever obtained that 
these signals actually emanated from enemy 
aircraft or that they were used for the purpose 
of aircraft interceptions. 

The existence of ship-based radars had been 


had revealed that work was progressing on an 
adaptation of the German Wurzburg for ship- 
based operation, and several signals were inter- 
cepted around 650 me during the shelling of the 
Mindoro beachhead by a Japanese task force. 
A CincPac report mentioned the interception 



Figure 1. Aerial photograph showing dual installation of Japanese early-warning, Mark I Model 1 
type radar immediately behind the main camp area at Kiska. Note the near miss of one bomb crater. 


revealed in captured documents and numerous 
intercepts were made during engagements with 
enemy naval units. These radars, operating on 
150 and 200 me, were used for air-warning 
purposes. There were also indications that the 
Mark IV Model 3 had been adapted for ship- 
board searchlight control. Captured documents 


and jamming of a signal at 606 me near Zam- 
boanga in the summer of 1945. It was also 
known that the Japanese had installed the 
Mark II Model 2, 10-cm surface-search radar, 
on ships; and its presence was first noted by 
interference on the indicators of 10-cm U. S. 
naval radars. Its characteristics were later 



THE JAPANESE RADAR AND ITS OPERATIONAL IMPORTANCE 


313 


verified by signal intercept and analysis. An 
adaptation of the Mark II Model 2 for surface 
fire control appeared but never proved effective. 
Direction-finding [DF] work indicated that a 
70-mc radar, having characteristics similar to 
the Mark CHI land-based radar, was being used 
on picket boats. Intercepts also revealed that 
the 28-mc SE radar and the Mark III doppler 
radar were being used on picket boats to a very 
limited extent. A lightweight radar was found 
which operated on 375 me and which was to 
be used on suicide assault boats for directing 
attacks at night. 

Captured documents had revealed the exist- 
ence of Japanese GL and SLC radar, copied for 
the most part from American and British sets 
captured in the early days of World War II. An 
SLC radar, the Mark IV Model 3, was captured 
on Saipan in June 1944, and a Mark IV Model 1 
was captured on Peleliu in September 1944. In 
October 1944, 5th and 13th Air Force units had 
gathered sufficient evidence to establish the 
existence of 200-mc radar in the Balikpapan 
area, having characteristics which indicated 
that it could be used for gun laying. Units of 
the 5th Air Force also intercepted 200-mc GL 
signals in the Clark Field area on Luzon and 
75-mc GL signals on Takao, Formosa. In Feb- 
ruary and March 1945, a large number of inter- 
cepts at 75 and 200 me were associated with 
flak and searchlight activity by 21st Bomber 
Command units over the home islands of Japan. 
No definite intercept of a signal having Wurz- 
burg characteristics was ever made over land. 
In only one instance was a 10-cm intercept ever 
associated with flak and this was probably pure 
coincidence. 

Thus, the Japanese were seen to have crude, 
but effective, EW radars in quantity. The EW 
coverage in the Southwest Pacific Area was far 
from complete because of the relatively few 
radars available and the large distances be- 
tween islands ; coverage gaps were further aug- 
mented by U. S. efforts to destroy particular 
sites. In the CBI Theater, enemy EW radar 
coverage was extensive, and, since the B-29 
raids across China had to follow a prescribed 
course at high altitude, it was considered im- 
possible to avoid the EW net. In the Western 
Pacific, the EW net in the Nansei and Nanpo 


Shoto chains was elaborate but susceptible to 
deception and destruction. Early-warning cov- 
erage for the southern coast of Japan was ex- 
tremely good and the concentration of radars 
and the diversification of frequency made de- 
ception or destruction of individual installations 
unprofitable. 

By the end of 1944, Japanese airborne radar 
reached a technical level comparable to that of 
the Allies in 1941. It never constituted a prob- 
lem to the U. S. Air Forces. It did, however, 
help the Japanese in shadowing U. S. Fleet 
movements and was often used to guide Kami- 
kaze attacks; for both of these reasons it was 
a definite menace to naval operations. The few 
intercepts at 500 me and 1,100 me indicate that 
the Japanese were on the road to better air- 
borne radars, particularly AI, and their use 
might have developed into a serious problem 
for the Air Forces. 

Ship-based radars were, for the most part, 
dual-purpose sets, comprising the design char- 
acter of both surface-search and fire-control 
equipment. By changing the pulse width and 
repetition frequency, the enemy attempted to 
transform his radar magically from one pur- 
pose to another. The result was a mediocre 
search set and a very poor, almost useless, fire- 
control system. In spite of this fact, a few cases 
are on record of the enemy's ineffective attempt 
to utilize ship-borne fire-control radar. A 650- 
mc set may have had possibilities for surface 
fire control, but it never passed the experi- 
mental stage. 

Japanese land-based fire-control and search- 
light-control radars, admittedly four years be- 
hind Allied developments, were instrumental in 
permitting the Japanese to shoot down our air- 
craft under unseen conditions. As such, they 
constituted a serious Air Force problem. 

The Japanese themselves understood that 
their radar was inferior to that of the Allies 
and sought to present flimsy excuses to their 
people. For example, an article in the January 
1944 issue of Manichi Shimbun said: “The 
point where our electrical weapons are sur- 
passed is not in design but in manufacturing 
technique . . . the glass porcelain, filling mate- 
rials, filament, etc., are of lower quality and 
the life of the valve is short." 


314 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


15 3 THEATER ORGANIZATION 

For the purposes of this report, the Pacific 
Theaters of Operations are subdivided into the 
following areas: The Northern Pacific; the 
Southwest Pacific ; the China-Burma-India ; the 
Central and Western Pacific. In the Northern 
Pacific Area, radar countermeasures [RCM] 
activities were carried on by the Eleventh Army 
Air Force, Army Ground Force units, and naval 
air and sea units of the Eleventh Fleet. The 
Fifth and Thirteenth Army Air Forces, Army 
Ground Force units, and the Navy Seventh 
Fleet were engaged in RCM operations in the 
Southwest Pacific Area. The RAAF also carried 
on a small-scale RCM effort in the Southwest 
Pacific Area, but their activities will not be 
considered here. In the CBI Theater, the Twen- 
tieth Bomber Command of the Twentieth Air 
Force, the Tenth Air Force, and the Fourteenth 
Air Force were engaged in the investigational 
phases of the RCM program. In the Central and 
Western Pacific Areas, the Seventh Army Air 
Force, the Twenty-first Bomber Command of 
the Twentieth Air Force, and units of the 
Third and Fifth Fleets were all engaged in 
RCM activities. The RCM organization within 
each theater is discussed briefly in later sec- 
tions. 


15 4 U. S. CIVILIAN AID TO THE 
ARMED FORCES 

Twenty civilian technical observers or scien- 
tific consultants were supplied to the Pacific 
Theaters of Operations by the Radio Research 
Laboratory [RRL] of Harvard University. In 
the Pacific, there was never a completely civil- 
ian laboratory, similar to the American-British 
Laboratory of NDRC Division 15, and, in gen- 
eral, civilian personnel were assigned directly 
to the air force or theater headquarters which 
requested their services. A civilian technical 
observer accompanied the Beaver I mission to 
the Aleutian area and advised in the technical 
and operational phases of its activities. Ferrets 
VII and VIII were accompanied to the South- 
west Pacific Theater by two technical observers 
and, throughout the period of operation of these 


Ferrets, at least one civilian was assigned to 
the organization controlling their operation. 
Section 22 of General Headquarters, Southwest 
Pacific Area, at one time had as many as six 
scientific consultants attached to its RCM staff ; 
the majority of these were assigned to the Fifth 
and Thireenth Air Forces to aid in their instal- 
lation and operational program. The 20th 
Bomber Command (the first operational unit of 
the global 20th Air Force) had assigned to it 
two technical observers, who reached the CBI 
Theater before the Twentieth Bomber Com- 
mand began operations. One of these two was 
subsequently assigned to the Fourteenth Air 
Force and aided in the outfitting of the interim 
Ferret for that air force. Technical observers 
remained on duty with the Twentieth Bomber 
Command until it moved to the Marianas. At 
various times, civilian scientific consultants 
were attached to Headquarters, United States 
Army Forces, Pacific Ocean Area, Hawaii, 
where they aided units of the Army Ground 
Forces, Army Air Forces, and Pacific Fleet in 
the Hawaiian area. A civilian technical observer 
was attached to the Twenty-first Bomber Com- 
mand of the Twentieth Air Force and accom- 
panied it overseas to the Marianas ; he advised 
on its operational and installation program 
throughout the nine months of its existence. 


15.5 naval radar COUNTERMEASURES 
® ^ Organization 

The Naval RCM Problem in the Pacific 

In the Atlantic and European Theaters, the Navy’s 
radar countermeasures problems were concerned with 
two very specific situations: convoying; and supporting 
amphibious landings. Information concerning German 
radar developments was plentiful and definite, due to 
proximity and wide-spread German use, and, therefore, 
the requirements for radar countermeasures were 
equally definite: (1) convoys had to be provided with 
a radar-countermeasures team capable of intercepting 
and locating enemy U-boat radars when used; (2) dur- 
ing amphibious landings radar-countermeasures teams 
had to be provided capable of jamming enemy coast- 
watcher and gun-laying radars for the protection of 
amphibious forces during the actual landing operations. 
In this latter case all available radar counter-measures 
material and personnel could be concentrated for the 
landing involved and then shifted to cover the next 


NAVAL RADAR COUNTERMEASURES 


315 


operation. Because of the above considerations, plus 
the fact that much of the necessary preliminary inter- 
cept and intelligence information was already provided 
by the Army and the British, a few small Navy radar- 
countermeasures expert teams were found most efficient 
for operation in the Atlantic and European Theaters. 

In the Pacific an entirely different state of affairs 
existed and required radically different approaches and 
solutions. In the first place, as late as the middle of 
1942, practically nothing was known about Japanese 
radar developments. This was due to a second factor — 
the tremendous distances involved in the Pacific. In 
fact, it was not until after the Marines had captured 
an early model Japanese radar on Guadalcanal and when 
it became possible to project radar intercept equipment 
mainly by plane and submarine into Japanese controlled 
areas, that sufficient information about Japanese radars 
became available to permit initial planning of jamming 
equipment. Another factor was the difference in the 
state of radar development in Japan and Germany. The 
Germans were well advanced both in quality and quan- 
tity of equipment over the Japanese which at once was 
a curse and a blessing from the point of view of Pacific 
radar countermeasures. The legitimate needs of the 
European Theater to counter an immediate enemy radar 
threat left few personnel and little equipment for the 
Pacific. On the other hand, until 1943, there was little 
need for more than “watchful waiting” in radar 
countermeasures in the Pacific. 

However, by the fall of 1943, the Japanese had a 
rather extensive radar net in operation and the value 
of the exploratory work being performed by the few 
radar countermeasures teams became increasingly ap- 
parent. By the summer of 1944, this radar net had 
reached the point where it constituted a genuine threat 
to our forces; it was immediately obvious that a change 
in concept was in order. Pacific operations spread over 
a vast expanse of ocean and islands and one might 
encounter enemy radars — shore, ship, submarine and 
airborne — at any point and any time in this immense 
area. Also, one “D-Day” followed closely on the heels 
of another; it became impossible to transport radar 
countermeasures material and personnel rapidly enough 
to fill the needs, and there was no guarantee of having 
them when and where they were needed. Even when 
offensive operations were not in progress, there was 
never enough information on Japanese radars — types, 
locations, and uses. To fill these requirements, radar 
countermeasures was taken out of the “special team” 
category and integrated with the fleet radar and CIC 
programs. As more and more equipment became avail- 
able it was spread throughout the surface fleet, sub- 
marines, and air force from the Aleutians to the 
Marshalls, from Pearl Harbor to Okinawa, until at 
the end of the war, radar countermeasures had become 
a fleet-wide proposition taking its place alongside and 
supplementing radar — the weapon it served to deny to 
the Japanese and whose every use on their part worked 
only to their own detriment. In this status it is today, 
and will remain — a full-fledged weapon of the fleet. 


Inception of United States RCM Effort 

/ 

Shortly before December 7, 1941, it became apparent 
to several of the electronics officers in the Navy Depart- 
ment in Washington, that our rapidly expanding devel- 
opment and application of electronics devices to warfare 
would require an aggressive program of countering 
similar devices which would be used by our enemies. 
Within a few days after the Pearl Harbor attack, a 
meeting was called at MIT at the suggestion of one 
of the Navy bureaus to enable Service representatives 
to discuss the general problem of countermeasures 
equipments, techniques, etc. At a subsequent conference 
held in the Navy Department, it was decided by NDRC 
that a new laboratory should be established to handle 
this work rather than overloading the already over- 
worked staff at the Radiation Laboratory. 

Out of these conferences grew the Harvard Univer- 
sity contract for the establishment of the Radio Re- 
search Laboratory. Some countermeasures work had 
been done, however, by NRL prior to the establishment 
of the NDRC facility and the work at NRL expanded 
during the war and supplemented the efforts in this 
field put forth by NDRC. 

RCM IN THE Navy Department, 

Washington, D. C. 

The Navy Department Countermeasures activities 
were centralized by a countermeasures group estab- 
lished under the Director of Naval Communications, 
and the establishment of the Countermeasures Section 
in the Radio Division of the Bureau of Ships and a 
Countermeasures Desk in the Radio and Electrical 
Section in BuAer provided focal points in the -two 
bureaus for the coordination of countermeasures activi- 
ties and the active development of countermeasures 
equipments. The unusual nature of the electronics 
countermeasures problem made it essential to maintain 
extremely close liaison between the development labo- 
ratories, the tactical organizations in the theaters which 
use electronic equipments, and intelligence and other 
information groups which provide information concern- 
ing enemy electronic systems in use or projected which 
must be countered. There was also a need for very 
close coordination between the branches of the Services 
and the development laboratories concerned with the 
problem. As a result of this need, the Joint Counter- 
measures Committee was established by the Joint Com- 
munications Board of the Joint Chiefs of Staff during 
the summer of 1942. The representative of the Director 
of Naval Communications was elected chairman of the 
committee. This committee functioned very effectively 
to maintain coordination and an aggressive, cooperative 
spirit among the several interested branches of the 
Army and Navy and with the NDRC research labora- 
tories. 

RCM IN THE Fleet 

Originally countermeasures officers and men with 
training in radar countermeasures, communication 


316 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


countermeasures, and anti-jamming methods arrived in 
the Pacific Theater grouped into teams. It was found 
expedient, however, to assign the officers and men either 
individually, or in smaller groups later known as 
^‘Functional Components.” By 1 September 1944, the 
Navy personnel situation was as follows: a number of 
Functional Components were formed under ComDesPac, 
ComSubPac, ComNorPac, and COTCPac and employed 
to man RCM equipment during fleet operations and for 
training purposes between operations. In addition, fif- 
teen graduates of the Applied Communications Course 
at the Post Graduate School, USNA, with additional 
countermeasures training had been assigned to key 


School, USNA) and at the Pacific Fleet Radar Center. 
Personnel aboard ships without early availability at 
Pearl Harbor can receive RCM instruction from forward 
area training teams and groups. It should be noted that 
specialized RCM personnel as such are not ordered to 
individual ships for permanent duty; their radar and 
CIC personnel should take advantage of one of the 
above-mentioned training courses depending upon the 
nature of the ship’s availability. 

The formal training of countermeasures per- 
sonnel first received attention in December 1942 
when Op-20-S-2 in VCNO formulated a training 



Figure 2. RCM antenna installation on PB4Y-2 long-range naval patrol bomber. 


Navy staffs to advance the fleet countermeasures pro- 
gram in its earlier stages. 

In each of these “key Navy staffs” (CincPac, 
ComNorPac, ComSouWesPac, Com Eleventh 
Fleet, Com Seventh Fleet, Com Third Fleet, and 
Com Fifth Fleet), RCM was destined to play a 
major role. 

By the beginning of 1945, when RCM was 
put on a fleet-wide basis, a new personnel plan 
was necessary. As evidenced by the paragraph 
below, countermeasures transcended, at that 
time, the role of an electronic specialty : 

Although GMCM, CCM, and a limited number of RCM 
assignments will be handled by specialists, shipboard 
RCM duties will be performed by our ships’ radar and 
CIC personnel. Training in RCM is now given to radar 
operators, radio technicians, CIC watch officers, radar 
material officers both in mainland schools (including the 
course in Applied Communications, Post Graduate 


plan and queried staff commanders such as 
CincPac, CincLant, Com Third Fleet, and Com 
Seventh Fleet about the desirability of attach- 
ing officers with such RCM training to their 
staffs. General concurrence was received and 
the first two groups of officers were assembled 
for training in January 1943; after a seven 
weeks’ course at the Special Projects School, 
Anacostia, Maryland, they departed for duty. 
(One of the 7 weeks was spent at the Radio 
Research Laboratory, Harvard University.) 
Slightly later, a special projects school for air 
was set up in conjunction with BuAer, Op-33, 
and Op-31. In addition to the above Stateside 
training facilities, several RCM schools were 
established in the Pacific. For example, at Pearl 
Harbor there was the Fleet Radar Center, with 
auxiliary groups in ComDesPac, ComSubPac, 



NAVAL RADAR COUNTERMEASURES 


317 


and ComAirPac. At least twice a week these 
training activities sponsored the use of elec- 
tronic jammers and various forms of Window 
against Hawaiian radar defenses. In the cri- 
tiques which followed each exercise there was 
an opportunity to evaluate the tactical merit 
of numerous RCM plans. In addition, valuable 
lessons were learned by the operators of both 
the radar and the countermeasures equipment. 

To supplement the RCM education of staff 
and operating personnel, two books had been 
published by March 1943, the first known as 
Radio and Radar Countermeasures, CSP 1765 
(a), and the second. Black Magic, CSP 1772 
(A). Later on, fleet education was supple- 
mented by films prepared in the Bureaus, Naval 
Research Laboratory [NRL], RRL, and the 
Joint New Weapons Committee [JNW]. In 
addition, RAD-7, Operators Countermeasures 
Marnuil, and RAD-12, The Airborne Counter- 
measures Operators Mamuil, were prepared as 
textbooks under the direction of COMINCH. 

In retrospect, the Navy installation program 
is seen to fall into three categories : stopgap, in- 
terim, and ultimate. The first category involved 
prototype equipment installed in surface ves- 
sels by a specialized team after the vessel was 
under way toward an enemy objective. Such a 
procedure was followed from August 1943 until 
the spring of 1944. At that time, interim instal- 
lations of production-line intercept receivers 
and 1-f jamming transmitters were begun 
mostly on the smaller vessels. Ultimate installa- 
tions with the elaborate RCM equipment allow- 
ances started in the first part of 1945. 

The tactical plans, policies, and doctrines 
governing the use of radar, radio, and guided 
missile countermeasures in the U. S. Navy were 
consolidated for the first time at the end of 
1944 in Cent Com Two, Annex B ; as the use of 
RCM equipment expanded, this document was 
periodically revised and supplemented. Similar 
material, revised to April 1945, is contained in 
P AC-70 (B), Radio and Radar Countermeas- 
ures and Deception. 

Investigation 

The foremost problem in naval countermeas- 
ures operations was one of securing intelligence 


on enemy radar. Since this problem continued 
throughout the length ot\ World War II, the 
sources of such intelligence were carefully de- 
veloped to include 

1. Interference on U. S. radar. 

2. Use of intercept receivers, analyzers, and 
DF antennas. 

3. Captured equipment. 

4. Captured documents. 

5. Prisoners of war. 

6. Agents. 

7. Aerial photographs. 

8. Periscope inspection. 

9. Radio interception and analysis. 

10. Deductions from the analysis of combat 
operations. 

Each of these various means was, at one time 
or another, used by U. S. naval forces to deter- 
mine the quality, quantity, disposition, and op- 
erational usage of Japanese radar. For a de- 
tailed account of the information gained, one 
may consult two publications, Japanese Shore- 
Based Radar Locations and Japanese Radio and 
Radar Equipment, which were prepared by the 
Radar Countermeasures Section of the Com- 
mander-in-Chief, U. S. Naval Forces in the 
Pacific. It is interesting to note that by October 
1944, when Japanese airborne radar offered the 
first serious threat to U. S. naval operations, 
sufficient information was available to permit 
the successful use of offensive radar counter- 
measures. 

Perhaps the first contact with Japanese radar 
came on November 6, 1941, before the outbreak 
of hostilities. The USS Chester, proceeding in 
slow convoy with two Army transports near the 
Marianas, made radar contact with an uniden- 
tified vessel. Interference was noted on the A 
scope of the Chester's newly installed CXAM, 
a 200-mc search set. In the absence of other 
radar, the interfering radar signal, which 
appeared to be variable in frequency, pulse 
length, and repetition rate, was believed to orig- 
inate on the unknown vessel, tentatively identi- 
fied as a Japanese destroyer. Needless to say, 
such information was inconclusive and offered 
no concrete basis for the future planning of 
countermeasures equipment. 

By December 1941, an American intercept 
receiver known as the P-540 had been success- 


318 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


fully flown over Germany; the British had 
ordered approximately a hundred, and on 
December 22, 1941, it was pointed out that such 
intercept gear was a prime necessity for U. S. 
investigations in the Pacific. The Naval Re- 
search Laboratory began work on a crystal or 
diode detector-type receiver, later to be known 
as the XARD, while the Radio Research Lab- 
oratory of Division 15, NDRC, undertook to im- 
prove the design and increase the frequency 
range of the P-540, a superheterodyne receiver 
with plug-in tuning units. 

As search receiver development continued in 
the United States, far-ranging Navy sub- 
marines with 114-mc SD radars encountered 
numerous cases of interference. The first of 
these reports came in December 1942, off the 
atoll of Truk; such information correlated rea- 
sonably well with the measured characteristics 
of an enemy Mark I Model 1 search radar cap- 
tured at Guadalcanal. 

Thus, the first year of the Pacific war netted 
only a small amount of information on Japanese 
radar. It was firmly concluded that the Japa- 
nese were cognizant of radar techniques and had 
developed EW-type radar prior to the outbreak 
of hostilities. Such sets as the Mark I Model 1 
were known to operate from 92 to 108 me for 
purposes of land-based air search. Japanese 
ship-borne and aircraft radars were suspected 
but not proved. No radar jamming or deception 
had been tried operationally by either side. By 
comparison, the investigational phases for Jap- 
anese communications had progressed tre- 
mendously because conventional 1-f, ground- 
based receivers could monitor distant trans- 
missions. 

Search receiver development, progressing at 
high priority in U. S. laboratories, had reached 
the stage of prototype equipment for the lower- 
frequency ranges, 40 to 300 me, by January 
1943. A sample quantity of receivers, XARD 
and ARC-1 (the outgrowth of P-540), were 
prepared for installation in aircraft, surface 
vessels, and submarines. The Army Ferret I, 
destined for radar reconnaissance of the Aleu- 
tians, received one of each equipment, as did a 
Navy PBY operated by Section 22, General 
Headquarters, Southwest Pacific; the balance, 
no more than ten, went aboard naval vessels. 


By March 1943, two more Mark I Model 1 
radars had been captured in the invasion of 
Attu. Ferret Ps radar reconnaissance of the 
Aleutians had been completed and the dual 
radar installation above the main camp area 
at Kiska Harbor was sufficiently well known 
that offensive RCM operations could be 
planned. The Beaver I mission, organized to 
counter specifically these two sets, enjoyed the 
assistance of one Navy officer and four Navy 
enlisted men, in addition to RCM personnel de- 
tached from the staff of ComNorPac. 

In the south and southwest Pacific, by the 
use of prototype intercept receivers, a total of 
34 different Japanese radars had been reported 
by June 1943. These radars, according to inter- 
cept information, extended from 100 to 740 me, 
with noticeable concentrations at 100, 150, 200, 
300, and 700 me. Evaluation of these first re- 
ports was a tedious and uncertain job, because 
the ARC-1 offered many spurious responses and 
knowledge of friendly radar characteristics was 
not widely spread within our own forces. 

Up to this time, radar intelligence had come 
primarily from captured equipment, captured 
documents, and aerial photographs. Here for 
the first time, then, we find a sizable increase 
in our knowledge of the enemy’s radar defense 
by the use of flight intercepts. Ship-borne re- 
ceivers were to produce worth-while intercepts 
a short time later in August 1943. 

In summarizing naval intercept operations 
up to the end of 1943, it is seen that captured 
documents, captured equipment, aerial photo- 
graphs, and airborne and ship-borne intercepts 
were the principal sources of U. S. knowledge 
of Japanese radar. At year’s end, 14 land-based, 
EW search radars had been definitely located 
in the Southwest Pacific Area. The number of 
different enemy radar intercepts was approach- 
ing one hundred. The existence of Japanese 
ship-borne or airborne radar was still not defi- 
nitely proved, though documents had been 
found referring to 200-mc ship-borne equip- 
ment of the EW type. No offensive counter- 
measures had been employed by U. S. naval 
forces. 

Investigation by Naval Aircraft 

Investigation and intercept to determine the 


NAVAL RADAR COUNTERMEASURES 


319 


quality, quantity, disposition, and operational 
usage of Japanese radar was undertaken by 
tender-based, land-based, and carrier aircraft. 
The earliest operations of this kind utilized 
land-based aircraft with prototype search 
equipment. As mentioned in the above para- 
graphs, a B-24, known as Ferret I, and a Navy 
PBY started operations in the early spring of 
1943, in the Aleutian and Southwest Pacific 



Figure 3. Typical PB4Y-2 RCM installation. 
Reading from left to right are : top shelf — 

1 AN/ APT-1, 1 AN/APA-10; middle shelf — 

1 AN/APA-11, 1 AN/APA-17; bottom shelf — 

1 AN/ APT-5, 1 AN/ APR-1. 

Areas, respectively. Although both of these air- 
craft were under the immediate operational 
control of the Army, they drew heavily on pro- 
totype equipment developed under Navy spon- 
sorship. Although the supply of intercept re- 
ceivers was still in short quantity, in September 
1943 

planes flying under Admiral Halsey’s command in the 
South Pacific commenced regular search operations to 
intercept, locate, photograph, and bomb out Japanese 
radar installations. ... In addition to the regular 


searches, [these] planes were kept continuously on 
station night and day in and above the upper Solomons 
to detect Japanese shipping. Any such ships using their 
radars were spotted by the radio-countermeasures 
equipment in these planes and reports made of their 
presence thereby. In addition, this equipment was used 
to tell if the planes themselves had been detected by 
the Japanese radars; if such were the case, position was 
quickly changed, since planes and trained flight crews 
were at a premium in the “shoestring” days of 1943.852 
In November of 1943, radar-countermeasures- 
equipped “Black Cats” — Navy night-flying PBY’s — 
commenced similar operations under the Southwest 
Pacific Area command and, together with Army “Fer- 
rets,” located, studied, and bombed Japanese radar in 
that area.852 

By the beginning of 1944, the broad strategy 
for future Pacific operations had been crystal- 
lized. As an adjunct to the numerous landings 
which were planned. United States carrier 
forces were asked to carry out raids deep in 
enemy waters. For example. Central Pacific 
carrier forces had selected highly touted Truk 
in the Carolines as their first target. Target 
data were required, since no previous recon- 
naissance of this enemy base had been con- 
ducted. It was decided that aerial photographs 
might be obtained by Marine photo-reconnais- 
sance planes flying from advance bases. To as- 
sist the protection of these photo-reconnais- 
sance aircraft, as well as to obtain radar recon- 
naissance information for later uses, an RCM 
investigation was scheduled as the first move 
in the operation. The first flight, then, was made 
by land-based naval patrol bombers which took 
off from Munda and refueled at Bougainville. 

With belly tanks so full of fuel for the long hop to Truk 
and back that the bomb bay doors couldn’t be closed for 
300 miles, they flew over and around the “vaunted and 
impregnable fortress” charting the coverage of the 
various Japanese radars. Based on the information 
brought back from this radar-countermeasures flight, 
the Marine photo-reconnaissance planes approached 
Truk in a blind sector of the Japanese radars, took 
their pictures and left before the unalerted Japanese 
were fully aware that the planes had been overhead. 

The preliminary radar investigation of Truk 
was put to such excellent use by the Marine air- 
craft that additional investigations were 
ordered for later use by carrier and other 
forces. The task was assigned to VPB 116, a 



320 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


squadron of PB4Y aircraft then operating from 
Eniwetok. A report on these missions is quoted 
here in the words of Commander Donald G. 
Gumz. 

We did use it (RCM) when we got forward, to con- 
duct a radar survey of enemy radar facilities in Truk. 
ComAirForwardArea at the time asked us to locate 
enemy radar equipment on Truk and attempt to pin- 
point it. Unfortunately, the Japanese transmitters they 
were using there most effectively were between 98 and 
105 me, I believe, and it was very difficult for us to get 
any kind of bearing with our equipment, on a trans- 
mitter on that frequency. Consequently, we had to think 
of something new. The plan required about six night 
sorties up in that area with the three RCM planes 
searching for holes in their screen at varying altitudes. 
We ran three concentric circles around Truk lagoon, 
one at around 2,000 feet altitude, and staying just out- 
side their range. We’d come in and they would pick us 
up, and then we’d drop back out again. Using our 
George gear, to keep our position accurately pointed, 
we got a circle at 2,000 feet. It had holes in it where 
we could approach closer. Then we went in at a thou- 
sand feet and did the same thing for a thousand foot 
circle. And then we closed in to a 500 foot altitude vs. 
intercept circle. We noted that consistently there were 
spots opposite certain islands and projections that would 
permit us to close considerably inside that outer circle 
at that altitude, and they all pointed towards a plateau 
on Moen. So one morning we went inside the lagoon, 
primarily on a shipping strike at low level and saw no 
shipping but did pick up some interesting information. 
As soon as we got inside the shadow of Moen, the 
98-105 me radars that had been following us all the 
time lost us. Once inside the reef, it turned out that 
they couldn’t depress the antenna and follow us, but 
we did pick up a 300 me which was a very strange 
frequency to us then, and another odd frequency, 
198 me, I believe, picked us up immediately and started 
following us again. Well, naturally we expected a rather 
hot reception knowing that we had been on their screen 
for some time (15 minutes before we crossed the reef 
line), and we were always very much amazed that there 
were no fighters airborne when we got in. It wasn’t 
until we had completely circumnavigated the lagoon 
and followed the shore line around Moen within 20 and 
40 mm range and were on our way out, that they 
launched fighters. It was something that I have never 
been able to reconcile with the fact that their radar 
intercept of an approaching single airplane was excel- 
lent enough to pick you up at 50 feet altitude some 
30 miles from the reef. Incidentally, their operators 
were very good. We could shake our own in the Oahu 
area, but we could never shake them, except by getting 
out of range. Those operations were the most interesting 
that we conducted out of Eniwetok at the time. 

As a result of such searches, the succeeding 
carrier air strikes on Truk were planned in a 


way that assured the least reaction by Japanese 
aircraft and the greatest safety to U. S. carrier 
forces. 

In August 1944, prior to the first Philippine 
operation, plans were laid for radar reconnais- 
sance of Leyte Gulf, Manila, and other Philip- 
pine areas by a small number of TBM's. These 
same aircraft were also to be used for an in- 
vestigation of the Palau group. Unfortunately, 
these plans were never carried out because sev- 
eral of the TBM’s were destroyed before seeing 
action. 

At approximately this same time, the instal- 
lation of RCM equipment in naval aircraft was 
proceeding according to an interim program. 
A standard allowance of RCM equipment for 
the planes of each squadron of land-based naval 
aircraft had been established; for carrier air- 
craft, installations were made on the basis of 
the demands of a specific operation. Thus, by 
the end of August 1944, 18 squadrons of land- 
based naval patrol aircraft were operating in 
the Pacific, and in 13 of these squadrons, instal- 
lations of the following equipment had been 
completed : 

1 AN/APR-1, 

1 AN/APA-6, 

1 “Snooper’" DF antenna, 

1 Jamming transmitter (AN/APT-1, 
AN/APT-3, or AN/APQ-2). 

In addition to these, installations of M-2300 
(later known as AN/APA-17) were made in 
one plane each of squadrons VPB 102, 116, and 
117. One AN/APR-5 was installed in one plane 
each of squadrons VPB 146 and 150. 

As operations continued, airborne intercepts 
were of greater and greater value; as early 
as the fall of 1943, long-range planners in the 
Bureau of Aeronautics were moved to include 
a formidable RCM installation in the Navy’s 
new land-based search aircraft, the PB4Y-2. 
By mid-1944, search operations had so con- 
firmed their conclusions that additional RCM 
equipment was authorized for the PB4Y-2. This 
aircraft, similar to a B-24, though modified by 
adding 7 ft to the fuselage and utilizing a single 
tail, was to be equipped with 
1 AN/APR-1, 

1 AN/APR-2, 

1 AN/APR-5AY, 


NAVAL RADAR COUNTERMEASURES 


321 


1 AN/ARR-5, 

1 AN/ARR-7, 

1 AN/APA-6A or AN/APA-11, 

1 AN/APA-17, 

1 AN/APA-24, 

1 AN/APA-10, 

1 AN/APT-1, 

1 AN/APQ-2, 

1 AN/APT-5. 

All of the above equipment was not intended 
for use at the same time. Standard mounting 
racks allowed for the interchange of intercept, 
analyzing, and jamming equipment depending 
on the nature of the mission. 

Carrier aircraft, following suit in October- 
November of 1944, adopted a similar ultimate 
installation plan with equipment allowances of 
5 AN/APR-1, 

5 AN/APA-6, 

5 AN/APT-1, 

5 AN/APQ-2, 

5 AM-14/APT, 

5 AM-18/APT, 

2 AN/APR-5AY, 

2 AN/APR-2, 

2 AN/APA-10, 

2 AN/APA-23. 

This equipment was placed aboard CV’s and 
CVL’s to permit RCM installations in five 
TBM’s or TBF"s per carrier. 

Each squadron of multiengined land-based 
naval aircraft (other than PB4Y-2’s) was au- 
thorized to equip three planes with the follow- 
ing RCM equipment: 

1 AN/APR-1, 

1 AN/APA-6 or AN/APA-11, 

1 "‘Snooper” direction-finding antenna, 

1 AN/APA-17, 

1 AN/APA-23, 

1 AN/APQ-2. 

The tactical doctrine controlling the use of 
this large quantity of equipment was formalized 
in Cent. Com. Two, Annex B, and later PAC-70 
(B) , at the same time that the ultimate installa- 
tion program got under way. With regard to the 
investigational phase of radar countermeas- 
ures operations, a generalized plan such as the 
following was adopted. 

1. As many carrier aircraft as practicable 
should be furnished with RCM intercept equip- 


ment and should accompany the first strike on 
any specific target area or on a large task force 
to determine the extent and effectiveness of 
enemy radar activities and to spot any previ- 
ously unreported enemy radar frequencies. Sub- 
sequent strikes should be accompanied by at 
least two RCM-equipped planes to insure that 
no new radars are placed in operation on dif- 
ferent frequencies. This RCM intercept infor- 
mation should be used to determine the length 
of Window to be dropped and the settings to 
which jammers should be pretuned. 

2. Shore- or tender-based air squadrons 
should maintain a continual RCM survey of 
enemy objectives. The fleet commanders may 
order detailed additional searches of any spe- 
cific enemy location they feel warrants such 
treatment. 

In addition to the above, shore-based air 
squadrons should make maximum use of their 
RCM intercept equipment for evasive tactics 
(flying around or under radar beams or coming 
down a null) and for homing purposes, to per- 
mit bombing and strafing of enemy radar loca- 
tions, and to obtain all possible information 
concerning enemy electronics to guide research 
and development agencies. In so far as prac- 
ticable, all bombing and search missions should 
include at least one RCM-equipped plane. 

Thus, by the beginning of 1945, with the ulti- 
mate installation program proceeding at a rapid 
rate and the fleet-wide adoption of Cent. Com. 
Two, Annex B, as a consistent policy, doctrine, 
and plan for the use of RCM, airborne radar 
investigations reached a climax at the time 
United States forces were operating most 
closely to the heavily defended shores of the 
enemy home islands. Shore-based search air- 
craft continued to contribute to our knowledge 
of enemy radar by performing the task which 
they pioneered. Carrier-based air intercept op- 
erations followed suit on a somewhat smaller 
scale. In particular, night carrier air operations 
were quick to realize the benefit of airborne in- 
tercepts. For example, the RCM officer of Night 
Carrier Air Group 90, based on the USS Enter- 
prise, made this evaluation of airborne inter- 
cepts at the conclusion of operations against 
enemy targets on Kyushu and the Inland Sea, 
March 18-20, 1945. 


322 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


It is believed that some emphasis should be made on 
“Ferret” flights. It is highly necessary to detect new 
enemy frequencies; to observe operating techniques; to 
pin-point stations. Sometimes this work can be done 
during regular scheduled flights (especially search mis- 
sions) without interfering with the primary mission of 
the aircraft. This was done by Air Group 90 in the 
South China Sea and on Heckler missions around 
Kyushu and the Inland Sea of Japan. 

The nature of some flights, such as the strike mis- 
sions in the Bonins, make it hard to do much intercept 
work. There the flight to the objective was of short 
duration. The aircraft would orbit at a designated 
position before making individual runs on the target. 
Then evasive tactics were used while getting away from 
the target, and proceeding to a rendezvous point more 
orbiting would be done. The operator, as a rule, would 
lose track of his location and therefore very few good 
fixes were obtained. It is believed that the primary 
purpose of RCM personnel and equipment on strike mis- 
sions should be to give the aircraft as much protection 
against FC/SLC radar and radar-equipped enemy air- 
craft as possible . . . Therefore, if strike missions are 
being sent out and RCM reconnaissance is needed, spe- 
cial flights should be made, if possible. In addition, 
when in enemy waters, a good RCM intercept watch 
can be made while on a routine anti-submarine patrol. 
It furnishes an excellent chance for an operator to gain 
experience and also makes valuable intercepts. 

In the succeeding months, intercepts by U. S. 
naval aircraft contributed to the effectiveness 
of each amphibious operation. A detailed ac- 
count of these later operations, given in the 
subsections entitled “Aircraft^^ under Sections 
15.5.3 and 15.5.4, reveals the extent to which 
U. S. naval forces relied upon the use of air- 
borne intercepts. In summary, it will be noted 
that naval airborne search equipment was used 
for the following purposes. 

1. To intercept and identify the different 
types of enemy radar. 

2. To determine the location of enemy air- 
borne, ship-borne, or shore-based radar by the 
use of DF antennas. 

3. To investigate the coverage of a given 
enemy radar site and to obtain information 
necessary for plotting radar shadow zones. 

4. To intercept and analyze new enemy sig- 
nals in order that effective jamming transmit- 
ters could be designed. 

(From a careful analysis of the results of 
these four operations, the quality, quantity, dis- 
position, and tactical usage of Japanese radar 
could be determined.) 


5. To attack and destroy enemy airborne, 
ship-borne, and land-based radar. 

6. To determine the exact instant of detec- 
tion of an Allied aircraft by enemy radar and 
hence give warning of the need for evasive ac- 
tion. 

7. To assist in determining the identity and 
location of friendly vessels. 

Investigation by Naval Vessels 

Intercept of Japanese radar from U. S. naval 
surface vessels or submarines was first at- 
tempted in August 1943. 

In the days when the Pacific war meant holding a line 
in the South and Southwest Pacific . . . radar counter- 
measures had its start. The records show that the first 
crude radar countermeasures equipment — an intercept 
receiver — ^was installed in one of our submarines oper- 
ating from Australia. The first war patrol of the sub- 
marine so equipped which produced worthwhile inter- 
cepts of Japanese radar occurred in August 1943.®^2 

At about the same time, five radar intercept 
teams equipped with prototype search receivers 
and commercially manufactured audio oscil- 
lators and oscilloscopes for pulse analysis were 
ordered to the Pacific for employment aboard 
any vessels scheduled to participate in an early 
raid against the enemy. These teams, working 
under adverse conditions, were expected to re- 
port aboard a destroyer or cruiser and make 
their installations while the force was under 
way. When the attack was over, they could be 
moved to other vessels scheduled for attacks in 
different localities. This method of operation 
had been used with some success in the Euro- 
pean Theater, but it very quickly became obvi- 
ous that Pacific requirements could not be met 
by the work of five specialized teams. 

In August 1943, then, the first of these teams 
with its makeshift equipment was placed 
aboard the cruiser Montpelier and functioned 
during the bombardment of Munda, prior to the 
landings. Japanese radars were kept under 
surveillance and valuable information for- 
warded to Washington to guide the design of 
suitably improved intercept equipment and 
jammers. In similar fashion, the other teams 
met with only moderate success in attempting 
to intercept enemy radar. The second team in- 


NAVAL RADAR COUNTERMEASURES 


323 


stalled its equipment aboard a destroyer sched- 
uled for participation in a carrier task force 
raid on Marcus Island. From August 27 
through August 31, a continuous 24-hr search 
watch was maintained with an ARC-1 receiver, 
but no definite enemy signals were intercepted. 
Their efforts were not fruitless, however, since 
experience in this raid with friendly radar in- 
dicated the need for developing ship-borne DF 
antennas at radar frequencies. On September 
18, 1943, the third and fourth teams partici- 
pated in a carrier task force raid on Tarawa 
Atoll in the Gilbert Islands. One team was 
aboard a destroyer and the other aboard the 
cruiser Minneapolis. Reports from the cruiser 
team indicated that '‘by keeping a careful watch 
on the Japanese radars on the small islands, 
it was possible for our force to evade many of 
them and at the worst know the moment when 
surprise was no longer effective because of 
radar detection.” Aboard the destroyer no 
enemy signals were heard. Again, however, 
valuable lessons were learned which guided the 
future development of fleet radar countermeas- 
ures. In particular, this team pointed out that : 

1. Analyzing equipment to determine pulse- 
repetition rate and pulse length was an essen- 
tial adjunct to the operation of an intercept re- 
ceiver. 

2. Spurious responses in the intercept re- 
ceiver should be minimized or eliminated. 

3. The characteristics of U. S. radar should 
be made available for interpreting intercept re- 
sults. 

4. Airborne radar could be intercepted at 
distances greater than 80 miles. 

By the beginning of 1944, it was clearly un- 
derstood that specialized intercept teams would 
not suffice to meet the operational RCM prob- 
lems in the Pacific. An interim installation pro- 
gram was authorized in which smaller surface 
vessels and submarines were allotted one 
AN/APR-1 receiver and one AN/APA-6 pulse 
analyzer for permanent installation. The total 
volume of equipment was not large and the 
number of trained personnel barely sufficient. 
Thus because of 

the drain on personnel and equipment for D-day in 
Europe, the Navy’s radar countermeasures effort in the 


capture of the Marianas was held down to a slight 
extension of the procedures used in the Gilberts and 
the Marshalls. . . . The Palau of)erations in September, 
1944, found our forces for the first time with sufficient 
men and material to make a coordinated radar counter- 
measures plan feasible. In this operation all radars 
intercepted in the various islands were thoroughly and 
continuously jammed to prevent them from giving the 
Japanese one scrap of tactical information. 

In October 1944, a carrier task force cruising 
off Formosa intercepted and jammed the Air 
Mark VI radar of a Japanese night torpedo 
plane. This event forced an even broader change 
in the concept of Pacific radar countermeasures. 
Strong support was given to the long-standing 
contention that radar countermeasures in the 
Pacific could not be handled as a specialized op- 
eration in which specific equipment, installa- 
tions, and personnel were assigned in small 
numbers to individual ships whose location and 
objectives would be constantly changing. The 
problem demanded that radar countermeasures 
be put on a fleet-wide basis. 

In the meantime, far-ranging U. S. sub- 
marines had found radar intercept equipment 
to be of great value against enemy airborne, 
ship-borne, and shore-based radar. Search re- 
ceivers had been employed as a defensive wea- 
pon to avoid enemy attack, and also as an offen- 
sive weapon permitting the tracking down and 
sinking of enemy vessels. “The ability to detect 
Japanese radars — shore, ship, and particularly 
airborne — long before the possibility of being 
detected by these radars even existed, meant a 
margin of safety which permitted submerging 
and other evasive tactics and saved any number 
of our underwater craft for further rampages 
among Japanese shipping.”®^^ por example, the 
following extracts are quoted from the log of a 
submarine which was on war patrol in the 
region of Anguar and Peleliu Islands. 

1 August 1944 

0400 (-9) Commenced approach to east side of Anguar 
Island. Shortly before 0500 picked up 155 Me band 
radar, searching but not training on us. 

0500 (-9) Now have two 155 Me radars trained di- 
rectly on us — one is very strong and close. Our 
range to Anguar is six miles. 

0503 (-9) Both radars seem to have us, so dived before 
they got too much dope. Spent day submerged 


324 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


eastward of 8 fathom shoal spot between Anguar 
and Peleliu Islands. 

0900 (-9) Sound picked up light screws bearing 307° 
(T), not visible from periscope. 

0905 (-9) Heard distant depth charge. Rigged for 
silent running. It is possible that a search is being 
conducted in the area — especially after the radar 
experience this morning. 

4 August 1944 

0430 (-9) Enemy radar on APR. 

0500 (-9) More enemy radar. 

2125 (-9) Enemy radar on 176 Me. Manned SJ. 

2157 (-9) SJ contact on port quarter 12,000 yards. 
Cleared lookouts from bridge. Lat. 7° — 04'N, Long. 
133° _55'E. 

2159 (-9) Contact moved rapidly to a position down 
moon and commenced coming in. Plane sighted at 
9,000 yards by OOD, coming in. 

2200 (-9) Dived with plane closing rapidly. Plane ap- 
peared to be a 2-motor bomber. His radar appar- 
ently had no trouble in staying on us and he was 
making a deliberate run from down moon. But for 
the APR we would have, at best, taken a close one. 
Especially since I did not turn on the SJ until after 
APR had contact. 

10 August 1944 

2300(-9) Dived for radar equipped plane in lat. 6° 
— 45'N, Long. 133° — ll'E. Had contact with plane 
on APR for 15 minutes during which time the 
signal became progressively stronger. Signal was 
very loud and steady when we dived. Note that 
weather was dark, overcast, with frequent rain 
squalls. Jap planes do not confine their patrols to 
clear moonlight nights. 

11 August 1944 

0420 (-9) APR signal from land-based radar. 

0530 (-9) Dived 10 miles east of Peleliu. 

2025 (-9) Dived when two strong land-based radars 
came on trained in our sector. We were 8100 yards 
from beach at this time. 

2130 (-9) Came to APR depth — radars still on. 

2355 (-9) Surfaced. No land radar operating. 

12 August 1944 

1925 (-9) Came to APR depth — land radars are on. 

2000 (-9) Tested again — radars on. Abandoned hope 
of surfacing close to islands tonight. 

2218(-9) Surfaced — seven miles from land. Land 
radars on, but sweeping. 

By the summer and fall of 1944, the pig boats would 
just as soon have come on patrol without their electric 
motors as to depart without the radar countermeasures 
equipment complete and in top-flight operating condi- 
tion; every boat was so equipped. As experience in the 
use of this equipment increased, the investigative and 
defensive uses were supplemented by still another one — 
the ability to actually locate and hunt down enemy ships 
simply because they used their radars. . . . This (type 
of operation) culminated in one particularly outstand- 
ing example: The submarine, BATFISH, picked up and 
homed in on the radar emanations from three Japanese 


submarines in quick succession. Each submarine was 
sent to the bottom on (the basis of) this information. 
From a dollars and cents point of view, the loss of 
three Japanese submarines alone paid for all our radar 
countermeasures effort in the submarine force. 

By October-November of 1944, radar coun- 
termeasures were instituted on a fleet-wide 
basis. The allowance of radar intercept equip- 
ment for each combatant ship of DE class and 
above (except submarines), including head- 
quarters ships, was established as : 

1 RDO receiver, 

1 RDJ pulse analyzer, 

1 RDP panoramic adapter, 

1 DBM direction finder, 

1 SPR-2 receiver, and 
1 panoramic adapter for SPR-2 
(under development). 

For submarines, the standard allowance 
was: 

1 SPR-1 receiver, 

1 SPA-1 pulse analyzer, 

1 SPR-2 receiver, 

1 dual-presentation panoramic 
adapter for use with both re- 
ceivers (under development), 
and 

1 direction finder (under devel- 
opment) . 

Cent. Com. Two, Annex B, and later PAC-70 
(B), established a consistent policy, doctrine, 
and plan for the use of this equipment. The 
basic doctrine stated that 


1. All ships shall make maximum use of intercept 
equipment in order to provide all possible information 
concerning enemy radars both for tactical purposes and 
to furnish data to guide the design of suitable counter- 
measures equipment, 

2. The entire radar spectrum within the capabilities 
of the radar intercept equipment available shall be 
kept under constant surveillance in order that (among 
other things) new enemy radar frequencies may be 
discovered at the first opportunity. 

3. When contact of the enemy is possible, the OTC 
shall assign RCM intercept guardships to cover the 
various bands in which enemy radar activity is ex- 
pected. The following frequency divisions and designa- 
tion shall apply: 

Guard Able 40-105 me 

Guard Baker 75-300 me 

Guard Charlie 300-1000 me 

Guard Dog 1000-3400 me 


NAVAL RADAR COUNTERMEASURES 


325 


Guard Easy Current Japanese airborne 

frequencies in the 75-300 
me band 

Guard F ox Current J apanese airborne 

frequencies in the 300-1000 
me band 

Guard George Specially designated bands 

A single receiver should normally be assigned to 
guard only one band whenever possible in order to 
reduce the delay and prevent the confusion which 
accompanies the shifting of tuning units. 

The OTC should direct ships equipped with radar 
direction finders to take simultaneous cross bearings 
on any radar signal reported by guard ships in order to 
locate the enemy radar. 

The above doctrine ivas extended to cover 
generalized intercept operations required for 
task forces at sea or at an amphibious objective. 
For a detailed description of these plans as well 
as an account of the manner in which they were 
carried out the reader is referred to subsections 
entitled “Surface Vessels’^ which appear under 
Sections 15.5.3 and 15.5.4. In summary, it will 
be noted that ship-borne radar intercept equip- 
ment performed a variety of necessary and use- 
ful functions. At the conclusion of the Okinawa 
operations, the ROM control officer for Task 
Force 52 reported that ROM equipment had 
been used for the following purposes on the 
USS Estes, AGC-12, during that operation : 

1. To alert task force to presence of enemy snooper 
planes before the planes were detected by our radar 
pickets. 

2. To further identify bogey planes which approached 
from a given direction as enemy, because of the Mark 6 
radar signals intercepted on that bearing. 

3. To determine whether land-based surface search 
radars were tracking our disposition by their sudden 
lack of rotation and increased signal strength, i.e., 
trained in our direction. 

4. To study and analyze the characteristics of various 
enemy land-based radars while in the vicinity of the 
objective. 

5. To determine the approximate location of these 
radars. 

6. To coordinate this information with that from our 
photographic intelligence in an attempt to ‘pinpoint’ 
the various enemy sets for Naval gunfire purposes. 

7. To determine the effectiveness of Naval gunfire 
and air bombardment on enemy radars by noting 
whether or not these sets came on again after being 
under fire. 

8. To further identify friendly submarines as such by 
the interception and identification of their radars. 


9. To examine skunk raids for possible enemy surface 
search and fire control radars. 

10. To determine whether or not our radar, IFF, was 
emitting a pulse of the proper size and shape. 


lo.o.s Countermeasures against Enemy 
Surface Radar 

Aircraft 

Countermeasures against Japanese ground 
radar were employed by both land- and carrier- 
based naval aircraft. However, it was not until 
the fall of 1944 that Window was used for the 
first time. Airborne electronic countermeasures 
were first used in the early part of 1945. It will 
be remembered that the British first used Win- 
dow at Hamburg in July 1943. The Germans 
followed suit on the night of September 6, 1943, 
at Bizerte. By October 5, 1943, the Japanese had 
dropped their first Window cut for 200 me on 
two simultaneous raids at Dobodura and Kari- 
wina. In this connection it is interesting to note 
that the benefits to be derived from the Pacific 
use of radar countermeasures were slow in 
realization because of the difficulty in obtaining 
enemy radar intelligence and because of the 
failure of the enemy to offer a significant radar 
threat until the later phases of World War H. 

According to naval records, the first employ- 
ment of U. S. countermeasures against Japan- 
ese radar occurred in mid-October of 1944, 
when carrier-based dive bombers attacked 
Manila prior to the invasion of Leyte. Five 
units of Navy type, CAFJ 10271 (600), Win- 
dow, guillotined to 28.2 in. for use against the 
two 200-mc GL and SLC radar thought to be in 
the Manila area, were supplied to each plane 
participating in the attack. All five units were 
to be dispensed simultaneously as the aircraft 
reached its push-over point and started the 
bombing dive. Crew reports indicated that anti- 
aircraft bursts were particularly heavy in the 
Window area, but no definite conclusion could 
be drawn as to the combat value of Window 
usage at this target. The effect on morale was 
favorable. 

In the first Philippine operation, airborne 
naval countermeasures played a very small 
part. Plans had been made to equip and utilize 


326 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


a small number of TBM’s for search and pos- 
sible electronic jamming if dangerous targets 
were encountered. Airborne jamming transmit- 
ters were not used, however, because several of 
the TBM’s were destroyed before seeing action. 

In the Palau operation, during the period 
August 26 to September 28, 1944, immediately 
preceding the invasion of Leyte, similar plans 
were prepared, but no suitable occasion was 
found for carrying them out. 

With this introduction to the use of confusion 
reflectors and electronic jamming, the naval 
air arm firmly adopted a policy of utilizing 
radar countermeasures protection at each heav- 
ily defended target which was attacked. The 
period from October to December of 1944 is 
characterized by experimentation in each air 
arm of the various fleets to evolve the most 
effective countermeasures operating procedure. 
During the carrier strikes on Shanghai, Hong 
Kong, and Formosa, carrier aircraft were uni- 
versally supplied with 200-mc Window or Rope; 
the larger planes also carried jammers. In 
some instances, makeshift Window dispensers 
were installed in fighters. Detailed records of 
the events in this period are not readily avail- 
able, but the results of this intensive experi- 
mentation are thoroughly evident in the early 
developments of 1945. With the preparation of 
a document entitled ''Cent. Com. Two, Annex 
B,^' a consistent plan, doctrine, and policy was 
achieved for the fleet-wide usage of radar 
countermeasures. 

At the beginning of 1945, then, "Cent. Com. 
Two, Annex B,'' offered the following radar 
countermeasures plans for air operations 
against enemy ground or surface vessel radar : 

1. Jamming transmitters allotted to a car- 
rier for use in carrier aircraft should be used 
when, in the opinion of the carrier task force 
commander, the effectiveness of radar-con- 
trolled antiaircraft or searchlights warrants 
the added weight involved in carrying jammers. 

2. Carrier aircraft should employ Window 
in all attacks against heavily defended target 
areas or large task forces. The first strike 
over any such area should carry Window cut 
for frequencies in accordance with the latest 
information available prior to the operation. 
Subsequent strikes should carry Window based 


on the findings of radar countermeasures inter- 
cept planes during the first and subsequent 
strikes, if any change is indicated. 

Against fire-control radars. Window should 
be dispensed immediately before reaching, and 
while over, the target area and when passing 
over heavy antiaircraft concentrations en route 
to the target. 

Example. During carrier aircraft strikes, 
each plane should drop Window cut for the 
known antiaircraft fire-control frequencies, be- 
ginning about 3 min prior to entering a dive or 
commencing a run. 

Against EW radar. Window may be em- 
ployed, if desired, in an effort to confuse the 
enemy fighter-direction systems. 

3. In the event of a fleet engagement, carrier- 
or shore-based aircraft were instructed to keep 
the surface forces covered with a Window- 
infested area at all times. The Window should 
be cut for enemy frequencies for which no jam- 
mers or shell Window was available in the sur- 
face force. Each carrier should be prepared to 
operate planes in relays to insure adequate and 
continuous coverage. 

Example. Although microwave jammers for 
use against enemy S-band radars are available 
in limited quantity, the only generally available 
defense against these radars is Window 
dropped from aircraft. 

4. For the use of shore- or tender-based naval 
aircraft, electronic jammers were collected in 
forward area radar countermeasures pools or 
at squadron bases. They were to be used when 
the effectiveness of radar-controlled antiair- 
craft fire or searchlights so warranted. 

5. Shore- or tender-based aircraft were in- 
structed to employ Window cut for fire-control 
frequencies in all attacks against heavily de- 
fended areas or against large task forces when 
the level of the bomber attack was such that 
they would be within effective gun range. 

Example. During horizontal bombing by 
large bombers. Window should be dropped at 
regular intervals by each plane during the last 
portion of the approach and when directly over 
the target area. 

Against EW radar. Window could be em- 
ployed if desired in an effort to confuse fighter- 
direction systems. 


NAVAL RADAR COUNTERMEASURES 


327 


6. Specially prepared deception or diversion 
plans incorporating the combined use of jam- 
ming, Window, and deception devices might be 
undertaken with the proper authorization. 

Example. (1) Early-warning Window may 
be employed to simulate a large number of 
planes orbiting prior to an attack. In this case, 
the Window should be sown by the plane or 
planes while circling and climbing in order to 
increase the duration of its effect on enemy 
radars. (2) Planes may sow Window in one 
area prior to making an attack in another in 
order to create false alerts and disperse enemy 
intercepting forces. 

Since the above doctrine and policy was to be 
promulgated on a fleet-wide basis, it was essen- 
tial that an adequate installation and material 
plan be instituted. Thus, in order to prepare 
naval aircraft to carry out offensive counter- 
measures operations against enemy ground or 
surf ace- vessel radar, the following jamming 
transmitters were authorized and installed. 

1. For carrier aircraft usage, equipment was 
placed aboard CV’s and CVL's to provide RCM 
installations in five TBM’s or TBF’s of each 
squadron. The following units were furnished : 

5 AN/APT-1, 

5 AN/APT-2, 

5 AM-14/APT, and 
5 AM-18/APT. 

2. For each PB4Y2 plane employed in the 
Pacific Area, the following allowance of elec- 
tronic jammers was established: 

1 AN/APT-1, 

1 AN/APQ-2, and 
1 AN/APT-5. 

3. Three planes of each squadron of other 
multiengine naval aircraft were authorized to 
carry the following equipment: 

1 AN/APQ-2. 

In addition, AN/APT-1, AN/APT-2, and 
AN/ APT-3 jamming transmitters were stored 
in forward area depots for use by these squad- 
rons when required. 

By the early part of 1945, then, a large part 
of the herculean task of procuring, transport- 
ing, and installing the necessary equipments, 
and the procurement of trained personnel, had 
been completed. Bold plans had been made for 
the amphibious assault of I wo Jima and for an 


even larger operation in the Nansei Shoto, 
known as Operation Iceberg. Numerous carrier 
air strikes would be required against the home 
islands of Japan itself. Diversionary strikes 
would be required against Wake, Formosa, and 
the China coast. The circumstances were favor- 
able, indeed, for the profitable utilization of 
radar countermeasures by naval aircraft. 

One is not surprised, then, when reading the 
action reports of the USS Bunker Hill, CV-17, 
to find that countermeasures actually played a 
large role in the Tokyo air strikes which sup- 
ported the assault of I wo Jima, as well as in the 
actual landings themselves. The following ex- 
cerpts from the log of the Bunker Hill were 
chosen as typical for each of the several car- 
riers participating. 

Feh't'VXJiry 16, 19^5 — Five TBM’s, each equipped with 
AN/APT- 1 pre-set to 198-202 Me, attacked strategic 
targets and shipping in the Tokyo area. One of the 
five aircraft was equipped with APR-1 and APA-11. 
Each VT and VB accompanying the five TBM’s was 
supplied with S- and P-band Window. Electronic jam- 
mers were used from land-fall to land’s-end. Two hun- 
dred Me and 10-cm Window was dispensed in the target 
area. No planes lost to enemy action. 

Subsequent attack was made by seven VT’s, each 
carrying 47 sleeves of 10 cm Window and 108 sleeves 
200 Me Window. 

Subsequent attack by seven more VB’s, each carrying 
50 sleeves 10 cm Window and 90 sleeves 200 Me 
Window. 

Crew Comment: All AA bursts downwind. 

February 17, 19 U5 — Radar countermeasures applied 
in fashion similar to previous day. 

Crew Comment: A A behind and below. 

In this same strike, the commander of Air 
Group 4 reported that Window was dispensed 
by F6F"s from the Mark 47 miniature bomb 
rack. AN/APT-1 and AM-18/APT were used 
for the first time in VT’s. Intense, but inaccu- 
rate, antiaircraft fire was encountered. 

D-Day for the assault of Iwo Jima was 
February 19, 1945. The shore bombardment 
groups had been active for several days with 
only a minimum of carrier air support. On the 
morning of February 19, however, at the time 
of the landings, portions of other carrier groups 
were diverted to the region of Iwo Jima in order 
to assure unquestioned air superiority and close 
support bombing for the assault troops. A large 


328 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


concentration of carrier aircraft remained in 
the Iwo Jima area until February 22, flying 
sorties at every hour of the day. Each VB or VT 
that took off was supplied with 200-mc Window, 
but no heavy antiaircraft was observed and 
hence there was no occasion for its use. The 
single Mark IV Model 3, 200-mc fire-control 
radar thought to be present on the northern 
portion of the island had succumbed, together 
with its antiaircraft guns, to previous naval 
bombardment. 

One important phase of the air operations at 
Iwo Jima, and later at Okinawa, was the pre- 
vention of enemy aircraft reinforcements either 
to the island under attack or to a near-by enemy 
island. To obviate this possibility, continuous 
watch was kept on the neighboring enemy 
islands, and Japanese air facilities through 
which replacement aircraft were staged were 
systematically destroyed. Such an operation in- 
volved night patrols for which the protection of 
RCM was highly desirable. For example, the 
commander of Night Carrier Air Group 90 
based on the USS Enterprise reports : 

In strikes on Chichi- Jima, the enemy only used their 
fire control radar during the first few strikes. Later 
they were detected turned on for a few seconds at a 
time. However, as a precautionary measure, jamming 
and Window were used during all these strikes by Air 
Group 90 on Chichi and Haha Jima, operating on the 
theory that if the enemy did turn their equipment on 
during a run, he did not gain much by it. 

Pilots, air crewmen, and administrative personnel, 
have gained much knowledge of the use of RCM and 
are highly interested in its future possibilities. 

In the interim period between the occupation 
of Iwo Jima and the assault on Okinawa, widely 
separated carrier strikes were made at such 
places as Wake Island and the airfields of 
Kyushu. In the first instance, the commander of 
Carrier Air Group 6 reports that RCM was a 
valuable adjunct to the mid-March strike on 
Wake. The antiaircraft defenses of this island 
were considered dangerous to the degree that 
an antiflak mission was planned prior to the 
main bombing attack. It was intended that four 
aircraft, utilizing bombs, machine guns, and 
RCM, attempt to neutralize the enemy's flak de- 
fenses before risking a larger number of air- 
craft. Accordingly, two TBM's and two F6F's 
took off from the USS Hancock approximately 


an hour and a half before the main strike was 
scheduled to bomb the target. These first four 
planes made their approach toward Wake at an 
altitude of 200 ft in order to avoid strategic 
early detection. At a distance of 50 miles from 
the island, they climbed to 4,000 ft, dropping 
both 100- and 200-mc Window as they flew on 
toward the objective. The Window was dropped 
at this time in order to assist in the definite de- 
tection of these aircraft and to alert the enemy 
to a sector quite foreign to the one in which the 
main bomber force would attack. At a distance 
of 10 miles from the island, flying at 2,000 ft 
and still dropping both kinds of Window, the 
TBM radar intercept operators logged two 
enemy fire-control radars at 203 and 207 me. 
Jamming was immediately begun with the 
AN/APT-l's, and within 7 min both radar sets 
had gone off the air, not to return during the 
balance of the strike mission. Bombing and 
strafing of the previously determined flak sites 
was then accomplished by the four aircraft and 
the main bomber force came in for its attack 
5 min later. No aircraft was lost to enemy ac- 
tion. 

At approximately this same time, enemy tar- 
gets on Kyushu and the Inland Sea were also 
under attack. Night Carrier Air Group 90 again 
reported substantial benefit from the use of 
RCM. 

Air Group 90 has adopted the practice of furnishing 
all aircraft with Window when operating in enemy 
areas. The VT’s are furnished with type CAFJ-10271 
(600) cut to 28.2 in. for use against 200-mc radar. The 
VF’s are furnished with Rope (CHR-2), mainly because 
it is easier for them to handle. 

In every strike the tactics may be somewhat changed 
so a set plan of procedure cannot always be used. The 
ideal way would be for special planes to sow Window 
and use jamming over the target area. When not con- 
sidered necessary or practical to assign a special plane 
for this task, Air Group 90 included at least one or two 
RCM equipped planes in each strike. All planes of the 
strike were equipped with Window and would dispense 
while making runs on the target. The planes equipped 
with jammers would jam while runs were being made. 

On the night of 19 March 1945, a VT aircraft in 
which the RCM officer was the operator, was preparing 
to make a rocket run on Saeki Air Field, Kyushu, a 
signal from an FC/SLC radar was intercepted. After 
being jammed, it was turned off and did not come on 
again. However, Window was dropped and jamming 
used while making the run as a protective measure. 


NAVAL RADAR COUNTERMEASURES 


329 


Drawing heavily on their previous experi- 
ence, naval aircraft made full use of RCM 
against enemy ground radar during the inva- 
sion of Okinawa and islands of the Kerama- 
Retto. In any invasion, but particularly in those 
at I wo Jima and Okinawa, it was necessary for 
carriers to lie offshore for extended periods of 
time in order to give continuous support to the 
beachhead. These valuable ships, in addition to 
a host of other vessels in the transport area im- 
mediately off the beaches, presented vulnerable 
targets to Japanese land-based aircraft. In 
order to protect them, as well as the invasion 
forces, all enemy airfields within range had to 
be kept under continuous attack. This was done 
both day and night by land- and carrier-based 
naval aircraft. 

The procedure usually followed was that of 
sending out three aircraft — normally two fight- 
ers and a torpedo plane — to each enemy airfield. 
These planes would then maintain a continuous 
patrol with the object of preventing enemy ac- 
tivity on the field below. To avoid accurate SLC 
and antiaircraft fire. Window, Rope, and elec- 
tronic jammers were universally employed. 

The final blow struck by naval aircraft at 
Japan's radar and electronic potential came in 
July 1945. The Third Fleet had planned a series 
of carrier strikes at important industrial 
centers on the eastern and southern coasts of 
Kyushu, Honshu, and Hokkaido. High on the 
priority list of strategic targets in each indus- 
trial center were the radar and electronic man- 
ufacturers. Bombing results were excellent. The 
United States naval air arm, which labored 
mightily to effect an electronic radar counter- 
measures program, took the next logical step, 
a direct countermeasure with high explosives. 
By this action, an important phase of the anti- 
radar war was ended before the Japanese sur- 
render. 

Surface Vessels 

Offensive electronic countermeasures against 
Japanese ground-based radar were undertaken 
no more than five times by naval vessels in 
World War H. There is no record of such 
countermeasures being employed against Jap- 
anese ship-borne radar. Quite the opposite is 
true, however, of defensive ship-borne radar 


countermeasures, which played a relatively 
large role in each contact of U. S. vessels with 
the enemy. The explanation of the slight utili- 
zation of ship-borne offensive countermeasures 
lies in the enemy’s failure to offer a significant 
surface-radar threat to attacking naval forces. 
The original purpose of Japanese radar de- 
velopment was to strengthen the air defense of 
the homeland. Until early in 1943, their effort 
was directed almost entirely toward the devel- 
opment of EW equipment, and it was only at a 
considerably later date that they succeeded in 
perfecting searchlight-control or antiaircraft 
fire-control equipment useful against U. S. air- 
craft. This latter equipment was not easily 
adapted for use against surface vessels either 
from a ground-based or ship-borne installation. 
Thus, since no serious threat was offered, it is 
not surprising that U. S. ship-borne offensive 
countermeasures were used only on a small 
scale. Because of the continuing possibility that 
such a threat might unexpectedly develop, ex- 
tensive precautions were taken. 

The first attempt by U. S. naval vessels to 
counter the effectiveness of Japanese shore- 
based radar occurred on October 25, 1944, at 
Marcus Island. In this instance, a small attack- 
ing force, in carrying out a diversionary raid, 
found It convenient to retire from the immedi- 
ate vicinity of the island at nightfall and re- 
appear for the attack at dawn the following 
day. On successive nights it was noted that EW 
radar had tracked the disposition of the surface 
force each time it retired and again on its re- 
appearance. On the final day of the attack, it 
was desired to conceal the fact that the group 
of vessels would not reappear again the follow- 
ing morning. If this retirement could be ade- 
quately concealed, the enemy might be deceived 
into directing reinforcing submarines or air- 
craft to the immediate vicinity of Marcus 
Island, thus permitting the attack group to pro- 
ceed to its base unmolested. Accordingly, on the 
night of October 25, a quantity of Ray wind 
radar targets were released in a fashion that 
would most closely simulate nighttime retire- 
ment. With luck and a favorable wind, these 
same targets might indicate an approach some 
hours later at dawn. No definite conclusion was 
drawn as to the efficacy of this tactic, but it is 


330 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


noted that the attack group proceeded to its 
base unmolested. 

Defensive countermeasures have been of 
great assistance to U. S. naval operations from 
the time of the first ship-borne installation of a 
radar intercept receiver. In August 1943, at 
such widely separated places as Munda, 
Marcus, and Tarawa, bombardment and other 
task forces employed their search receivers 
during radar silence to determine the exact time 
when each force was detected by shore-based 
EW radar. In this way, tactical surprise was 
carried a few miles closer to the objective under 
attack with the highly important provision that 
U. S. forces could usually determine the exact 
instant of their detection. In the Marianas cam- 
paign and later at Palau, extensive ship-borne 
investigations were undertaken to determine 
radar-shadow zones along which attacking ves- 
sels might approach without fear of detection 
by shore-based radar. Later on, in the periodic 
shore bombardment of the Kuril Islands, Iwo 
Jima, Okinawa, and the home islands them- 
selves, radar intercepts played a similar role, 
greatly reducing the risk of unexpected enemy 
action. 

With the sweeping decisions made in October- 
November 1944 to employ radar countermeas- 
ures equipment on a fleet-wide basis, pafet expe- 
rience of surface vessels encountering shore- 
based or ship-borne enemy radar was assessed. 
It was obvious that no serious problems were at 
that time posed by enemy ground radar. But at 
the same time, it was generally agreed that pre- 
cautions should be taken for any eventuality of 
the future. “Cent. Com. Two, Annex and 
later PAC-70 (B), “Radio and Radar Counter- 
measures and Deception,'' achieved a consistent 
plan, doctrine, and policy for the fleet-wide 
usage of radar countermeasures against enemy 
shore-based and ship-borne radar by U. S. sur- 
face vessels. 

A plan such as the following was offered for 
task forces at sea which combined the comple- 
mentary functions of radar and RCM : 

1. Radar and RCM 'pickets should be sta- 
tioned from 20 to 40 miles ahead of the force, 
either on both bows or in the direction of the 
most probable enemy attack. These pickets 
should be equipped with sufficient radar and 


RCM equipment to conduct a search either by 
radar, for enemy air or surface targets, or by 
intercept receivers, for enemy radar signals. 
Each ship should be prepared to spot-jam an 
enemy radar when directed. 

2. Screening destro'yers should be disposed in 
such a manner that they can search for enemy 
radar signals, barrage- or spot- jam when or- 
dered, or deceive the enemy by means of Gulls, 
Kites, or shell Window. 

3. Larger ships were required to perform a 
variety of functions, including supplementary 
RCM search, jamming, or deception, in addition 
to radar tracking or fighter-direction control. 
In particularly large dispositions, radar jam- 
ming by ships in the screen was to be supple- 
mented with jamming by interior units in order 
to create maximum confusion on the enemy’s 
radar presentation and lend additional protec- 
tion to the interior units if the enemy should 
penetrate the screen. 

All ships having RCM equipment were as- 
signed intercept and jamming duties in one or 
more of the following RCM guard bands : 


Able 

40- 105 

me 

Baker 

75- 300 

me 

Charlie 

300-1,000 

me 

Dog 

1,000-3,400 

me. 


4. The overall coordination and control for 
the use of radar and RCM equipment in a task 
force at sea fell to the Officer in Tactical Com- 
mand [OTC], who might delegate actual con- 
trol to a force RCM control officer aboard a 
vessel with superior RCM facilities. In combat, 
this officer might follow one or more of the 
standard tactics (or, as sometimes happened, 
devise and approve a new one on the spot). 
Standard tactics included 

1. Screening of the entire force by shell Win- 
dow or aircraft-dispensed Window in the event 
that enemy radars were encountered for which 
no jammers were available. 

2. Deception by Gulls or other reflectors at 
night or under conditions of restricted visibility. 

3. Screening of the entire force, in the event 
of a fleet engagement, by the use of all available 
jammers against all enemy radars encountered. 


NAVAL RADAR COUNTERMEASURES 


331 


with particular emphasis on enemy fire-control 
radars. 

In order to permit the carrying out of this 
generalized plan on a fleet-wide basis, an instal- 
lation and material program of sweeping pro- 
portions was instituted by January 31, 1945. 
The following offensive RCM equipment was 
authorized : 

1. For all headquarters ships, cruisers, air- 
craft carriers, battleships, and destroyers of the 
445 and 692 class, the following radar jammers : 

1 TDY transmitter (60 to 1,200 me) 

1 S-band jammer (under development) 

2. Suitable supplies of Window-loaded pro- 
jectiles covering known enemy fire-control fre- 
quencies for all combatant vessels of DD class 
and above. 

This program, because of its comprehensive 
nature, was familiarly known as the “Ultimate 
Installation Program’"; its completion was to 
cover a period of several months. But the insur- 
ance value of RCM equipment could ill afford a 
delay of this length. Even before the promulga- 
tion of this ultimate program, interim installa- 
tions had been proceeding at a rapid rate. Jam- 
ming equipment originally designed for aircraft 
usage had been cleverly adapted to ship-borne 
installation. For example, two or more of the 
equipments listed below, 

AN/SPT-1, 

AN/SPT-4 or AN/APQ-2, 
AM-14/APT, 

AM-18/APT, 

had, by the late fall of 1944, been installed 
aboard the following : 

7 battleships 
3 cruisers 

12 carriers 

44 destroyers 

6 headquarters ships (AGC) 

3 YMS 
3 LCI (G) 

45 LCI (L) 

2 DM. 

Thus, in the early part of 1945, naval forces 
were in an excellent position to reap the benefits 


of the past countermeasures effort. Generalized 
RCM tactics and doctrine had kept pace with an 
adequate installation and training program to 
a degree that gave U. S. forces an overwhelming 
advantage in that phase of electronic war- 
fare involving countermeasures against enemy 
shore-based or ship-borne radar. Such an op- 
portunity presented itself with the plans for 
the invasion of I wo Jima. 

Previous reconnaissance of Iwo Jima, both 
by intercept receivers and aerial photography, 
had revealed the definite existence of as many 
as four radars. With one exception, a Mark IV 
Model 3, all equipments were believed to be of 
the EW type operating either in the region of 
100 or in that of 150 me. No intelligence specific 
to Iwo Jima indicated the presence of gun- 
control radar suitable for directing shore bat- 
teries onto naval targets. Generalized intelli- 
gence on the state of Japanese radar develop- 
ment substantiated this conclusion, but left 
some margin for doubt. With this information, 
an operational order was written into the in- 
vasion plans which directed the establishment 
of a 24-hr intercept guard from 40 to 3,400 me 
according to the policy of “Cent. Com. Two, 
Annex B.” Offensive countermeasures were to 
be employed only at the discretion of the OTC, 
since the need for employment against shore- 
based radar, judged in the light of previous 
intelligence, was not thought to be great. Other 
portions of the operational order were con- 
cerned at length with the more dangerous prob- 
ability of attack by enemy ASV-equipped 
bombers. (See subsection “Surface Vessels” of 
Section 15.5.4.) 

As the operation commenced on February 16, 
the amphibious assault force. Task Force 52, 
engaged itself in an intensive shore bombard- 
ment. During this time, a 24-hr intercept watch 
was maintained and a complete log of the 
island’s radar operations secured. From this it 
was found, generally, that the EW equipments 
were operated only at night after bombardment 
had ceased, most likely attempting to monitor 
the disposition of our forces in the hours of 
darkness. The period of operation of any one 
radar was irregularly intermittent. Numerous 
attempts were noted to change the character- 
istics of these radars, probably in an effort to 


332 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


confuse our intercept activity. The single fire- 
control radar on the island was observed to op- 
erate only at night in the presence of Allied 
aircraft. 

On the morning of February 18, a signal was 
intercepted with characteristics similar to the 
Japanese Air Mark VI (ASV) and some ships 
began jamming on a frequency of 152 me. 
Further checking aboard the USS Estes, AGC- 
12, indicated that this was a stationary ground 
radar located on the northeast portion of the 
island, probably of the Mark I Model 3 type. 
Jamming was immediately secured since no 
purpose was being served, and since, in the 
confusion, undesirable interference to U. S. 
radars such as the SC and SK was created. 

Before beginning the short bombardment 
phase of the operation, the EW radars of the 
island had been evaluated as a necessary evil 
of no great importance to the enemy’s immedi- 
ate tactical position. With this evaluation, no 
particular emphasis was placed on their destruc- 
tion by naval gunfire. In fact, it was hoped that 
they might be captured intact and serve as an 
additional sourcq of intelligence. In the light of 
this, it is particularly interesting to note that 
by noon of February 18 the Japanese had be- 
come aware that their radar sets were not being 
used as bombardment targets. Quickly taking 
advantage of this fact, numerous stores and 
some lighter weapons were concentrated at 
these locations. This change in disposition of 
enemy defenses was easily detected from aerial 
photographs and a good portion of the afternoon 
of February 18 was allotted to the systematic 
destruction of each of the island’s radars and its 
surrounding area. By the night of February 18, 
the last of the enemy’s ground-based radar had 
been destroyed. The 24-hr intercept guard was 
necessarily continued, however, to assist in de- 
fense against airborne enemy radar. 

Following the assault of Iwo Jima, a number 
of diversionary strikes were undertaken to pre- 
pare the way for the later invasion of Okinawa. 
The record indicates that these strikes, with 
one exception, involved no use of offensive 
countermeasures against ship- or shore-based 
radar. The single exception occurred at Zam- 
boanga on the night of March 9, 1945, when the 
commander of Task Group 74.3 ordered the USS 


Boise, CL-47, to jam a signal which had first 
been intercepted on 600 me and slightly later on 
606 me. An identification of this signal was 
never satisfactorily made, nor were the results 
of the jamming ever definitely evaluated. This 
operation is notable, however, because it repre- 
sents an unpredicted, unexpected event in which 
the precautionary program for offensive ship- 
borne countermeasures was called into use. 

The final incident in the story of ship-borne 
countermeasures against enemy ground radar 
came with the planning and execution of the 
invasion of Okinawa. An elaborate reconnais- 
sance of all features of the enemy defense in the 
Okinawa-Gunto had been carried out before 
definite plans were consummated for Operation 
Iceberg. This reconnaissance had included radar 
intercepts by aircraft, surface vessels, and sub- 
marines, as well as small-space and large-scale 
photographic reconnaissances permitting de- 
tailed pin points of several radar sites. Assess- 
ment of this information revealed that the 
enemy’s radar defense was probably limited to 
EW equipment. A total of 10 to 12 such sets 
was eventually found, including the 7 listed 
below : 

2 Mark I Model 3 
2 Mark I Model 1 
2 Mark B 
1 Mark CHI 

In planning the operation, past experience, 
including Iwo Jima, strengthened the conclu- 
sion that ship-borne jamming of EW ground 
radars would serve no useful purpose. Accord- 
ingly, the operational order specified the con- 
ventional 24-hr intercept guards, with the ad- 
dition of definite jamming plans for protection 
against enemy airborne radar. (See subsection 
entitled “Surface Vessels” of Section 15.5.4.) 

The operation itself commenced with the 
simultaneous invasion of the Kerama-Retto and 
the shore bombardment of Okinawa on March 
26. During this period, a comprehensive log was 
kept of all enemy radar operation and the task 
was begun of keying known radar locations 
with radar intercepts. As at Iwo Jima, the op- 
erating periods of enemy radar were irregularly 
intermittent, with some preference of nighttime 


NAVAL RADAR COUNTERMEASURES 


333 


operation. Frequency, pulse widths, pulse-repe- 
tition rates, and even the physical locations of 
several Okinawa radars were changed without 
notice. During shore bombardment periods, no 
more than three radars were known to operate 
at any one time. Moreover, it was found that the 
enemy had a coordinated warning net to the 
extent that operation of individual radar sets 
could be shifted up and down the southwest 
coast of Okinawa in accordance with the center 
of U.S. naval activity. With the extended oppor- 
tunity to observe Japanese ground radar at 
close quarters, naval RCM operators drew sev- 
eral interesting conclusions. 

1. The changing characteristics, location, and 
intermittent operation of enemy radars were 
thought to stem from the Japanese awareness 
of RCM facilities aboard U.S. naval vessels. It 
was believed that the Japanese hoped to conceal 
by these means the true number of radars in 
operation within a given area and to hinder 
accurate location of any particular set. 

2. The Mark B radar, as exemplified by a par- 
ticular set in the vicinity of Yonabaru, appeared 
to be capable of tracking large surface vessels 
at ranges of 17 to 20 miles. 

3. The Mark I Model 3 radars behaved in a 
manner which led one to suspect their use as a 
source of beamed energy which, if coordinated 
in frequency with the Air Mark VI (ASV) or 
similar type of gear, might be used to guide 
enemy aircraft or suicide boats to U.S. surface 
dispositions. 

The latter conclusion, if true, represented a 
situation sufficiently dangerous to the vulner- 
able collection of ships immediately offshore 
that it was made the subject of an extended ex- 
periment involving electronic jamming of shore- 
based radar from surface vessels. The USS 
Robert H. Smith, DM-23, and the USS Wads- 
worth, DD-516, took turns jamming a particu- 
larly suspicious 93-mc mobile search radar from 
May 23 to June 6. Throughout this period, the 
behavior of this radar was closely scrutinized 
at the time of an enemy night air attack, and, 
with time, its correlation either in direction of 
scan with the experienced air attacks or in co- 
incidence in frequency with enemy airborne 
radar was finally judged insignificant. Jamming 
was discontinued at this time with no definite 


conclusion as to the degree of coordination be- 
tween enemy air and ground radar for the night 
location of surface targets. 

In essence, the main contribution of RCM 
to the Okinawa invasion involved offensive 
countermeasures to airborne enemy radar which 



Figure 4. RCM and radar antenna installation 
of the aftermast of a destroyer. Pictured here, 
from the base upwards, are the following RCM 
antennas: 1 TDY-IA, S-band, transmitting 
antenna; 1 TDY, low-frequency, rotating-head 
antenna (transmitting and receiving) ; 1 AS- 
45A/APR-6, high-frequency, wave-guide, receiv- 
ing antenna ; 1 DBM-1, high-frequency, rotating- 
head, receiving antenna; 1 DBM-1, low- 
frequency, rotating-head, receiving antenna; 2 
CAGW-66132, low-frequency, stub-type, receiving 
antennas with ground plane; 2 CAGW-66131, 
cone-type, higher-frequency, receiving antennas 
with ground plane; 1 AS-44/APR-5, cone-type, 
S-band, receiving antenna. 

are described in Section 15.5.4. As an adjunct to 
this function, the conventional intercept guards 
were maintained in order to discover, if possible, 
the operating procedures which governed the 
use of enemy EW radar. Apart from the ex- 
amples of the preceding paragraph, this inter- 


334 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


cept operation further assisted by eliminating 
a particularly annoying Mark CHI radar. It was 
discovered that this radar in the vicinity of 
Chinen Saki was being used deliberately to jam 
the voice communication circuit of the TBS 
equipment operating at 72.2 me. Direction-find- 
ing fixes obtained from the TDY rotating an- 
tenna were sufficient to permit low-level recon- 
naissance photographs to pin-point the enemy 
set, and naval gunfire put it out of action. 


Countermeasures against Enemy 
Airborne Radar 

Countermeasures against Japanese airborne 
radar were employed by U.S. aircraft, surface 



Figure 5. Japanese patrol bomber probably 
equipped with ASV type radar. 

vessels, and submarines. From the record of 
naval operations, it appears that the Japanese 
airborne radar, in actual combat, proved to be 
the most dangerous of all Japanese radar in 
World War 11. 

The particular equipment, known as the Air 
Mark VI, which threatened naval forces was not 
far advanced by U.S. standards. In fact, it was 
similar in many respects to the first ASV equip- 
ment used on U.S. patrol aircraft at the out- 
break of hostilities, which was finally judged 
obsolete by the middle of 1942. In common with 
all types of ASV radar, the Japanese Air Mark 
VI permitted reconnaissance aircraft to monitor 
the movements of fleet units in a vastly in- 
creased search sector. A target, once found. 


could be kept under surveillance at distances 
great enough to hinder interception or to pre- 
vent the ranging of surface antiaircraft guns. 
(Airborne radar, in comparison with surface 
radar, has a decided range advantage because 

(1) it operates on an “elevated platform’" and 

(2) the normal ASV target, a ship, has a much 
larger echoing area than an aircraft.) In par- 
ticular, the task of naval combat air patrols in 
destroying Japanese Mark Vl-equipped spotter 
aircraft was rendered much more difficult since 
more and more patrol aircraft were required to 
protect adequately any given disposition of 
vessels. Moreover, Japanese night torpedo 
planes often used ASV-type radar in the initial 
phases of their attack. Later on. Kamikaze at- 
tacks were sometimes directed from Mark VI- 
equipped aircraft. For these reasons, then, 
enemy airborne radar constituted a serious 
threat to U. S. naval operations and considerable 
countermeasures effort was successfully ex- 
pended to deny the enemy full use of this equip- 
ment. 

Fortunately, the first operational use of this 
enemy equipment did not occur until early Oc- 
tober of 1944. As in the case of nearly every 
Japanese radar, U.S. forces had ample advance 
information that such equipment might soon 
become operational. It will be remembered that 
in April 1944 the receiver portion of an early 
Air Mark VI radar was captured at Hollandia. 
In the invasion of Saipan, a complete equipment 
was found intact together with its spare parts. 
From a Kate found in the same hanger with the 
Saipan equipment, the antenna and installation 
practices were also known. Early models of this 
set had operating characteristics of 


Frequency 
Pulse-repetition fre- 
quency 
Pulse length 
Peak power output 


150 me 

250 (later models had 
a prf of 1,000) 

10 |isec 
5 kw. 


Later on, by the end of November 1944, a con- 
siderably improved model known as the Mark 
VI Model 4 was captured on Mindoro. Because 
of the numerous operational encounters involv- 
ing this equipment, the importance of deter- 
mining its exact capabilities was clearly under- 



NAVAL RADAR COUNTERMEASURES 


335 


stood and extensive field tests were performed 
in the Hawaiian area by ComAirPac to obtain 
an accurate evaluation both of the set’s operat- 
ing capabilities and of its susceptibility to jam- 
ming. 

It is believed that the Air Mark VI equip- 
ment was developed and used principally by the 
Japanese Navy. A similar equipment, known as 
the Taki Model I, operating on 200 me, was 
later developed for use in Japanese Army air- 
craft. 

Aircraft 

Since the ability of Japanese airborne radar 
to detect and track aircraft targets was slight 
(that is to say, its performance as an Al-type 
equipment was poor) , it would not be expected 
that U.S. aircraft need employ offensive coun- 
termeasures against this particular set on any 
great scale. In point of fact, this proved to be 
true, and there is no record of any naval opera- 
tion in which an airborne jamming transmitter 
was used against enemy ASV-type equipment. 
On the other hand, intercept equipment in naval 
aircraft provided some spectacular examples of 
a newly developed AI tactic. In general, the 
enemy plane, when using its radar in the search 
for surface targets, emitted a signal that could 
be picked up on a radar receiver at distances 
greater than 60 miles. With the use of airborne 
DF systems such as the AN/APA-24, or better 
still, the AN/APA-17, it was sometimes possible 
for an interception to be effected. Such an inter- 
ception procedure was based on the preliminary 
direction of the interceptor aircraft in accord- 
ance with DF cuts on a definitely identified Air 
Mark VI signal. Following an interception 
course, the range was closed until the victim 
was within radar range of the interceptor plane. 
From this point on, the technique was in all 
ways similar to conventional radar interception 
without ground control. 

The first, and certainly the most spectacular, 
example of this type of tactic occurred in the 
fall of 1944 near Formosa. The incident is 
described here in the words of the commanding 
officer of VPB 116, a PB4Y search squadron 
then based on the island of Tinian. 

One interesting use of ROM equipment came up at 
that time. The Emily is using radar and apparently it 


is using radar similar to our original Easy gear, which 
has a homing position forward and search antennas on 
either beam, alternating between the two. One of our 
planes on a sector search out toward Formosa had been 
instructed that there was a surfaced crippled submarine 
coming back escorted by three others. He was about 
800 miles from Saipan at the time. The searcher’s 
orders were incidentally to give any air cover he could. 
When our plane was about abeam of this submarine, 
and had the submarine on his radar screen, he picked 
up on his ROM equipment an indication of a transmis- 
sion, which appeared to the technician running the scope 
as Japanese airborne radar. It had the frequency that 
the Japanese submarines have used, but the PRF count 
was a good bit different. He suspected it to be airborne, 
as he got a peculiar build, then black out, then a weaker 
signal, and then black out, which indicated that a 
switch from search to homing antennas took place. He 
has previously been acquainted with this type from the 
old PBY equipment. He drew the pilot’s attention to 
it, made a very rough. I’d say guess, but he said esti- 
mate, that it was ahead about 90 miles. How he got 
the distance I don’t know, except by what he claimed, 
signal strength. He homed the pilot toward it. After 
about 15 to 20 minutes he told the pilot that they were 
very close; the pilot dropped his search gear and picked 
up an enemy aircraft blip on the search gear within a 
six mile circle, obviously below him as he was on top 
of a .6 cumulus. All the pilot did was get lined up, push 
the nose over, and man all guns. Wlxen he came out of 
the clouds he was right over an Emily, which at that 
time was about 20 miles from our crippled sub. The 
Emily used the old tactics of jettisoning his depth 
charges as the old PBYs used to do. Fortunately, the 
pilot was an ex-PBY man and jumped over the explo- 
sion and kept coming in. That encounter, I thought, was 
a rather unusual use of RCM at the time, but it is going 
to be used that way consistently in the future as Jap use 
of radar on their aircraft becomes more common. For 
that reason, the RCM should be standard on our planes 
now, and I think we are getting them in all our PB4Y-2s. 
It is going to be an excellent addition for search. You 
can pick Japs up from 90 to 100 miles away with it. 

The possibility that RCM intercept receivers 
and DF or homing antennas offered a new inter- 
ception technique was welcome news that 
spread rapidly through the fleet. By the end of 
1944, numerous elements of the naval air arm 
had experimented with this possibility, often 
with makeshift equipment designed and in- 
stalled at sea or in the forward areas. For ex- 
ample, the commanding officer of Night Carrier 
Air Group 41, based on the USS Independence, 
reports : 

Our own RCM equipment was just getting out in 
quantity when I left. We had three planes with it in- 


336 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


stalled and it apparently worked very well. We mounted 
an experimental radar homing antenna in a TBM in 
connection with the RCM receiver, and on its first flight 
it picked up a Jap plane off the coast of China, about 
50 miles away, and got a bearing to within 5 degrees. 
Coming back in towards our own Fleet it picked up the 
SK at 185 miles at 12,000 feet. There are very great 
possibilities in the use of gadgets of that kind where 
our own planes home on enemy transmissions. The 
enemy apparently thinks we have a lot more equipment 
of that sort than we do, however, because their snoopers 
are coming in to within 15 to 20 miles of the formation, 
staying right on the water, leaving their radar off, and 
then popping up every 15 minutes or so, turning their 
radar on for about 45 seconds, taking a real good look 
and then going back down. The problem of night inter- 
ception is getting more and more difficult as the enemy 
learns more and more about it; so we have to hop fast 
to keep up with them. . . . 

The radar countermeasure equipment we got seems 
to be very satisfactory. It was easy to install, easy to 
use. ... I won’t go into that any more except to re- 
iterate what I mentioned before about the use of that 
countermeasure receiver with homing antennas. That is 
going to be very important in the future. 

By March 1945 this tactic had been accepted 
and was actually included in the operational 
orders of Night Carrier Air Group 90 based on 
the USS Enterprise. From the following excerpt 
from a report by Air Group 90’s RCM officer, 
it will be obvious that, though the tactic 
was accepted and utilized, experimentation con- 
tinued. , 

The last two operation plans have carried a plan 
whereby an RCM plane was to attempt to intercept the 
radar signal from an enemy aircraft, take a bearing on 
it, and proceed in that direction until it could be picked 
up by radar. Then an attempt was to be made to vector 
a fighter after the enemy plane. 

Air Group 90 tried this once north of Iwo Jima. Two 
planes were sent out when an attack was expected to 
try and detect the approach of enemy planes and give a 
warning before they could be picked up on the ship’s 
radar. No airborne signals were intercepted and no 
attack developed. 

The first indication had by this group that something 
might be accomplished along this line came from a 
report by one of the radar officers on a flight to the 
Inland Sea. This officer intercepted a signal which he 
believed to be airborne. Its bearing was 5 degrees port. 
He informed the radar operator to be on the lookout 
for an aircraft target on his scope and it was only a 
matter of seconds before the radar operator did pick 
up an aircraft about 5 degrees to port, distance 6 miles. 
Regrettably, no follow-up was made on this contact as 
a different objective was in view. 


It is suggested that tests be made on these lines where 
facilities are to be had, as it might facilitate the devel- 
opment of the techniques to be employed. Also, along 
this same line, it is suggested that operators be taught 
how to distinguish an airborne signal from that of a 
land based air search radar. None of our RCM men had 
received anything along that line and there is not much 
chance in an advanced area to show them the difference 
until they actually see one. Then, the operator is not 
always sure of himself. 

Another new possibility suggested itself recently. Six 
of RCM VT aircraft returned from a mission and found 
the force, including the Enterprise, under attack. 
While orbiting and waiting for the attack to be over, at 
least three of the RCM operators intercepted signals 
which they believed to be airborne. No jamming was 
done because it was feared that confusion to some of 
our own ships might result. The fact rates consideration 
that in a similar situation and upon direction from the 
ship, RCM planes might jam on the enemy frequency 
and aid the outcome considerably. It has been noted in 
other reports of instances where enemy aircraft turned 
away when their radar was jammed by surface units. 

Surface Vessels 

Of all Japanese radar, the enemy airborne 
equipment, it will be recalled, offered the great- 
est threat to U. S. naval operations. Ship-borne 
countermeasures were consequently employed 
on a large scale to deny the enemy full value 
from his ASV-type equipment — the Air Mark 
VI, the Taki Model I, or similar sets. As early 
as April 1944, U. S. forces were alert to the 
fact that enemy ASV equipment might soon be- 
come operational. Fortunately, interim installa- 
tion and training programs were proceeding in 
the fleet on a precautionary or insurance basis 
(see subsection entitled “Surface Vessels’’ of 
Section 15.5.3). Jamming transmitters such as 
the AN/SPT-1, AN/SPT-4, AN/APQ-2, AM- 
14/ APT, and AM-18/APT, originally designed 
for aircraft usage, had been cleverly adapted to 
ship-borne installation. By the middle of Sep- 
tember 1944, over 50 such interim installations 
had been completed. 

In the first week of 1944 

a carrier task force cruising off Formosa was attacked 
by Japanese night torpedo planes equipped with ASV- 
type radar. This happened “only once”; when the Japa- 
nese returned the next night it was quite a different 
story. Rapid modifications had been made ‘in existing 
jammers to cover the Japanese airborne radar fre- 
quencies. As soon as the signals were picked up the 
next night, jamming was commenced. The effect was 


NAVAL RADAR COUNTERMEASURES 


337 


startling. The hitherto intrepid Japanese pilots literally 
blinked in amazement. This was something new, some- 
thing not looked for. Oif went the radars and the planes 
commenced orbiting aimlessly at a safe distance from 
the task force. Those who were not shot down sub- 
sequently by our night fighters, took home a very per- 
plexing tale. . . . 

The reports of this fleet action, when digested 
and evaluated, gave unequivocal support to the 



Figure 6. Typical ship-borne installation of a 
TDY-IA, S-band, jamming transmitter and 
antenna-control system. 


long-standing contention that radar counter- 
measures in the Paciflc could not be handled as 
a specialized operation in which specific equip- 
ment, installations, and personnel were assigned 
in small numbers to individual ships whose 
location and objectives would be constantly 
changing. The problem demanded that radar 
countermeasures be put on a fleet-wide basis. 

As a result, the Electronics Division in the 
Office of the Chief of Naval Operations, plus the 
Electronic Sections of the Bureau of Aeronau- 


tics and the Bureau of Ships, authorized and 
implemented an ultimate RCM program. This 
was the inception of a program which, some- 
time later, was outlined for the tactical aspect 
in Cent. Com. Two, Annex B and PAC-70(B), 
and for the material aspect in CM and D 
Bulletin-Issue Number 14. 

Before this program could be put into opera- 
tion, however, much experience was to be gained 
from the numerous encounters with the Jap- 
anese Air Mark VI which followed closely on 
the heels of its first operational use. The small- 
scale interim program was to pay dividends 
many times in excess of its original investment. 

At the time of the first Philippine landings, 
portions of the Third and Seventh Fleets were 
disposed off Leyte Gulf and in the Surigao 
Strait. October 19, 1944, signals the first in- 
stance in which several radar-equipped Jap- 
anese aircraft operated simultaneously against 
large portions of the U. S. Fleet. During the 
early morning hours, Japanese spotter aircraft 
watched fleet movements with the aid of radar. 
The USS Leutze, DD-481, intercepted and 
jammed an Air Mark VI signal, and the Jap- 
anese reaction was similar to the first instance 
off Formosa. That night, as a destroyer task 
group approached the shores of Leyte Gulf, Jap- 
anese Betty s and Vais, serving as night torpedo 
planes, approached for a radar-assisted attack. 
All available AN/SPT-4’s in the force were 
tuned to the frequency range 152 to 157 me, and 
jamming was commenced. In the face of this 
barrage no torpedo attack was made. The enemy 
aircraft approached no closer than 10 miles and 
one by one turned off their radars, orbited, and 
finally returned to base. In the succeeding days, 
similar attacks, either at night or under con- 
ditions of low visibility, were made with the 
aid of the Air Mark VI. The Japanese, at first 
thoroughly confused by the surprise of jam- 
ming, began to experiment with antijamming 
[AJ] techniques. On October 21 the USS Roh- 
inson, while jamming an Air Mark VI, noted 
that the enemy signal when jammed would turn 
off and reappear slightly later on a frequency 
some 21/2 me higher. The RCM operator kept 
pace with the shifting of the enemy radar fre- 
quency from 152 to 160 me in four successive 
steps. Tiring of this fruitless battle of wits. 



338 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


the Japanese attacker went home discouraged. 
Other attacks were noted in which the enemy 
operator, in the face of jamming, would turn 
off his equipment, wait for the jamming to 
cease, and then turn it on quickly for a free 
look. Even as the enemy in this particular local- 
ity was becoming educated to AJ measures, 
U. S. operators were simultaneously becoming 
more skilled in their offensive RCM operations. 

By the evening of October 24, when it was 
known that a Japanese task force was on its 
way to attack, all U. S. vessels were alerted and 
on the watch. Enemy spotter aircraft were ex- 
pected momentarily. The USS Hutchins and the 
USS South Dakota both intercepted enemy ASV 
signals at this time and successfully jammed 
them, thus giving U. S. forces added time to 
maneuver before finally engaging the enemy 
force. The ensuing battle of Surigao Strait is 
well known. Japanese radar played a very small 
part in this and the later phases of the first 
Philippine operation. As the engagement 
started, ship-borne enemy radars were inter- 
cepted, but one by one were heard to leave the 
air after an attack by U. S. aircraft. Japanese 
aircraft, disillusioned by their previous experi- 
ence with U. S. jamming, placed less and less 
reliance on their ASV radar as their tactics 
became more and more bold. In the period from 
October 19 to October 30, enemy aircraft ran 
the full gamut of attack philosophy: All the 
way from that of staying away from the U. S. 
forces during bombardment periods to that of 
full Kamikaze action. When the enemy became 
committed to the latter tactics, his use of air- 
borne radar declined to the vanishing point. 

As the reports of this and other fleet actions 
returned to the Commander-in-Chief, U. S. Pa- 
cific Fleet, their assessment substantiated the 
sweeping decision made in October-November 
1944 to employ radar countermeasures equip- 
ment on a fleet-wide basis. In large measure, 
these reports assisted in the preparation of a 
consistent plan, doctrine, and policy for the 
tactical employment of the large quantity of 
countermeasures equipment then being in- 
stalled. One is not surprised, for example, to 
learn from Cent. Com. Two, Annex B, that 

as of December 1944, the principal enemy radar threat 
is the use of 150-160 megacycles for airborne radars in 


snoopers and torpedo planes. Barrage jamming in this 
band can be accomplished by modified SPT-4 (rug) jam- 
mers on ships without RCM personnel. Spot jamming 
ships would also be required whenever barrage jamming 
is employed; these spot jammers should be on ships 
with RCM personnel, intercept receivers and jammers 
capable of jamming enemy signals between 100-160 
megacycles. 

Recommended procedure is for RCM technical per- 
sonnel to stagger- tune the barrage jammers to cover 
the 150-160 megacycle band. The frequency spread be- 
tween jammers should not exceed 2.5 megacycles when- 
ever possible. 

Jamming tactics against enemy airborne 
radar were envisaged in the instance of task 
forces at sea and of amphibious land operations. 
Specific plans applicable to the former instance 
are set forth in the subsection entitled '‘Surface 
Vessels'^ under Section 15.5.3. For the latter, 
plans similar to those below were conceived. In 
both cases the problem of denying the enemy 
full use of his ASV-type radar involved 

1. The earliest possible interception and 
identification. 

2. The rapid inception of appropriately 
tuned spot- or barrage-jamming signals. 

Small vessels, usually of the destroyer class 
had been singled out to serve as pickets for 
early-warning radar purposes. The maneuvers 
of a radar picket were quite consistent with the 
need for early interception and identification 
of enemy radar and the complementary func- 
tions of radar and RCM equipment were quickly 
realized. The result was a combined radar and 
RCM picket. The rapid creation of a jamming 
signal was a problem of adequate communica- 
tions and trained operators. Fleet plans for 
radar and RCM pickets included the following. 

1. One of the most important units in the RCM tech- 
nical organization is the RCM picket ship whose func- 
tion is to provide the OTC’s RCM control with early 
information on enemy radar activity. 

2. An RCM picket ship should have RCM intercept 
equipment and adequate communications facilities. 
Trained personnel are required, and radar jammers are 
an additional desirable feature. Suitable ships should 
be fitted to serve as combined Radar and RCM Pickets 
whenever practicable. 

3. Normally RCM pickets should be stationed far 
enough away from OTC RCM control to allow time 
after receipt of intercept information to initiate jam- 
ming action to confuse or frustrate a threatened attack. 

4. Two types of Radar and RCM Pickets were dis- 


NAVAL RADAR COUNTERMEASURES 


339 


tinguished: Distant pickets should maintain continuous 
intercept guards for enemy airborne radar and be pre- 
pared to spot-jam when directed. Other pickets should 
maintain intercept guards for all frequencies from 
40-3400 megacycles without special regard to the 150- 
160 me enemy radar band. 

For amphibious operations the following 
technique in the use of radar and RCM pickets 
in the region of an amphibious objective was 
recommended. 

1. One or more destroyers should be stationed as a 
distant picket about 50 miles from the objective or 
transport area in the direction of possible enemy air 
attack. 

2. Fighter Director destroyers, as available, should 
be stationed around the objective as Radar and RCM 
Pickets roughly at a 15 mile radius from the transport 
area. Stations assigned should be selected with due 
regard for the topographical features of the objective 
as well as direction of probable enemy air attack. 

3. Ships in the transport area other than the flag 
ship of the Attack Force Commander may be used to 
supplement the Radar and RCM Pickets. 

4. The Attack Force flagship (AGC) should main- 
tain a continuous overall RCM guard and should carry 
the Force’s RCM Control Officer as well as the Force’s 
Fighter Director. 

5. Small craft and landing craft fitted as spot jam- 
ming and barrage jamming ships, should be placed 
about two miles from those ships to be screened and 
at about two-mile intervals around them. If an in- 
sufficient number of jamming ships is available to sur- 
round the area to be screened, a group of several 
barrage jammers and at least one spot jammer should 
be placed two or three miles toward the direction of 
the enemy’s most probable approach. 

With the invasion of Luzon, the numerous 
lessons learned in the U. S. Fleet were put to 
excellent use in denying the enemy full value 
from ASV-type equipment. At Lingayen Gulf, 
during January 1945, Admiral Kincaid, Com- 
mander Luzon Attack Forces, was stationed 
aboard the USS Wasatch, AGC-9. The force 
RCM control officer was also aboard this vessel 
and this close contact with the OTC resulted 
in the first blanket plans for the jamming of 
Air Mark VI signals, in the frequency range 
150 to 160 me. The jamming of enemy airborne 
radar from vessels of this force became a com- 
mon occurrence. Within the attack force itself, 
more detailed plans were made for the carrying 
out of the OTC’s blanket authorization. For 
example, the Commander of the Second Carrier 


Task Force authorized jamming of all signals 
in the frequency range 150 to 160 me with Air 
Mark VI characteristics, providing the enemy 
aircraft was within 45 miles of U. S. vessels. 
Such authorization was of great assistance, as 
is seen in a report from the USS Bismarck Sea, 
CVE-92. This vessel was constantly shadowed 
by enemy spotter aircraft at night. In every in- 
stance in which the spotter aircraft were radar- 
equipped, electronic jammers were immediately 
used. In no case did the enemy aircraft ap- 
proach closer than 10 miles. 

With the preparation of plans for the inva- 



Figure 7. Typical ship-borne installation of 
DBM-1, rotating-head, direction-finding antenna 
and associated receivers. 


sion of I wo Jima, the tactical doctrine for the 
use of RCM against enemy airborne radar was 
advanced. Installation and training programs 
had progressed to the point where a substantial 
RCM effort could, if necessary, be concentrated 
at Iwo Jima to assist in protecting the large 
number of ships which would be required. Ac- 
cordingly, operational orders were prepared in 


340 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


which intercept guards were established from 
40 to 3,400 me, in accordance with ^‘Cent. Com. 
Two, Annex B.” Specific jamming orders were 
not written but left to the discretion of the 
OTC. Fully aware of the threat from enemy 
airborne radar attacks, however, several LCIG- 
RCM as well as newly complete radar and RCM 
picket vessels were assigned to the Amphibious 
Assault Forces, Task Force 52, in addition to 
its complement of other RCM-equipped vessels. 

Beginning on February 16, 1945, the initial 
phases of the attack proceeded without inter- 
ference from radar-equipped enemy aircraft. It 
was not until the night of February 19, D-Day, 
that the first Air Mark VI signal, with charac- 
teristics of 152/1,000/5, was intercepted on the 
TDY rotating antenna aboard the USS Estes, 
AGC-12. Jamming was initiated and the bogie 
secured his radar. From this and subsequent 
action, it was evident that the antijamming les- 
sons learned by the Japanese in the Philippine 
invasion had not been widely disseminated. In 
striking contrast, U. S. naval forces were in an 
excellent position to put their previous experi- 
ence to good use. 

Approximately six radar and RCM pickets 
were stationed in the area, at distances of 10 to 
50 miles from the island. Adequate warning 
necessary for the tuning of spot- jamming or 
barrage- jamming transmitters was easily ob- 
tained. 

Protection for the vessels in the transport 
area was afforded by both the RCM-equipped 
vessels of the force and the ten or so specially 
prepared LCIG-RCM. Before the landing had 
been effected, it was customary for these latter 
vessels to approach close to the beach under 
the cover of darkness and deliver a rocket bar- 
rage. When necessary, the pretuned AN/SPT-4's 
which they carried were called into action as 
barrage jammers for Air Mark VI signals. 

The enemy’s reaction to jamming was, usu- 
ally, that of turning off his radar, orbiting, and 
then returning to base. In direct contrast to 
experience in the Philippine operations, enemy 
air attacks in the transport area at I wo Jima 
were not often pressed home with suicidal fury. 
When the enemy radar was jammed its oper- 
ator appeared to conclude that his mission could 
not be carried out and thus returned to base 


with a somewhat dubious explanation for his 
action. The possibility that the jamming signal 
or signals might be used by an enemy radar 
operator to guide his aircraft to a suitable tar- 
get seems to have been almost entirely over- 
looked. Naval records, up to this time, indicate 
only one incident in which this tactic might 
have been attempted. Off Iwo Jima on March 
20, 1945, the USS Indianapolis, CA-35, inter- 
cepted and jammed a signal of the character- 
istic 147/750/10 which had the same bearing 
as an enemy raid under scrutiny on the ship’s 
SK. The raid closed from 2,200 to 2,223K, at 
which time it was jammed with a TDY trans- 
mitter. At 2,237K, 4 min later, the raid broke 
its direct line of approach and began to orbit. 
After orbiting for some minutes the enemy air- 
craft started to close again, along the same 
course that it had previously followed. This 
course was most likely chosen because it was 
the one last followed, but conceivably it might 
have been an attempt to home on the source of 
the jamming signal. At any rate the enemy 
raid, consisting of two aircraft, was immedi- 
ately engaged by the screening forces and 
splashed. The total number of radar-equipped 
enemy aircraft which attacked U. S. vessels in 
the region of Iwo Jima is difficult to estimate 
but is thought to be in the neighborhood of 10 
to 15. One observer aboard the USS Estes, 
AGC-12, believes that not more than ten such 
attacks took place between February 16 and 
March 4, 1945. Later the RCM control officer 
was stationed aboard the USS Eldorado, and 
the USS Auburn, and it is believed that some- 
what fewer attacks took place during the en- 
suing period in which the island was secured. 

In the time between the invasion of Iwo Jima 
and that of Okinawa numerous diversionary 
strikes were undertaken against widely sepa- 
rated objectives. Jamming transmitters were 
called into action in almost every instance when 
U. S. naval forces came under attack by enemy 
Mark VI radars. The general conclusion at the 
end of this period was unanimous approval of 
RCM tactics and equipment. From naval rec- 
ords it is not difficult to discern the basis of 
such a conclusion. For example, the action re- 
port of the USS Vincennes in the period of 
March 20 to April 15, 1945, reads : 


NAVAL RADAR COUNTERMEASURES 


341 


Date 

Time 

Location 

3/20 

2150K 

200 mi. S. East Kyushu 

3/20 

2215K 

200 mi. S. East Kyushu 

3/21 

1135K 

115 mi. S. East Okinawa 

4/12 

2037K 

60 mi. East Okinawa 

4/14 

1940K 

95 mi. East Okinawa 

4/15 

0043K 

100 mi. N. East Okinawa 


In planning Operation Iceberg, the invasion 
of the Okinawa-Gunto, RCM operational orders 
were prepared for the various forces of the 
Fifth Fleet. For the first time, such orders in- 
cluded intercept guards and both spot- and 
barrage- jamming plans. Intercept guards were 
arranged to cover all frequencies from 40 to 
3,400 me, but the jamming plans were limited 
to the Japanese airborne bands, with the em- 
phasis on 150 to 160 me, for the Air Mark VI 
radar. RCM equipment to carry out these plans 
was to be available in quantity. Approximately 
six AGC’s with their elaborate RCM installa- 
tions were assigned to the operation. Some 30 
LCIG-RCM with Rug and Dina transmitters 
and amplifiers were especially prepared for 
barrage jamming proposed in the transport 
area. In addition to these specially prepared 
vessels, the normal RCM installation of the 
assigned fleet units was available. All actual 
RCM operations for this large group of vessels 
followed the general plan of PAC-70 (B). 

As the operation got under way on March 26, 
enemy air attacks were numerous from the 
beginning. It is interesting to note, however, 
that the great proportion of the attacks were 
not assisted by airborne radar. The enemy 
either did not have a large quantity of opera- 
tional radar or he deliberately ordered that it 
not be used. For example, the RCM control offi- 
cer aboard the USS Estes reports : 

1. The only airborne intercepts obtained during the 
nights of L — 7 to L + 4 day were signals from the 
Mark VI radar (153/1000/8). Although bogies were 
within the vicinity of Okinawa almost constantly during 
these nights few such intercepts were obtained. From a 
total of 36 raids in the above period, Mark VI inter- 
cepts were obtained on three of them. Signals were 
picked up when the bogies were 80-90 miles away and 
were received intermittently while they closed. No 
signals were heard after the enemy aircraft approached 
to within 15-4 miles of Okinawa. Look-through periods 


Result 

Bogey turned away during jamming, but picket 
was firing. 

Bogey turned away during jamming, no vessel 
firing. 

Bogey turned away at 8 mi. when jammed. 

Two bandits turned away at 8 mi. when jammed. 
Bogey turned away at 7 mi. when jammed. 

Bogey jammed at the same time that it was taken 
under fire by picket. He turned away and was later 
splashed by a VF(N). 

varied anywhere from ten seconds to six minutes, while 
the bogies were approaching. Periods between looks, 
varied in a similar manner. Such tactics indicated the 
enemy might be using his radar to find and then home 
on the island of Okinawa. Undoubtedly, he was pre- 
viously informed of the fact that we could jam his set. 

2. After L + 4 day Mark VI signals were heard just 
as infrequently although the tempo of the air raid ran 
about the same. 

As a rough estimate one observer 'who was 
aboard the same vessel, the USS Estes, believes 
that in the 30-day period following L-day, when 
the troops first went ashore at Okinawa, ap- 
proximately 15 Air Mark VI signals were inter- 
cepted and jammed. After this, as time went 
on the number of intercepts decreased. With a 
decrease in the total number of intercepts, new 
types of enemy ASV radar made their appear- 
ance. For instance, in the early morning of 
April 7, 1945, an airborne signal with the char- 
acteristics 210/750-1,000/15 was obtained. Pos- 
sibly this intercept indicates use of the Japanese 
Army Taki Model 1. Because its frequency was 
in the same band as U. S. air-search raiders, the 
SC and SK, jamming was not attempted. 

The exact manner in which the enemy had 
been directed to use his ASV-type radar is, even 
now, not known with certainty. It seems likely 
that after the initial days of the operation in- 
structions were issued to use airborne radar at 
infrequent intervals in order to decrease the 
probability of intercept and successful jamming 
by U. S. forces. Although the Air Mark VI was 
originally intended for locating surface vessels 
it was probably used sometimes as a naviga- 
tional device to guide attacking aircraft to the 
general area of an island. Furthermore there 
is a possibility that the receiver portion of the 
Air Mark VI was used to home on 

1. Allied v-h-f voice transmissions. 

2. Allied IFF. 


342 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


3. Enemy shore-based radars such as the 
Mark I Model 3. 

None of these possibilities was ever definitely 
proved, however, and the exact navigational or 
homing procedures used by the enemy are un- 
certain. 

Of particular value in interception of enemy 
airborne radar was the high-gain, rotating, di- 
rectional antenna, familiarly known as the 
“TDY rotating antenna.’' The RC^ control 
officer aboard the USS Estes singles out this 
particular item for comment. 

TDY rotating antenna has been of great value in 
intercepting enemy signals. Signals have been con- 
sistently received from enemy planes reported (by 
radar) at distances from 80 to greater than 100 miles. 
At these distances no signals were received on a dipole 
antenna. For example, while en route to Okinawa, RCM 
reported an airborne radar signal 153/1000/8 on a bear- 
ing of about 060T. One of the radar picket ships in the 
screen reported an enemy plane on this same bearing. 
From the approximate speed of the plane it was found 
that this signal when first intercepted was at a distance 
of 110 miles. When the plane was disappearing through 
a radar fade we were able to follow him with the TDY 
antenna; by dead reckoning an idea of his movements 
was obtained, until he again reappeared on the radar. 

Thus ends the report on the role played by 
ship-borne countermeasures against enemy air- 
borne radar in the invasion of Okinawa. As in 
any countermeasures operation the determina- 
tion of its success in concrete terms is extremely 
difficult. It will be obvious, though, that numer- 
ous night air attacks were either prevented or 
made less effective. In spite of the fact that 
electronic jamming will not stop a Kamikaze 
pilot, RCM assisted in preventing the large 
number of fleet units lost at Okinawa from 
being larger still. 

Miscellaneous 

Since this chapter is principally concerned 
with the operational use of radar countermeas- 
ures in World War II, detailed discussion of 
communication countermeasures, guided missile 
countermeasures, and AJ techniques has been 
avoided. Pacific naval operations, however, in- 
volved considerable effort in each of these fields. 
For these reasons, a brief reference indicating 
the status and plans in these fields as of April 
22, 1945, is included below. 


Communication Countermeasures 

PAC-70 (B) directs that 

fleet commanders, the OTC, and landing force com- 
manders having qualified personnel will intercept enemy 
circuits and take action in tactical situations. Ordinarily 
jamming has less military value than the information 
which may be obtained from interception. 

The approved type allowances of communication 
countermeasures equipment calls for radio intercept and 
jamming equipment of AGC’s and fleet and major task 
force flagships only. Communication countermeasures 
activities in the Pacific Ocean Areas have been purpose- 
fully limited to keep radio jamming and deception 
operations under the direction, supervision, and control 



Figure 8. Typical installation on the aftermast 
of a destroyer of DBM-1, high- and low-fre- 
quency, rotating-head, direction-finding antennas. 

of those echelon commanders who at the same time 
have the immediate services of the communication secu- 
rity and radio intelligence organizations. 

Radar Antijamming 

PAC-70 (B) directs all commands to insure 

that radar and CIC personnel receive intensive training 
in radar anti-jamming. Maximum use of AJ techniques 
and equipments shall be made in an endeavor to combat 


RCM IN THE U. S. AIR FORCES 


343 


any enemy countermeasures and to read through any 
interference caused by friendly jamming operation. 

Guided Missile Countermeasures 

To date (April 22, 1945) there has been no GMCM 
activity in the Pacific Ocean Areas because the Japa- 
nese have substituted the human mind and body for 
the more conventional “radio-control” features nor- 
mally favored by other nations for guided missiles 
work. There is, however, close liaison between the 
Japanese and Germans in the electronic field and this 
fact, coupled with the acute pilot-shortage which might 
be caused by such costly attrition as that occasioned by 
suicide tactics, may force the Japanese into an attempt 
to follow the German guided missiles program. To pre- 
pare for such an eventuality three GMCM Investiga- 
tional Groups, composed of GMCM personnel from the 
European Theater who have received additional re- 
fresher training at SPS, have been formed and assigned 
to ComDesPac. These groups, one of which is already 
operating, accompany various task forces and main- 
tain a continual search with highly-specialized equip- 
ment for any guided missiles control signals, recording 
for analysis and reporting all unidentified or suspicious 
intercepts. 

Ten destroyer escorts are being fitted with GMCM 
intercept and jamming equipment as a further standby 
measure. If it becomes necessary to combat a full-scale 
Japanese guided missiles program, ten more GMCM 
Investigational Groups will be requested from CNO and 
assigned to these ten DE’s. In addition, a supply of 
GMCM jamming and monitoring equipment will be 
maintained in various material pools in the Pacific 
Ocean Areas to be used for immediate installations in 
major combatant ships if necessity arises. “Crash” 
instruction will be conducted, in this event, both at 
SPS and at the Pacific Fleet Radar Center to provide 
radio personnel from the Fleet trained to operate this 
GMCM equipment. 

1- 6 rcM in the u. s. air forces 

15.6.1 Operational Problem 

There were marked differences between the 
RCM program in the Pacific Theaters of Oper- 
ations and those in the European and Medi- 
terranean Theaters of Operations, the most 
outstanding being the infinitely greater recon- 
naissance problem encountered in the Pacific. 
U. S. forces in the ETO and MTO were indeed 
fortunate in having available all the information 
of German radar operations and developments 
that the British had been gathering since 1939. 
The line of approach to the planning of equip- 
ment requirements and operational tactics was 
at least partially indicated. This was not so in 


the Pacific Theaters of Operations. It was a 
long job, requiring many months of intensive 
RCM reconnaissance work, to establish the 
types and functions of radars being used by the 
Japanese. Merely the effect of the distances be- 
tween the various areas within the theater re- 
quired that complete reconnaissance of each 
area be accomplished before offensive opera- 
tions in that area could be undertaken. Since 
the progress in the Pacific was from the newly 
won outlying areas toward the well-established 
inner defenses of the Japanese home islands, 
the best defenses were not encountered until 
the 20th bomber Command began operations in 
June 1944. This required that offensive counter- 
measures, where necessary, be initiated almost 
immediately after the operational use of GL 
and SLC radar had been definitely established 
and its characteristics known. 

RCM operations in the Pacific were different 
from those in Europe in another respect. The 
similarity of RCM problems in the ETO and 
MTO made the same tactics feasible in both 
places, whereas in the Pacific major emphasis 
on different phases of RCM activities appeared 
in the different parts of the theater. For in- 
stance, in the Southwest Pacific Area, consider- 
able emphasis was placed on attacking enemy 
radars (‘‘radar busting”) and deception activ- 
ities. Because of the small number of radars 
covering a given area, it was possible to gain 
a great tactical advantage by making one of 
them useless by one means or the other. On the 
other hand, in the Nanpo Shoto and Nansei 
Shoto island chains radar busting and decep- 
tions would have been much less fruitful be- 
cause of the high density of radars on all fre- 
quencies and the prevalence of radar-equipped 
picket boats. Gun-laying radar was never found 
in any quantity in the Northern Pacific and 
CBI areas, and no jamming equipment was 
ever employed. In the Philippines and Formosa, 
GL and SLC radar appeared in small quantity, 
and over the Japanese home islands consider- 
ably greater numbers of gun-laying and/or 
searchlight-control radars appeared, both areas 
requiring the use of offensive RCM. It should 
be reiterated that the Japanese GL/SLC radar 
was never good enough to constitute a serious 
threat to the success of operations. 


344 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


A few attempts were made to reduce fighter 
opposition by deception and evasion both in the 
Southwest Pacific and over the Japanese home 
islands, but no wide-scale effort to avoid fight- 
ers, such as was necessary at one time in the 
ETO, was ever attempted in the Pacific. Fighter 


different. Instead of bundles containing a large 
number of small dipoles cut to the frequencies 
of the enemy radar, the type of Window em- 
ployed in the Pacific was in the form of a long 
aluminum strip called Rope. This consisted of 
a ribbon of aluminum about 1/2 in. wide and 



Figure 9. Japanese radar-coverage map prepared from the search results of aircraft, surface vessels, 
and submarines. Coverage of early-warning, gun-laying, and searchlight-control radar is indicated. 


opposition in the spring and summer of 1945 
was never great. 

Capabilities and Limitations of the 
RCM Available 

In the Pacific Theater, as in the European 
Theater of Operations, the two main lines of 
attack against the enemy radar involved the 
use of Window and electronic jammers. Because 
of the differences between the Japanese and 
German radars, however, the type of Window 
and electronic jamming employed had to be 


400 ft long, tied to a nylon leader about 15 ft 
long. At the end of the nylon ribbon, a small 
chute or a cardboard tab was attached. When 
the Rope was thrown out of the plane, the small 
parachute or the cardboard tab was caught in 
the slip stream and the ribbon unwound itself. 
Rope completely unwound falls at the rate of 
about 600 ft a minute. Depending upon the air- 
craft and upon the frequencies of the enemy 
radar against which it works, a bundle con- 
taining three rolls of Rope represented an echo 
comparable, if not equal, to the echo given by 
a heavy bomber. Since Rope is an “untuned’^ 
reflector, it was effective against all Japanese 



RCM IN THE U. S. AIR FORCES 


345 


radars simultaneously, especially since the ma- 
jority of enemy radars operated below 200 me. 
Window, employing bundles of small dipoles, 
was used only to a very limited extent. 

Electronic jamming employed transmitters 
based on the same fundamental principle of 
operation as those used in Europe, but the dif- 
ferent frequencies involved made new sets nec- 
essary. These sets had to cover the frequency 
band from 70 to about 220 me. No one set was 
available which was capable of covering the 
whole enemy band. For this reason, three types 
of transmitters were employed in the Pacific 
Theater: APT-1 (Dina) ; APQ-2 (Rug) ; and 
ARQ-8 (1-f Dina). Without going into the tech- 
nical differences between these three sets, it 
might be mentioned that the latter, the ARQ-8, 
was an 1-f set capable of covering frequencies 
from 50 to about 100 me; that Dina could be 
employed above 100 me ; and that Rug had to be 
modified to cover frequencies below 200 me. 

Window 

The observation made in the paragraph en- 
titled “Chaff’ under Section 14.5.2 in the pre- 
vious chapter can be extended to Rope. Some 
differences exist, however, because of the differ- 
ent type of operation, the different types of 
formation, and the different types of radar. 
When Rope was dispensed by a formation of 
tactical aircraft, the full protection that Rope 
could give to the formation flying near or 
within a Rope trail was not available. The rea- 
son for this was, of course, that very seldom 
did more than one formation attack the same 
target within an interval of time short enough 
to make the full protection of Rope available 
to the trailing formations. In this case, the 
effect of Rope was one of introducing confusion 
into the enemy’s radar picture so as to make it 
difficult for the operator to locate the target 
and track it continuously. The use of Rope by 
the B-29’s was very similar to the use of Chaff 
by the 8th and 15th Air Forces. B-29’s flew in 
formations comparable in size to the formations 
flown in Europe. It must be added, however, 
that B-29’s also flew night missions with single 
aircraft and in this case, more than for day- 
light formation flights, it was difficult for the 
radar operator to locate the Window trail and 


to track their leading edges except for the 
period when the first aircraft were flying over 
the target area. 

In Europe, the RAF repeatedly used Chaff 
as a means of deception. The planes of the 
Bomber Command dropped Chaff during their 
whole course at a rate much slower than the 
one employed by the American Air Forces. 
Whereas the American Air Forces in Europe 
dropped Chaff only on or near the target area, 
the RAF laid trails of Chaff during the whole 
penetration course and part of the withdrawal. 
The Bomber Command employed small forces 
dropping large amounts of Chaff to simulate 
attacks where no major attack was going to 
take place, or at a time different from the real 
one. Tactics similar to these were occasionally 
employed in the Pacific Theater by several of 
the air forces. The effectiveness of these decep- 
tion missions cannot be evaluated, in general, 
but some information is available and will be 
discussed in detail in the following sections of 
this report which refer to the activities of the 
particular air forces. 

Rope is particularly useful as a deception 
measure because it covers a wide band of fre- 
quencies. Especially against an enemy whose 
radar network had to cover very wide areas 
and whose approaches were always from the 
sea, deception maneuvers appeared attractive. 
However, no deception maneuvers of the order 
of magnitude employed in Europe in the inva- 
sion of Normandy or of southern France were 
attempted. 

The Japanese did not develop any AJ device 
comparable to the ones developed by the Ger- 
mans as a defense against the Allied use of 
Window. For this reason, despite the fact that 
at the time of the writing of this report no 
direct intelligence is available on the effective- 
ness of Allied RCM on the Japanese radar, it 
appears likely that Rope was effective in throw- 
ing the enemy radar off balance. Operational 
reports from both strategic and tactical air 
forces reported successful evasion of enemy 
searchlights by Allied aircraft. 

Electronic Jamming 

The two types of electronic jamming de- 
scribed and discussed in the previous chapter 


346 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


applied also in the Pacific Theater. The advan- 
tages and disadvantages of spot and barrage 
jamming were the same in the two theaters. 
It must be mentioned, however, that, for a 
tactical air force which attacked a target with 
only one or two radars, it would have been very 
uneconomical to employ a barrage type of jam- 
ming. For this reason, spot jamming was em- 
ployed in practically all the tactical air forces. 
In some cases, the knowledge of the enemy 
radar was good enough to enable the jammers 
to be pretuned on the ground to the frequency 
or frequencies that the dangerous radar or 
radars were known to have. 

In the case of the 21st Bomber Command, on 
the contrary, the analogy with European The- 
aters was practically complete, and barrage 
jamming and spot jamming were used in com- 
bination in a way very similar to the one 
already described with the 8th and 15th Air 
Forces. The operations of the 21st Bomber 
Command will be described later in detail. It 
must be mentioned here, however, that the 
weaknesses of the Japanese radar were such as 
to make it possible to employ in the Pacific a 
method which had been used by the RAF 
against the German ground-controlled-intercep- 
tion radar but which could not be duplicated in 
Europe by the AAF against the German gun- 
laying radar. By this it is meant that the 21st 
Bomber Command found it possible to use spe- 
cial aircraft flying over the target area, contin- 
uously jamming these enemy radar sets and 
dropping Rope. This was done during night 
operations only; the reason why this could not 
be done in Europe was that the number of 
special aircraft necessary to jam the German 
Wurzburg would have been prohibitive because 
of the narrow beamwidth and wide frequency 
spread of this radar set. The use of these special 
aircraft, called Porcupines, will be discussed in 
detail later. 

Except for the observations made above, all 
the considerations listed in the previous chapter 
in the paragraph on ‘‘Carpets” under Section 
14.5.2 about the relative merits of barrage and 
spot jamming, training of spot- jamming oper- 
ators, danger of the enemy DF-ing on Allied 
jammers as a means of laying its guns — all 
apply to the Pacific Theater unchanged. 


15.6.3 Operational Use of RCM in 
Northern Pacific Theater 

Search and Investigation 

The Northern Pacific Theater was the first 
theater of operations in which any RCM activ- 
ity took place. After the Japanese were forcibly 
removed from the Aleutians, the theater activ- 
ities were very much reduced in scope. During 
both the active and inactive phases of opera- 
tions, the RCM work was limited to search and 
investigation. 

In the fall of 1942, photo-reconnaissance of 
the Kiska area revealed what might be a radar 
station. It was felt that an RCM reconnaissance 
aircraft would be valuable for confirming this. 
As a result, an offer of a Ferret was made to 
the 11th Air Force, and, on the advice of the 
Operational Analysis Section, the Ferret was 
requested by the theater. Thus, work on Fer- 
ret I was initiated. The B-24D was outfitted at 
East Boston and at Wright Field in December 

1942 under the supervision of RRL personnel. 
The Ferret was equipped with the newest re- 
connaissance equipment available at that time. 
No DF antennas were available, but stubs were 
mounted on the nose for left-right homing. 

Ferret I arrived in the theater in January 

1943 and began operation out of Adak. Two 
specially trained RCM officers came to the the- 
ater with Ferret I and operated the reconnais- 
sance equipment on search missions. The Ferret 
was also used for weather and radar reconnais- 
sance work. From January to March, missions 
were flown west from Adak to Kiska, Attu, and 
Paramushiru. Two Mark I Model 1 radars on 
Kiska were located roughly about 500 ft above 
Kiska Harbor. The Ferret proceeded to log 
the characteristics and plot the coverage of the 
two radars. After March, Ferret I made occa- 
sional flights to check periodically on the radars 
on Kiska, but the majority of its time was 
spent in weather reconnaissance work. It was 
called into service for RCM reconnaissance 
again shortly before the invasion of Kiska in 
August 1943, when it was used to augment the 
search activities of Beaver I. During these 
searches, a 300-mc signal was logged, which 
later proved to be spurious, and an APQ-2 was 


RCM IN THE U. S. AIR FORCES 


347 


rushed to the theater in preparation for jam- 
ming this radar if necessary. 

Eleventh Air Force RCM activity was dor- 
mant until the first part of 1945, when a new 
Ferret I arrived in the theater. This Ferret was 
attached to the 40th Bomb Squadron (H) and 
flew its first mission on January 20, 1945. This 
Ferret was equipped with the latest reconnais- 
sance equipment. Routine searches were made 
in the vicinity of Paramushiru and the northern 
Kuril Islands and the same type of EW radars 
encountered in other theaters were heard. On 
April 18, 1945, in the vicinity of Shimusu and 
Paramushiru, Ferret I made its first intercept 
of a radar of Mark TA Model 3 characteristics. 
This radar was presumed to be at the Kataoka 
Naval Base and was associated with flak 
through undercast. However, the flak was in- 
accurate and did not constitute a problem. Fur- 
ther missions mapped all the radars in the area, 
but flak, and especially flak against unseen tar- 
gets, was never accurate enough to cause con- 
cern. 


10.6.4 Operational Use of RCM in the 
Southwest Pacific Theater 

RCM Organization 

The organization initially responsible for all 
RCM in the Southwest Pacific Area was Sec- 
tion 22, an Allied inter-Service organization in 
General Headquarters [GHQ]. It consisted of 
a headquarters and a number of “field units.'’ 
The headquarters planned and coordinated 
RCM activities, analyzed and disseminated RCM 
intelligence, and requisitioned and assigned 
RCM personnel and equipment. The field units, 
as the name implies, gathered data and either 
carried out, or cooperated in, the execution of 
RCM plans. This arrangement prevailed dur- 
ing what might be called the investigational 
period of SWPA RCM, lasting from late 1943 
to, roughly speaking, the beginning of 1945. 
In this period, Japanese radar in the theater 
grew from insignificance to the point where it 
became a threat to operations. Through the 
activities of Section 22 in this period, the Allies 
were able to keep informed of Japanese radar 


developments and found themselves at least 
partially prepared to take measures against 
Japanese radar when they became desirable. 

As time went on, the war in the SWPA grew 
on both sides in scope and modernity, and em- 
phasis in RCM gradually shifted from intelli- 
gence to jamming and physical attack. It was 
inevitable that in the short-range planning of 
RCM activities the field units should more and 
more work directly with the operational com- 
mands involved (such as the Seventh Fleet and 
the Fifth Air Force) , and the field units gradu- 
ally assumed a free hand in this respect. How- 
ever, Section 22 retained its other prerogatives 
— long-range RCM planning, including supply 
of equipment and personnel, and intelligence 
coordination. 

As of May 1, 1945, Section 22 relinquished 
operational control of Army Air Force RCM to 
the Far East Air Forces [FEAF] and of naval 
RCM to the 7th Fleet. With this transfer, the 
field units which had been working with the 
Air Forces and Navy were dissolved, and their 
personnel and equipment were turned over to 
the respective commands. Day to day operations 
continued just as before. Section 22 remained 
as the central RCM intelligence organization 
of the theater and continued to control Army 
Ground Force RCM, which was principally con- 
cerned with communications. 

Search and Intelligence 

Two sources of information on Japanese 
radar were available: intelligence reports and 
intercepts by search equipment. The former 
originated chiefly with captured material and 
prisoner of war interrogations. As Allied forces 
advanced, more and more Japanese equipment 
and documents were captured. The information 
gained was invaluable. Even more benefit could 
have been derived from the booty had there 
been in the theater a well-equipped group of 
scientists to perform detailed analyses. In this 
way, the results could have been used immedi- 
ately. 

The first attempts at carrying out radar 
search were made from strike aircraft, sub- 
marines, and motor torpedo boats. This type 
of search grew in scope as World War II ad- 
vanced, and from the middle of 1944 on it pro- 


348 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


vided much reliable data on Japanese radar. 
It was handicapped in the beginning by the 
absence of DF-ing facilities (and the naviga- 
tional aids required for their effective use) and 
by the fact that the only receiver available had 
spurious responses so that the number of radar 
frequencies reported considerably exceeded the 
number later found to be employed by the 
enemy. Nevertheless, during 1943 some cover- 
age of the areas immediately north and west 
of Australia was obtained, and a limited cover- 
age of certain regions in the Philippines, China 
Sea, and Malay Peninsula was accomplished by 
submarine. 

The need for special radar reconnaissance 
aircraft. Ferrets, became increasingly appar- 
ent. Even with the best of equipment, strike 
aircraft have some inevitable limitations. They 
can only cover the areas swept out by strikes 
and so fail to give advance information for use 
in planning future activities. They are not free 
to navigate in such a way as to obtain the best 
RCM information; and the amount of special 
gear that they can carry is limited. Thus, ade- 
quate coverage of Japanese air-warning radar 
could only be provided by Ferrets. By January 
1944, two USAAF B-24 Ferrets, which had 
been fitted out in the United States, were oper- 
ating from New Guinea bases. During the next 
2 months, 32 Ferret missions were completed 
in the Bismarck Sea area. Specific searches 
were made around the Admiralty Islands and 
Hollandia, New Guinea, in preparation for the 
forthcoming Allied landings. 

By July 1944, the investigation of the North- 
west Pacific Area (i.e., a region bounded by 
Borneo, Java, Australia, and New Guinea) was 
completed. The acquisition of Owi made it pos- 
sible to obtain coverage farther north, so that 
Morotai and the Palaus were well surveyed be- 
fore the landings there (September 15, 1944). 
The next step was the Philippines, and cover- 
age up to Manila was provided. A few days 
before the Leyte invasion (October 20, 1944), 
existence of a radar on Suluan Island, com- 
manding the entrance to Leyte Gulf, was con- 
firmed, and as a result a party of Rangers was 
sent in to destroy this radar at the start of the 
invasion. 

During one of the Philippine flights a Ferret 


made the first unequivocal intercept of Japa- 
nese ship-borne radar by obtaining direction- 
finding bearings which were coincident with a 
ship plot on the SCR-717. 

In the winter of 1944-45, the two Ferrets 
began to show signs of wear. Nevertheless, the 
coverage of the Philippines was completed and 
some Formosa data were obtained. One replace- 
ment Ferret finally arrived in February 1945. 
The coverage of Formosa was completed, and 
the Asiatic coast, from Saigon to Shanghai, was 
mapped out. A second replacement Ferret ar- 
rived in April. A number of flights to Kyushu 
were also made before World War II ended. 

There were some other aircraft in the theater 
assigned to full-time radar investigation. A 
Navy Catalina under the operational control of 
Section 22 was fitted with search gear in the 
theater and began operations in May 1944. In 
the absence of a DF antenna, a pair of sym- 
metrically placed cones was used to DF by hom- 
ing. In this way, a number of EW stations in 
New Guinea, Halmahera, and the Philippines 
were located. During the second battle of the 
Philippines (October 26, 1944), the PBY de- 
tected and located by its RCM gear a Japanese 
task force moving through the Camotes Sea and 
reported it at once. Delay in retransmission of 
the message prevented our naval forces from 
using this vital information. This PBY was 
later replaced by another, also fitted out in the 
theater, whose RCM complement rivaled those 
of the Ferrets. It included an APA-24 DF an- 
tenna. This Catalina was particularly valuable 
at the height of the Philippine campaign, when 
the two B-24 Ferrets were operating on a re- 
duced basis. 

Another Ferret was the so-called Armed Fer- 
ret of the Thirteenth Air Force, a B-24 fitted 
out in the theater, early in 1945, with a great 
variety of RCM equipment. It had, in addition 
to the normal search gear, homing equipment 
for use in radar busting, and jamming antennas. 
The arrangement of the equipment permitted 
use of the plane in normal strikes with full bomb 
load as well as on lone reconnaissance. The per- 
sonnel of this plane worked out a new technique 
of locating radars using a camera. This photo- 
graphic technique, which was quite successful, 
was obviously usable only under conditions of 


RCM IN THE U. S. AIR FORCES 


349 


overwhelming air superiority, when unescorted 
daylight flights were permissible. 

In view of the necessity, pointed out below, of 
intercept both in strikes and on special recon- 
naissance flights, the Armed Ferret appears to 
be closest to the ideal RCM installation. It com- 
bines the advantages of a standard combat 
plane with those of a flying laboratory. 

Concurrently with all this special reconnais- 
sance, search was being carried out from strike 
planes. It was realized that only by search dur- 
ing strikes could it be determined how the Jap- 
anese used their radar against enemy aircraft 
and whether they had GL, SLC, or GCI in op- 
eration. For this reason, before strike planes 
were adequately equipped with search gear, the 
Ferrets accompanied several strike missions. In 
only one instance was any short-range radar 
heard, a probable GL or SLC radar at Balik- 
papan, but it was discovered that some EW 
radars came on the air only when a strike was 
under way. Thus, search coordinated with 
strikes was required even for complete coverage 
of early-warning radars alone. 

By the middle of 1944, a fair supply of 
APR-l’s and APA-6 pulse analyzers was on 
hand. The 380th and 90th Bomb Groups (H) of 
the 5th Air Force, which engaged in daylight 
strategic bombing, flew at least one B-24 
equipped with receiver and pulse analyzer on 
each strike. On January 13, 1945, a 200-mc high 
prf signal was heard tracking the formation in 
the target area. Search now became more than 
a precautionary measure, and all four B-24 
groups of the Fifth Air Force were soon carry- 
ing intercept receivers on their missions to tar- 
gets with heavy flak. Consistent use of both 200- 
mc and 79-mc GL radars by the Japanese on 
Formosa was revealed, and 200-mc GL radars 
were also located at Ambon and Saigon. 

January also saw the beginning of H2X op- 
erations in the theater. The H2X-equipped 
planes were first used simply as lone night 
bombers. One of them had some intercept gear 
and was able to check on the use of radar for 
SLC in Formosa. As anticipated from the 
October 1944 Balikpapan intercepts and from 
intelligence 200-mc SLC radar was used, and be- 
ginning on January 22 diversionary tactics were 
introduced as a countermeasure. 


Another class of strike plane was the radar- 
equipped B-24’s that engaged in antishipping 
patrols over the vast expanse of the theater. 
Outstanding in RCM was the 868th Squadron of 
the 13th Air Force, which started intercept 
work in the middle of 1944. In October 1944, a 
B-24 of this squadron confirmed the use for 
SLC of a 200-mc radar at Balikpapan that had 
been heard previously by a Ferret, and Chaff 
(CHB-1) was used against it, with undeter- 
mined effect. In this same month, some homing 
antennas were constructed in the squadron and 
installed; and Japanese radars were designated 
as permissible secondary targets for this squad- 
ron. As time went on, and the number of lucra- 
tive shipping targets diminished, the detection, 
location, and destruction of Japanese radars be- 
came a major activity. An example of the “per- 
fect” RCM mission occurred on November 3, 
1944, when one of these B-24’s intercepted, 
homed on, then photographed, and finally 
bombed and strafed an enemy radar on Sibago 
Island (Sulu Archipelago). 

Mention should also be made of the B-25 
“radar busters” of the Thirteenth and Fifth 
Air Forces, which located radars as well as at- 
tacked them. 

RCM AGAINST Early-Warning Radar 

This section and the following one are con- 
cerned with the use made of the information 
gathered on Japanese radar, as described in the 
preceding section. 

The only practical countermeasures against 
EW radar were evasion, deception, and destruc- 
tion. 

Location of the radars made it possible to 
estimate their heights above the water (almost 
all the radars were coastal) ; from their known 
capabilities, the ranges could then be calculated 
at which, under average conditions, planes at 
various heights could be detected and the shad- 
ows due to terrain features could be estimated. 
Coverage charts, showing these contours of de- 
tection, were issued regularly and were used in 
various ways : to lay out the courses of bombing 
missions that lacked fighter escort; to deter- 
mine the courses and altitudes to be used by 
mine-laying planes, as in the mining of Balik- 
papan Harbor by Catalinas in the summer of 


350 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


1944; to do the same for the Air-Sea Rescue 
Catalinas that picked up flyers from enemy ter- 
ritory and carried supplies to guerrillas ; and to 
plan low-altitude attacks on the radars them- 
selves. The charts were also used to define areas 
in which IFF silence was to be maintained. This 
was necessitated by the fact that some of the 
Japanese Mark I Model 3 radars operated in the 
frequency range of Allied IFF. The consequent 
triggering of the IFF would increase the range 
of the enemy radar. 

Deception tactics were used in connection 
with a number of special operations. The wide 
dispersion of Japanese radars in the theater 
made it possible to carry out these deceptions 
with the very limited means available, though 
the slowness of the enemy in reacting to any- 
thing out of the ordinary and the lack of coordi- 
nation between his various headquarters tended 
to reduce the operational value of any decep- 
tion. In coordination with the Leyte landing 
(October 20, 1944), the two Ferrets and an ad- 
ditional B-24 used Dinas and Chaff to simulate 
the screening of air operations against Min- 
danao, with uncertain results. 

A second try at deception was made on Janu- 
ary 4-5, 1945, in connection with the landing on 
Luzon 4 days later. Here the attempt was to 
simulate the approach toward Legaspi of a 
naval bombardment force with air cover. The 
limited naval and air facilities in the theater 
made it necessary to attempt the job with only 
one plane, one of the Ferrets, which circled 
about, advancing at an average speed of 20 k, 
all the time dropping Rqpe. Just how the Japa- 
nese interpreted their radar plots is not known. 

An example of a mission where clear-cut suc- 
cess was obtained is an operation undertaken 
by the Thirteenth Air Force early in 1945. Here 
use was made of the Japanese practice of shut- 
ting down when an unidentified aircraft closed 
to within about 5 miles. It was desired to bomb 
an airfield on Halmahera, all the approaches to 
which were covered by a particular EW radar. 
A “heckling’^ plane made passes at this radar 
for about an hour, causing it to stay off the air ; 
meanwhile, the strike reached the target unde- 
tected and did not receive any fire till it was on 
the way out. Several other successful heckling 
operations were carried out later. 


Physical attack on enemy EW radars was a 
major activity during the last year of the war in 
the SWPA. The dispersion of the Japanese posi- 
tions, and their bad supply and training situa- 
tion, made the Japanese very vulnerable to this 
kind of countermeasure. In a number of cases 
the radar busting had immediate tactical value. 
Allied “leapfrogging’’ had left the Japanese 
EW net in the Indies practically intact. On very 
long-range raids like those to Balikpapan and 
Surabaya no feinting was possible, and the Jap- 
anese could have obtained early enough warn- 
ing to shift fighters to the target area. Elimina- 
tion of the radars which covered the route was 
therefore desirable. Radar busting was, on the 
other hand, out of the question in Formosa, be- 
cause of the denseness of the radar net on this 
highly developed island. It was never practiced 
against GL and SLC radars because of the 
danger involved. 

The attacks were first made by fighters or at- 
tack bombers after the station had previously 
been located by an RCM plane. Later on, the 
B-24’s of the 868th Squadron and the Navy’s 
PB4Y-l’s combined the functions of search and 
attack. Finally, several B-25’s were fitted with 
receivers and DF antennas, and assigned ex- 
clusively to radar busting. The Japanese prac- 
tice of shutting down when being homed on 
made necessary an approach on the deck (at a 
very low level) to delay detection, at maximum 
speed. The B-25 was the plane best suited for 
the job; the A-26 would, no doubt, have been 
even better when it became available. 

RCM AGAINST GL AND SLC Radar 

In the subsection entitled “Surface Vessels” 
under Section 15.5.4 it has already been told 
how gun-laying radars put in their appearance 
on Luzon and Formosa and how countermeas- 
ures were immediately started. 

The jamming of the GL at Clark Field was 
cut short by occupation of the area, and the 
main jamming effort in the SWPA was thence- 
forth against Formosa. From the end of Janu- 
ary 1945 to the end of June, when it had been 
rather thoroughly bombed out, Formosa was 
the principal target of the 5th Air Force. The 
activities involving RCM were of two sorts: 
day bombing by tight group formations of 18 


RCM IN THE U. S. AIR FORCES 


351 


to 24 planes (on big occasions several groups 
might bomb together), and night bombing by 
single radar-equipped planes. 

In the day operations, altitudes ranged from 
10,000 to 15,000 ft. Visual bomb runs, initially 
several minutes long, were soon shortened to 
less than a minute. Fighter escort was provided, 
in case the Japanese should decide to use their 


ous Marks, Models, and Modifications that 
might have been used) and the 78-mc band 
(Mark TA Model 3). They tracked Allied air- 
craft under all weather conditions, but whether 
they were used to control fire when optical con- 
trol was possible was never decided. There is no 
doubt of their use for fire control under blind 
conditions ; the mission of February 18, 1945, to 



Figure 10. Captured Japanese gun-laying and searchlight-control radar of the Mark IV type. Note the 
similarity between this equipment and the U.S. SCR-268 from which it was copied. 


large fighter strength in Formosa. The fighters 
never did come up, except against stragglers, 
and the escort could well have busied itself 
dropping Rope, had automatic dispensers for 
P-38's been available. The Formosa weather — 
undercast was the rule — made the use of H2X 
necessary and about one-half of the missions 
were effectively blind. The H2X bomb runs 
lasted several minutes. 

The GL radars operated in the 200-mc band 
(it never was possible to disentangle the vari- 


Takao, when the lead ship was hit immediately 
after the formation emerged from over 10/10 
undercast was a case in point. The formation 
had been tracked on its constant course for sev- 
eral minutes by both a 79-mc and a 201-mc 
radar, and the shells must have been fired be- 
fore it came into the open. No jammers were 
carried on this mission. 

The strongest targets had one radar in each 
band; the lesser ones had just one radar. The 
number of guns per target ranged from 25 to 



352 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


75; and the total damage rate (almost all the 
missions had some RCM protection) was about 
20 per cent. This rate refers to the percentage 
of planes holed out of all those shot at. 

The one-wave tactics prevented reliance on 
Window to the extent customary in Europe, 
where the Chaff laid by the first two or three 
hundred planes infested the target area to the 
great benefit of the subsequent hundreds. In the 
Pacific, where the one or two radars were ap- 
proached practically head on. Window would, 
in the long run, have had little self-screening 
value. It was, therefore, used as a supplement to 
electronic jamming, the main reliance being put 
on the latter. 

The Dina and the ARQ-8 were used against 
the 200-mc and 78-mc sets respectively; 25 of 
the former were on hand in January 1945, and 
25 of the latter, ordered on emergency requisi- 
tion in January, arrived early in March. The 
small number of radars per target made this 
small number of jammers, distributed on the 
basis of four of each per group, adequate. A 
kind of spot jamming was used. An APR-1 (or 
later APR-4) was installed in each jamming 
plane, and it and the jammers (preset to the 
expected frequencies) were attended by an 
RCM operator. Search was carried out en route. 
On the approach to the target, it was con- 
centrated on high prf signals in the known GL 
bands. As soon as one was heard tracking, the 
jammer was switched on and retuned from its 
preset value if necessary. The operator moni- 
tored both radar and jammer until the group 
was out of the target area, when the jammer 
was turned off. 

The night missions to Formosa were carried 
out by H2X ships detached from the 90th Bomb 
Group and by SCR-717B-equipped LAB planes 
of the 63rd Squadron (43rd Group). Difficulty 
was experienced from 200-mc SLC, and start- 
ing on January 22, 1945, these planes began to 
use Rope. The original tactic was for the planes 
to dispense a single roll and take evasive action 
whenever caught in a light. Later on, the quan- 
tities of Rope used were increased. 

The zone of operations of the Thirteenth Air 
Force at this time lay to the south of Manila, 
and GL jamming was not yet needed. The only 
SLC jamming carried out by the Thirteenth Air 


Force, other than the October 1944 Chaff effort 
over Balikpapan, was in connection with a 
series of strikes by the 868th Squadron against 
Surabaya. The raids, each one carried out dif- 
ferently, culminated in the show of May 7-8, 
1945. Four planes, including the Armed Ferret 
functioning as a special jammer, went in at be- 
tween 10,000 and 12,000 ft to bomb harbor in- 
stallations and drop Rope for the protection of 
the six planes which, about 10 min later, came 
in low at between 300 and 1,000 ft to attack 
ships. The former, as hoped, attracted the 
searchlights, permitting the low planes to make 
undisturbed runs. All of the high planes but 
the Armed Ferret had difficulty eluding the 
lights ; the Ferret had only to turn on its Dinas, 
tuned to the 200-mc signal being heard, to be 
able to evade easily the lights that were holding 
it. It circled the target, attracting searchlights 
by turning on its landing lights and evading 
them again by turning on its jammers, until all 
the other planes had made their getaway, and 
then it returned safely to base. 

Early in the summer of 1945, the Pacific com- 
mands were reorganized, and the Seventh Air 
Force (three B-24 Groups) was joined with the 
Fifth and Thirteenth under FEAF. The B-24 
strength of FEAF, based on Okinawa, was to 
be considerably expanded, and, in addition, a 
B-32 group, the 312th, was functioning under 
it. FEAF was to concentrate its strategic bomb- 
ing on Kyushu, with attention also being given 
to the China coast. Large quantities of RCM 
equipment were beginning to arrive, and the 
goal of 16 Group A jamming and search instal- 
lations per group, four of them to include DF 
antennas, was being reached. 

Miscellaneous RCM Activities 

In the mining of Manila Harbor, December 
14-15, 1944, RCM was directed against both 
EW and SLC radars. Twenty-four RAAF 
PBY’s, in two flights of twelve, mined Manila 
Harbor from 400 ft, with no loss or damage due 
to enemy action, despite the fact that the mis- 
sion had been generally regarded as suicidal. 
The protection was provided by the PBY Fer- 
ret, flying at 10,000 ft and using three jamming 
transmitters (two APT-l's, one APT-3) and a 
large quantity of Rope (CHR-2), and by an 


RCM IN THE U. S. AIR FORCES 


353 


RAAF PBY, flying at 4,000 to 5,000 ft and also 
sowing Rope. A total of 16 signals in the 100-, 
150-, and 200-mc bands were jammed, and in- 
termittent look-throughs showed that six of the 
stations were shut down for more than 30 min. 
The intercepts also showed that the radars still 
on the air were sweeping the Rope areas and 
the jamming plane in a confused manner. Anti- 
aircraft fire and searchlights were wild. 

The Japanese used Window, decoys, and very 
little electronic jamming (or probably none) 
against our radars at various times, the great- 
est use being made of Window cut for 200 me. 
Our countermeasure was an AJ training pro- 
gram, conducted principally by a field unit of 
Section 22. This troupe, which first used a Hud- 
son and later a C-47 airplane, went from base 
to base as the need arose. It used Dinas 
(APT-Es), Mandrels (APT-3’s), Rugs (APQ- 
2’s), and sine wave-modulated jammers, to- 
gether with Chaff and Rope. Lectures and mo- 
tion pictures on the ground went with the 
demonstrations. The training proved to be of 
great value in reducing the radar personnel’s 
learning time in combat. 

Effectiveness of the RCM 

The flak damage rate of the B-24’s over For- 
mosa — where the enemy used GL radar and we 
used RCM and where a large fraction of the 
missions were blind — was about the same as 
that experienced earlier in visual missions over 
Rabaul and Truk, where there was never any 
evidence of Japanese GL. Whether the Formosa 
damage rate would have been higher without 
RCM will never be known. But there is definite 
evidence that our jamming seriously interfered 
with the operation of the Japanese radars and 
that it therefore tended to undermine Japanese 
confidence in this new weapon. In at least three 
cases, Japanese radars went off the air when 
our jamming transmitters were turned on. In 
other cases, the radars being jammed proceeded 
to sweep, indicating our success in preventing 
tracking. Further evidence of the technical ef- 
fectiveness of the RCM is found in the introduc- 
tion of AJ measures by the Japanese. They gave 
up their practice of starting tracking with the 
Mark TA Model 3 at extreme range — which had 
given us ample time to retune the ARQ-8’s if 


necessary — and only turned these sets on at the 
beginning of the bombing run. There was also 
some indication of frequency shifts by the 200- 
mc radars, in order to evade the electronic jam- 
ming. 

No further conclusions on the effectiveness of 
the GL jamming can be drawn until post-hostili- 
ties intelligence from Japan is received. 

The Surabaya and Manila operations illus- 
trate the tactical benefit that can be derived 
from imaginative use of RCM against EW and 
SLC in night operations. The use made of heck- 
ling planes shows how RCM against EW can be 
of value even under visual conditions. 

Radar busting not only restricted the overall 
performance of the enemy EW net but also had 
immediate tactical value in some operations, 
such as the raids on Surabaya. Experience 
showed that radar busting alone could not be 
counted upon to destroy all EW radars in any 
particular area; the combination of physical 
attack with jamming and deception was far 
more effective than either by itself. 

The detection of the Japanese task force in 
the Camotes Sea by the PBY Ferret illustrates 
the immediate tactical value of radar recon- 
naissance. 


15.6.5 Operational Use of RCM in the 
India-Burma and China Theaters 

Organization 

In the India-Burma and China Theaters there 
were three American air forces. The Four- 
teenth Air Force in China and the 10th Air 
Force in Burma were essentially tactical air 
forces although they were using some heavy 
bombers. The Twentieth Bomber Command, 
which used B-29’s, was originally a completely 
independent organization, but in the latter part 
of 1944 it maintained close liaison with Head- 
quarters Army Air Forces India-Burma Thea- 
ter [AAF-IBT]. Since the theater was under 
the supreme command of a British officer, the 
organization of the American and the British 
RCM units had to be very close. For this pur- 
pose, in order to maintain liaison and coordina- 
tion with the other Allied organizations active 
in RCM, a committee was established consist- 


354 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


ing of representatives of AAF-IBT, RAF Air 
Command South Asia, Royal Navy East Indies 
Fleet, the Supreme Allied Command of South- 
east Asia, and the British Noise Investigation 
Bureau. Representatives of each of these or- 
ganizations met monthly at Kandy, Ceylon, for 
the purpose of establishing theater policies in 
regard to the use of offensive countermeasures 
and for exchanging current intelligence infor- 
mation. 

Search and Intelligence 

Throughout all the India-Burma and China 
Theaters, the RCM program was exclusively 
one of search and intelligence. RCM was an in- 
surance against possible effective use by the 
enemy of its radar weapons. When it became 
apparent that the enemy’s radar was of little 
value to him, all countermeasures equipment 
except search gear was put in storage for pos- 
sible future use. 

In June 1944, when the 20th Bomber Com- 
mand began its operations in Southeast Asia 
and China, and over the Japanese home island 
of Kyushu, there was only a limited amount of 
information available on Japanese radar. Virtu- 
ally nothing was known of enemy activities in 
China, whereas a small amount of information 
had been obtained on the home islands of Japan 
through coastal searches by Navy submarines. 
The British Navy and Royal Air Force had con- 
ducted fairly extensive RCM reconnaissance in 
Southeast Asia, but they were handicapped by 
a lack of adequate DF and measuring equip- 
ment. Although it was an established fact that 
the Japanese possessed a fairly extensive net- 
work of EW radars and ground observation 
posts, their locations were unknown; in addi- 
tion, little was known of their use of GL or SLC 
radars. It became apparent early in 1944, with 
the Allies assuming the offensive in these thea- 
ters, and with increased U. S. Air Forces activi- 
ties, that an extensive RCM reconnaissance 
program would be essential. 

An analysis of the early-warning and air- 
defense system in China and Kyushu was im- 
portant to the Twentieth Bomber Command and 
Fourteenth Air Force in the planning of future 
missions against possible strong enemy de- 
fenses. Likewise, such a requirement existed 


for the Twentieth Bomber Command and the 
Tenth Air Force in Burma and Southeast Asia, 
where such important targets as Rangoon and 
Singapore were encountered. 

The U. S. radar countermeasures program of 
reconnaissance and analysis in these theaters 
commenced in June 1944 with the initial strike 
missions of the India-based B-29’s of the Twen- 
tieth Bomber Command. For a period of ap- 
proximately 10 months these aircraft operated 
in Southeast Asia and China and over the Jap- 
anese home islands of Kyushu, providing a 
great deal of valuable information on enemy 
radar. Several months after the Twentieth 
Bomber Command’s search program was in- 
augurated, an interim B-24 Ferret, which was 
equipped in the theater, was provided to the 
Fourteenth Air Force for use in China. Ini- 
tially, this plane was to be used until Ferrets 
XII and XIII arrived from the United States; 
however, in November, when the Ferrets did 
arrive, it was found desirable to operate both 
the interim Ferret and Ferret XIII in China, 
leaving Ferret XII available for use in Burma. 

The three Ferrets and upwards of a dozen 
B-29’s were equipped with DF antennas and 
equipment which enabled the location and type 
of most enemy radars in the theater to be estab- 
lished. 

Twentieth Bomber Command. When the 
Twentieth Bomber Command commenced op- 
erations against targets on the Japanese home- 
land and in Southeast Asia, two significant con- 
ditions were met. First, fighter protection could 
not be afforded the long-range bombers on these 
missions ; and second, operations were con- 
ducted against areas which were not accessible 
to Ferret reconnaissance. In addition, general 
knowledge and specific data on the characteris- 
tics and operational use of enemy radar were 
very meager. As a consequence, this organiza- 
tion went overseas well equipped with RCM 
personnel and equipment. 

After the initial search work was accom- 
plished, and it was determined that the enemy 
did not offer a serious threat as far as GL and 
SLC radar was concerned, the jammers were 
bench tested and placed in weatherproof stor- 
age. Likewise, the supply of Rope and Chaff 
which had been received by water shipment was 


RCM IN THE U. S. AIR FORCES 


355 


placed in storage for possible future use either 
by the Twentieth Bomber Command or other 
Air Force organizations in the theater. 

The reconnaissance program was initiated by 
the search aircraft which had been equipped in 
the United States. Gradual modifications of this 
installation took place as new equipment was 
received and improvements were evolved. 

A requirement for the use of DF antennas 
was foreseen for the purpose of associating 
given radars with general areas in case jam- 
ming later became necessary. Three APA-24’s 
were top-mounted in search aircraft. These 
were found to be generally unsuitable, both be- 
cause of DF inaccuracies and because of trou- 
bles in the hydraulic drive. A bottom-mounted, 
retractable modification including electric drive 
was designed and built in the theater. These 
proved quite successful in operational use, and 
about two dozen were eventually installed. RRL 
later built an electric-drive unit which had to be 
modified in the field for use in the B-29’s. 

When it became apparent that the Japanese 
radar activity was confined to frequencies of 
200 me and lower, plans for the installation of 
the higher-frequency APA-17 automatic DF an- 
tennas were held up. The APR-7 search receiver 
was used for the monitoring of the 100- to 
3,000-mc range, while the APR-5A was kept on 
hand to cover this band in case enemy activity 
there required a receiver with higher selec- 
tivity. 

In addition to the program of radar recon- 
naissance by the Twentieth Bomber Command, 
a program for the investigation of Japanese 
fighter-control communications was initiated in 
February 1945. Nisei operators (Americans of 
Japanese ancestry) were flown as combat crew 
members to monitor enemy fighter and fighter- 
control frequencies to aid in the analysis of the 
Japanese use of communications. These com- 
munications nets were in general found to be 
highly inadequate. Prior to the departure of the 
Twentieth Bomber Command from India, a 
rather complete analysis of the early-warning 
net of Sumatra and the Malay Peninsula was 
carried out. 

An evaluation of the overall RCM effort of 
the Twentieth Bomber Command would indi- 
cate that the program of reconnaissance was 


essentially one of insurance. B-29’s gave the 
Allies the first real picture of the radar situa- 
tion on Japanese home islands and exploded the 
theory advanced by some that we could expect 
much better radar there than in the SWPA. 
While a few enemy GL and SLC radars were 
encountered, their effectiveness was never con- 
sidered great enough to warrant the use of of- 
fensive countermeasures by this organization. 
The lack of Japanese fighter strength and the 
long distances over which missions were flown 
eliminated the need for evasive action against 
the Japanese EW net. 

Activities of the Fourteenth Air Force. The 
need for separate Ferret aircraft in China to 
augment the search program of the Twentieth 
Bomber Command was realized in May 1944. 
This need was based on the fact that the activi- 
ties of the heavy bomb groups of the Fourteenth 
Air Force would be confined to different areas 
than those of the B-29’s and would, therefore, 
require additional reconnaissance. 

At this time, there were no Ferrets scheduled 
for arrival for at least 3 months, so arrange- 
ments were made for the construction of an in- 
terim Ferret in the theater. A B-24D was fur- 
nished by Southeast Asia Command, and the 
RCM equipment was furnished by the Twen- 
tieth Bomber Command. The Ferret was con- 
structed under the technical direction of an 
RRL technical observer and turned over to the 
Fourteenth Air Force early in September. Sev- 
eral months later Ferret XIII arrived from the 
United States. 

The Fourteenth Air Force adopted a plan 
providing a skeleton RCM organization which 
would have formed the nucleus of a large or- 
ganization had it become necessary to increase 
RCM activity. Additional personnel were 
brought into China so that increased personnel 
requirements could have been satisfied if the 
need arose. Small quantities of equipment were 
procured so that the personnel could become 
familiar with its operation. A supply of Rope 
was held in India so that it could be quickly 
flown over the '‘Hump” to China if its use be- 
came necessary. 

The two Ferrets carried out a modest pro- 
gram of reconnaissance operating sporadically 
for a period of about 4 or 5 months, with the 


356 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


gasoline shortage constantly hampering their 
activities. By the time that a fairly thorough 
reconnaissance program was completed in 
China, it was realized that because of the in- 
effectiveness of enemy radar there would be 
little value to continued operations. In May 
1945, the interim Ferret was converted to a 
gasoline tanker and Ferret XIII was trans- 
ferred to the FEAF in the Philippines, thereby 
closing the book on Fourteenth Air Force RCM 
activities in China. 

Activities of the Tenth Air Force. Ferret XII 
arrived in the theater in November 1944 and 
was attached to the only heavy bomb group of 
the Tenth Air Force. The Tenth Air Force op- 
erated under the jurisdiction of the Headquar- 
ters AAF-IBT and confined its operations to 
strategic bombing and to the aiding of Allied 



Figure 11. Runway and hardstands of North 
Field, Guam. This field was used by the 314th 
and 315th Wings of the Twenty-First Bomber 
Command. 

ground forces in Burma until May 1945. Prior 
to the arrival of this Ferret, RCM reconnais- 
sance had been performed in Burma both by 
strike aircraft of the 20th Bomber Command 
and by two RAF Ferrets of Air Command 
Southeast Asia. 

Ferret XII operated in Burma and the Anda- 
man Island chain from November 1944 until 
April 1945, permitting an accurate accounting 
of all enemy radar activity during this period. 
A Chain of EW radar stations was encountered 
along the Burma coast but it was soon discov- 
ered that they were not put to intelligent use. 


On many occasions Allied night-strike forma- 
tions succeeded in making their bomb runs on 
targets which were not even partially blacked 
out. Gun-laying radar was encountered for a 
period of about 3 weeks in Rangoon just prior 
to its capture. 

With the opening of the Ledo Road and the 
fall of Rangoon, American commitments in 
Burma were fulfilled. In May 1945, American 
Air Force activity in Burma ceased, and Ferret 
XII was then transferred to the FEAF in the 
Philippines. The RRL technical observer assist- 
ing this aircraft proceeded to the Twentieth Air 
Force on Guam. 


15.6.6 Operational Use of RCM in the 
Central and Western Pacific 

Organization 

The top theater Air Force organization in 
the Central and Western Pacific was Head- 
quarters Army Air Forces, Pacific Ocean Areas 
[AAFPOA], which had under its direct con- 
trol units of the Seventh Air Force. The 
AAFPOA organization also acted as Deputy 
Commander Twentieth Air Force in the Pacific 
Ocean Area, and as such, DepComAF 20 had 
control over the Twenty-first Bomber Command 
of the 20th Air Force. AAFPOA and DepCom- 
AF 20 were dissolved in the late spring of 1945, 
and the organization became United States 
Army Strategic Air Forces [USASTAF], with 
command power over the Eighth and Twentieth 
Air Forces in the Pacific. 

The RCM organizations within AAFPOA 
were under the Director of Intelligence and the 
Director of Communications. Under the Direc- 
tor of Communications was the Countermeas- 
ures Air Analysis Center [CAAC], which was 
planned as the organization in the theater 
charged with the job of assembling and analyz- 
ing the results of all RCM reconnaissance work 
done by Army Air Force units. During most of 
its existence, CAAC maintained close liaison 
with the RCM analysis organization at 
CINCPAC (Navy) Headquarters. CAAC un- 
dertook analyses of the Japanese air defense 
system from information derived from airborne 
and ground-based communication intercepts. 


RCM IN THE U. S. AIR FORCES 


357 


The Director of Communications and CAAC 
also had control over the Eighth Radio- Squad- 
ron Mobile, a ground-based communication in- 
tercept unit, and Beavers IV and V, ground- 
based intercept and jamming units. Informa- 
tion derived from these two sources was also 
used by CAAC in their analysis work. The RCM 
work done under the Director of Intelligence 
involved, for the most part, the compilation and 
publication of radar coverage maps of Japa- 
nese-held territories in the Central and Western 
Pacific Areas. 

The RCM organization within the Twenty- 
first Bomber Command was essentially an oper- 
ational one, attached to the Communications 
Section of the Headquarters. No RCM analysis 
organization existed under the A-2 Section of 
the bomber command, and, although much of 
this work was done by personnel in the Com- 
munications Section, it was planned to depend 
upon CAAC for the technical analysis and in- 
telligence functions normally found in Bomber 
Command A-2. 

The five Ferret aircraft assigned to the thea- 
ter were attached to the Third Photo-Recon- 
naissance Squadron, a subordinate unit of the 
Twenty-first Bomber Command. The Ferrets 
were under Third Photo for administration and 
maintenance but were under the operational 
control of the RCM officer of the Twenty-first 
Bomber Command. In practice, however, the 
plans for weekly Ferret flights were made at 
CAAC and passed on to the Ferret flight 
through the Twenty-first Bomber Command 
RCM officer. Data gathered by the Ferrets were 
sent through the Twenty-first Bomber Com- 
mand to CAAC for analysis and distribution. 

Search and Intelligence 

By far the most extensive RCM reconnais- 
sance program carried on in this theater was 
that undertaken by units of the Twenty-first 
Bomber Command. The bomber command 
(later Twentieth Air Force) consisted of five 
wings, and, at first, targets were usually hit by 
single wings. Consequently, the need was felt 
for an RCM reconnaissance program which 
would be complete within each wing. When op- 
erations began, neither B-24 nor B-29 Ferret 
aircraft were available in the theater, and it 


was necessary to conduct reconnaissance from 
the strike aircraft themselves. While other air- 
craft could have done a satisfactory job of plot- 
ting EW radars, it was necessary to have the 
intercept operator fly within the bomber forma- 
tion in order to obtain the necessary informa- 
tion on GL and SLC radar. 

No group was willing to give up too many of 
its aircraft for RCM search purposes, and since 
the RCM observers and equipment were also 
divided equally between the groups in a wing, 
the reconnaissance job was divided between the 
four groups in each wing. Each group was ex- 
pected to provide one observer and RCM- 
equipped aircraft per mission, giving the possi- 
bility of four observers over the target, barring 
possible mishaps. 

The standard RCM reconnaissance equip- 
ment was available in various quantities. Some 
APA-24’s were received through Navy Supply 
Channels, but APA-17 arrived too late to be in- 
stalled before World War II ended. In order to 
ensure that one RCM-equipped B-29 per group 
would be available, two aircraft per bomb 
squadron, or a total of six aircraft per bomb 
group, were equipped with Group A parts, in- 
cluding antennas, for all the reconnaissance 
equipment available. This, in itself, was not a 
difficult job because racks, power cables, in- 
verters, and r-f cables to the antenna positions 
were installed in all aircraft in the United 
States. 

Plans were made for the use of the APA-24 
DF antenna on the strike B-29's. This was of 
necessity a compromise because strike aircraft 
must fly a prescribed course, often not the most 
desirable from a DF point of view, and naviga- 
tion in the strike aircraft is seldom as precise 
as is desirable in Ferreting work. On the other 
hand, it was necessary to be in the target area 
when a strike was under way in order to hear 
any DF gun-laying and searchlight-control 
radar signals. Although the inherent inaccura- 
cies in DF work using the APA-24 were well 
known, it was felt that DF on GL signals would 
give an indication of the area distribution of 
GL radars in a given target area or in adjacent 
target areas. Whether this could be done with 
significant results was never determined. Many 
cuts on EW radars in the Nanpo Shoto island 


358 


RCIVI IN THE PACIFIC THEATERS OF OPERATIONS 


chain and on the southern coast of Japan itself 
were obtained, and also it was definitely proved 
that a 70-mc radar, having characteristics simi- 
lar to the Mark CHI, was being used on ships, 
probably picket boats. 

Actual DF operations by the B-29’s were not 
great. The few APA-24’s that were finally built 
in the theater and the APA-24’s received from 
the Navy did not get into useful operation be- 
fore the end of World War II. The 58th Bomb 
Wing arrived on Tinian from India with 12 bot- 
tom-mount, electric-drive APA-24's and did the 
only satisfactory DF work from the B-29’s. 
With the experienced operators available, the 
58th Wing turned in some very good locations 
of EW radars and radar-equipped picket boats. 
Some little work was done in approximately lo- 
cating radars by manual left-right switching of 
symmetrical antennas on the plane, with moder- 
ate success. The APA-17 with the 1,000- to 
5,000-mc antenna would have been especially 
valuable in determining whether the 10-cm 
signals heard were land-based or ship-based, 
and it is indeed unfortunate that the first unit 
of this equipment did not reach the theater until 
two weeks before the end of World War II. 

A limited program of airborne communica- 
tions intercept work was carried on in the 
Twenty-first Bomber Command. ARR-5 com- 
munication receivers and disk recorders (later 
replaced, in part, by wire recorders) were avail- 
able in quantity. Lack of ARR-7 until the sum- 
mer of 1945 necessitated the use of the BC-348 
communication receiver for frequencies be- 
tween 5 and 15 me. The quality of the record- 
ings made was never good; this was due both 
to lack of experience on the part of the opera- 
tors and to equipment limitations, and the pro- 
gram yielded little in the way of usable results. 

RCM observers accompanied several single- 
plane weather strike missions a week and con- 
firmed the fact that there was little EW radar 
activity and practically no GL/SLC activity on 
the part of the Japanese when a single plane 
appeared. RCM reconnaissance was also carried 
on a number of radar-scope photo missions. All 
mining missions were accompanied by RCM 
observers and good success was had in obtain- 
ing information on Japanese SLC radar, on 
which future offensive action was based. RCM 


observers often accompanied Superdumbos 
(B-29’s used for air-sea rescue work) and navi- 
gational B-29’s used to lead fighters to Japan, 
and were able to spend an hour or more in the 
target area while the strike was going on. 

The data collected from all the previously 
mentioned searches were consolidated at wing 
level and forwarded to Headquarters, 21st 
Bomber Command. Because the Countermeas- 
ures Air Analysis Center never did have suffi- 
cient personnel to handle the job, it was neces- 
sary to consolidate the wing reports at bomber 
command level, analyze the results, and distrib- 
ute the information to both higher and lower 
echelons. As CAAC gained personnel, that or- 
ganization was to take over the analysis and 
RCM information distribution for the 21st 
Bomber Command. 

The primary job given to the Ferrets was 
that of mapping the radars in the Nanpo Shoto 
chain of islands from I wo Jima to Tokyo Bay. 
Submarine intercepts and airborne intercepts 
indicated an extensive EW chain through the 
Nanpo Shotos and actual locations needed veri- 
fication. B-29 strikes were usually routed so 
that they followed the island chain on their trip 
north. Although this gave long early warning 
to the Japanese, it was felt that this price could 
be paid for the great simplification in the navi- 
gational problem of the B-29’s. However, if the 
radars could be located by DF, photographed, 
and then eliminated by bombing and strafing, 
the navigational advantages of the islands could 
be used without the disadvantage of added early 
warning for the Japanese. The pinpointing of 
the EW radars was the first step in this plan, to 
be followed by photographs and then radar 
busting. 

The Ferrets, operating from Guam, got their 
operational training working around Haha 
Jima and Chichi Jima. Then, staging through 
Iwo Jima, they worked their way north along 
the island chain, returning to each island until 
all radars were accurately pinpointed. Before 
World War II ended, the Ferrets had succeeded 
in completely mapping the Nanpo Shoto chain 
from Haha Jima to Sagami Bay and the photo- 
graphing phase of the work had begun. The 
Ferrets also had mapped many of the radars on 
the southern coast of Honshu by V-J Day. 


RCM IN THE U. S. AIR FORCES 


359 


In addition to their duties as radar Ferrets, 
communications intercept work was carried on 
by the four B-24’s. The oldest plane, Ferret VI, 
was stripped of all armament, except flexible 
tail guns, for night missions, and two radio in- 
tercept positions were installed in the nose. The 
other Ferrets had one radio intercept position 
installed in the bomb bay RCM compartment. 
Nisei operators were used for the communica- 
tions work with good success. The Ferrets op- 
erated during the time that a B-29 strike was 
going on and stayed about 50 miles off the coast 
of Japan all during the strike. The communica- 
tions intercept program in the Ferrets was 
quite successful. 

Information gathered by the Ferrets was 
first consolidated within their own organization, 



Figure 12. RCM shack, 330th Group, 314th 
Wing, North Field, Guam. 


and a special officer, known as an RCM inter- 
preter, was provided for this purpose. The in- 
formation was then passed through the Twenty- 
first Bomber Command RCM officer to CAAC, 
where consolidation of this information with 
that arriving from other sources was made. The 
Countermeasures Air Analysis Center put out 
a weekly summary of Ferret activities and re- 
sults, and, on the basis of the previous week's 
results, wrote the directive setting up the Fer- 
ret flights for the following week. 

Seventh Air Force RCM reconnaissance ac- 
tivities were very limited in scope, both because 
of lack of personnel and lack of equipment. 
Three aircraft of the Thirtieth Bomb Group 


(H) were fitted with Group A parts for the 
APR-4 receiver and the APA-6 pulse analyzer. 
The only RCM officer in the Seventh Air Force 
was the one attached to Air Force Headquar- 
ters, and he flew in the RCM-equipped planes of 
the Thirtieth Bomb Group as intercept op- 
erator. The Seventh Air Force, at the time that 
it was deployed in the Marianas, was flying 
against I wo Jima, Haha and Chichi Jima, Truk, 
and Marcus Island. Most of the EW radars on 
these islands were logged and the information 
was forwarded to the organization which pre- 
ceded CAAC. 

Early-Warning Countermeasures 

Aside from the very limited radar-busting 
activities mentioned in the previous section, the 
only active countermeasures against EW radar 
employed in this theater were deceptions. When 
the 21st Bomber Command commenced opera- 
tions in the theater, the potential of the Japa- 
nese Air Defense system was almost unknown, 
as were enemy methods of vectoring fighters 
and enemy zones of air defense. It was believed 
that diversionary efforts might be successful in 
reducing fighter opposition at a target, if some 
of the fighters from the area could be drawn to 
another target by the diversionary force. The 
tactics employed were of the simplest kind. A 
small number of aircraft, usually two or three, 
were dispatched to the diversionary target and, 
when they were about 150 miles off the coast of 
Japan, commenced dropping sufficient quanti- 
ties of Rope to simulate a force of about 12 
B-29’s. The evaluation of the effectiveness of 
these diversionary efforts is extremely difficult ; 
the enemy reaction to the main force was 
always much greater than the effort against the 
diversionary force. It should be noted that all 
of the diversions were flown in daylight. Since 
the B-29 tactics were constantly changing and 
different targets were hit on each of these mis- 
sions, what fighter interception would have 
been encountered without the diversion is diffi- 
cut to assess. 

The tactical air force of the Tenth Army, 
based on Okinawa, conducted an RCM diversion 
over Kyushu in early June of 1945, in support 
of two photo-reconnaissance Liberators of the 
Navy VD-1, who were to photograph southern 


360 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


Kyushu. Enemy fighter strength was not com- 
pletely known, but any fighter opposition at all 
would make the successful accomplishment of 
the photo mission almost impossible. Eight 
P-47’s were sent in a diversionary raid to the 
Sasebo Naval Base in northwestern Kyushu. 
The diversionary aircraft dispersed Rope on 
the way to Sasebo to mask the number of air- 
craft actually present. No enemy fighter air- 
craft were sighted by the Liberators during the 
time that they were accomplishing their photo- 
graphic mission. The diversionary aircraft and 
some opportunist fighters encountered some 
enemy fighters near Sasebo and shot down sev- 
eral. As in the previously mentioned diversions, 
evaluation of the effectiveness of the RCM tac- 
tics used is nebulous at best and no definite con- 
clusion as to its success can be drawn. 

GL AND SLC Countermeasures 

Operational Problem, GL/SLC type signals 
had been intercepted in the Balikpapan area in 
late 1944 by Fifth Air Force units, but the first 
confirmed intercept of a 200-mc GL/SLC signal 
definitely associated with flak bursts made by 
Twenty-first Bomber Command units was on a 
mission to Tokyo on January 27, 1945. It is very 
likely that GL radars were being used against 
the B-29’s during the months of December and 
January also, but the intercept program did not 
begin to produce usable information until this 
mission to Tokyo. The first confirmed intercept 
of the Mark TA Model 3 occurred during the 
first week in February 1945 but was not asso- 
ciated with enemy flak. 

During the period February through May 
1945, there were numerous occasions where 
continuously pointed fire was observed through 
undercast. In many cases GL type radar signals 
were observed, locked on the formation being 
subjected to the continuously pointed fire. How- 
ever, blind fire, while obviously radar-con- 
trolled, was not consistent in its accuracy, and 
for the most part was inaccurate. Radar-con- 
trolled flak did improve in accuracy as opera- 
tions continued but never approached German 
flak in quantity and accuracy. 

The major problem encountered by the 
Twenty-first Bomber Command was that of 
radar-controlled searchlights. Because of diffi- 


culties encountered in daylight high-altitude 
precision bombing, the Twenty-first Bomber 
Command commenced low-altitude night mis- 
sions in early March 1945. The advent of these 
raids gave the first clear picture of the search- 
light defenses available to the Japanese and the 
tactics employed by them. It was found that at 
night the Japanese only fired on planes which 
were illuminated by searchlights; only very 
rarely were unilluminated planes fired upon. 
Fighter attacks were only made against those 
planes which were caught in the searchlight 
beams. The lack of fighter attacks against un- 
illuminated aircraft indicated lack of satisfac- 
tory fighter-vectoring methods and the absence 
of a usable AI radar in Japanese night fighter 
aircraft. Thus, radar-controlled searchlights 
constituted the only menace to night operations. 

The first night ''fire’’ raids in March 1945 
showed a crude searchlight defense. There were 
a number of master searchlights, obviously 
radar-controlled, which were used to direct 
optically controlled lights on the target. As 
many as 20 searchlights would carry one plane 
as it crossed the target area, giving many 
others a "free ride.” As the raids continued 
through March and April the searchlight tac- 
tics improved and, with the aid of the radar- 
controlled master lights, pairs of lights were 
used to pass individual aircraft along over the 
target area, giving the enemy a much better 
utilization of the searchlights available to him. 
By May 1945, the searchlight defenses of the 
enemy were operating very efficiently and posed 
a serious problem. 

Efforts were made to reduce the effectiveness 
of the searchlight defenses by saturation meth- 
ods with good success. The bomber stream was 
compressed as much as possible, so that all of 
the aircraft passed over the target area in the 
minimum length of time, with the minimum in- 
terval between individual aircraft. The effec- 
tiveness of these tactics was evidenced by the 
fact that the first aircraft over the target area 
encountered well-organized searchlight tactics, 
whereas, as the raid progressed and more air- 
craft came into the target area, the searchlights 
became disorganized and their previously well- 
coordinated actions ceased. This is reasonable 
from the radar point of view. With many air- 


RCM IN THE U. S. AIR FORCES 


361 


craft at altitudes of 5,000-10,000 ft on sev- 
eral axes of attack, all in the target area at 
once, the operation of the 1-f radars used by the 
Japanese would be seriously hampered by long, 
minimum-range, permanent echoes at short 
range and by the wide beamwidths inherent in 
these radars. 

Searchlights also showed themselves to be a 
problem in the night mining operations of the 
313th Wing. The majority of the mining mis- 
sions carried out by the 313th Wing were to the 
Inland Sea area, with particular emphasis on 
keeping the Shimonoseki Straits closed to ship- 
ping. The searchlight and flak defenses in this 
area were quite extensive and the individual 
mining aircraft operating at altitudes below 
5,000 ft were being caused considerable trouble 
by radar-controlled searchlights. 

Studies of reconnaissance information had 
indicated that the Japanese were employing 
radars in bands centered at 78 me and 200 me 
for gun-laying and searchlight-control pur- 
poses. The 78-mc radar was obviously the Mark 
TA Model 3, copied from the British GL Mark 
II. Photo-reconnaissance had shown a number 
of bowl-shaped depressions alongside heavy gun 
batteries and their diameter was that which 
was normally used with the Mark TA Model 3. 
However, it was never definitely determined 
whether or not the Mark TA Model 3 was being 
used for GL only, or for GL and SLC purposes. 
The picture was less clear at 200 me. Captured 
documents had mentioned a number of 200-mc 
radars which were designed for GL and SLC 
work, but their intercept characteristics were 
similar enough to make identification on that 
basis difficult. It was never definite which of the 
200-mc radars were being used for GL and 
which for SLC. 

Of the total number of intercepts of radars 
having GL/SLC characteristics approximately 
55 per cent were in the 200-mc band and 45 per 
cent were in the 78-mc band. The total fre- 
quency spread observed on the Mark TA Model 
3 radars was 72-85 me, with 92 per cent of the 
signals appearing between 74-80 me. At 200 
me the total frequency spread observed was 
180-220 me, with 88 per cent of the radars op- 
erating between 180-210 me. The median on 
pulse length for the 200-mc radar was 5 \isec, 


and for 78-mc radars was 7 psec. 

Bombing on daylight missions was done in a 
column of flight squadrons, each consisting of 9 
to 11 B-29’s. Flight squadrons were usually 
separated far enough in trail, so that for RCM 
planning purposes each squadron had to be in- 
dependently self-shielding against both 78-mc 
and 200-mc radars. At night, bomb runs were 
made individually, in a long column of single 
aircraft, on the same axis of attack, and at the 
same altitude. Each aircraft had to be protected 
individually from the previously mentioned 
radars and could not depend on other strike air- 
craft for mutual shielding. 

Electronic Jammers, The B-29 groups were 
fortunate compared to the groups in the Euro- 
pean and Mediterranean Theaters of Opera- 
tions, in that they arrived in the theater 
equipped with Group A installations for all of 
the standard RCM equipment. There was pro- 
vided a frame with shock mounts for two A-ID 
SAR units and four B-ID SAR units. A PE-218 
inverter was provided for RCM power, and 
power cables and connectors came already in- 
stalled. Antenna ports were provided on every 
plane, which were satisfactory for search work 
but not for jamming, and antenna cables were 
installed. Thus there were facilities provided 
within the B-29 which made the installation of 
barrage- jamming equipment a simple matter. 
A simple field modification of the RCM position 
gave a satisfactory spot- jamming position. Al- 
though all antenna ports provided gave either 
vertical polarization or cross polarization 
(when horizontal polarization was required for 
jamming) with stub antennas, they were a 
help in getting started. 

It appeared most economical at 200 me to 
employ barrage jamming in the band 190-210 
me, and to use spot jamming to cover the bands 
180-190 me and 210-220 me. Calculations indi- 
cated that 11 Dina transmitters spaced 2 me 
apart would protect 11 B-29’s to a minimum 
range of about 31/2 niiles against the 200-mc 
radar most difficult to jam. This required the 
equivalent of one Dina per aircraft in the flight 
squadron. High-powered amplifiers for the Dina 
were on order for use in the event that subse- 
quent tests in the United States showed that 
more jamming power was needed, and the few 


362 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


received were used on the Dinas set to the cen- 
ter of the frequency band. In some cases Rugs, 
which would tune down to 200 me, were used for 
barrage jamming also. For 180- to 190-mc and 
210- to 220-mc spot jamming, an operator was 
assigned to each of these bands and ordered to 
jam all GL/SLC signals appearing in his as- 
signed sector. Each spot-jamming operator was 
supplied with three transmitters, a “setting-on” 
receiver (APR-4), and a pulse analyzer (later 
to be replaced by a panoramic adapter) . Dinas, 
modified for spot jamming, were used in most 
cases but were being replaced by Rugs which 
had been modified for single-dial operation. The 
pulse analyzer was necessary to distinguish be- 
tween EW radars operating on the same fre- 
quency as the GL/SLC radars. There were to be 
Group A installations for spot jamming in six 
aircraft per bomb squadron, to ensure that each 
flight squadron would have two spot-jamming 
installations on everyday missions. This pro- 
gram was never completely carried out during 
World War II because of a shortage of APR-4 
receivers and spot-jamming operators. The 
RCM observers flew on spot- jamming opera- 
tions, but their numbers were insufficient to 
permit the use of two operators per flight 
squadron. Shortly before the end of the war, the 
spot- jamming operator training program began 
to produce a number of men, and the arrival 
of sufficient quantities of APR-4's permitted a 
partial realization of the goal of the spot-jam- 
ming program. 

Because of the smaller band to be jammed, it 
was decided to use barrage jamming exclusively 
in the frequency band 72-84 me and to reserve 
spot-jamming efforts until frequency spreading 
on the part of the enemy radar appeared. Cal- 
culations showed that seven ARQ-8’s, spaced 2 
me apart, would protect 11 B-29's to a minimum 
range of 1.5 miles against the Mark TA Model 
3 radar. This program of barrage jamming at 
78 me was never carried out as planned because 
of the lack of sufficient quantities of ARQ-8. 
The usual practice was to set the one or two 
ARQ-8’s available to each bomb squadron to 
the center of the band 72-84 me and forego pro- 
tection over the rest of the band. Often the spot- 
jamming operators would carry the lone ARQ-8 
along with their 200-mc jammers and move it 


around in the band to cover the greatest pos- 
sible number of signals. A small number of 
high-power amplifiers for the ARQ-8 were re- 
ceived, and many more were on order. These 
were used with the barrage jammers. 

The very nature of the formations flown at 
night made the job of electronic jamming in- 
finitely more difficult than that in daylight op- 
erations. Since individual aircraft could not de- 
pend upon other aircraft in the bomber stream 
for protection, no effective jamming could be 
done from the strike aircraft themselves with- 
out carrying an inordinately large number of 
transmitters in each plane. Consequently the 
idea of using special aircraft to provide jam- 
ming cover for the bomber stream arose. Be- 
cause each special jamming plane was to carry 
a large number of jamming transmitters with 
the corresponding requirement for many an- 
tennas on the skin of the ship, the planes be- 
came known as Porcupines. One wing, having 
a more idealistic approach to the problem, called 
their special jamming aircraft “Guardian An- 
gels.” 

The wide beamwidths and appreciable side 
and back lobes inherent in the Japanese 78-mc 
and 200-mc radars made them susceptible to 
off -target jamming to a certain extent. Since 
the requirement would be that of shielding only 
a single aircraft at a time by this off-target 
jamming, it was believed that such shielding 
could be accomplished with the use of reason- 
able jamming powers. The plan was to equip 
four aircraft per wing, each with sufficient 
equipment to jam completely both the 78-mc 
and 200-mc GL/SLC bands. These aircraft 
would precede the strike aircraft to the target 
area and would fly parallel to the bomber 
stream, at a slightly higher altitude (for air 
safety purposes), describing a flattened oval be- 
tween the target and a point outside the target 
area, with the long axis of the oval parallel to 
the axis of attack of the strike aircraft. With 
four Porcupines flying this course in a random 
fashion among themselves it was felt that there 
would be a good chance that at least one of them 
would be in the main lobe of the radar and the 
other three would be contributing their jam- 
ming through the side and back lobes of the 
radar. On strikes involving more than one wing. 


RCM IN THE U. S. AIR FORCES 


363 


each wing was expected to contribute four Por- 
cupines. 

In order for each Porcupine to jam both 78 
and 200 me it was estimated that each plane 
would have to carry at least eight 200-mc bar- 
rage jammers, five 78-mc barrage jammers, and 
two spot- jamming operators, one covering 210- 
220 me, the other covering 180-190 me. No im- 
mediate plans were made for using spot jam- 
ming in the 78-mc band, reliance being placed 
on barrage jamming. It seemed very likely that 
it would be necessary to carry amplifiers for the 
200-mc jammers, and possibly even for the 
78-mc jammers, in order to reduce the mini- 
mum jamming range to a safe value. 

There were numerous mechanical problems 
involved in making such an installation in the 
B-29, particularly those of space, power, and 
location of antennas. Two different types of in- 
stallations were being investigated when World 
War II ended, in an effort to determine the most 
practical way of installing all of the equipment 
in the B-29. Use of Rope by the Porcupine will 
be discussed in the next section of this report. 

A Porcupine meeting all of the requirements 
stated in the previous paragraph was never 
built before the end of hostilities. Every wing 
except the 315th Wing (the last wing to begin 
operation) had four ‘interim Porcupines'' 
carrying from 6 to 14 transmitters, and these 
were used on a number of night missions during 
June and July 1945. As soon as a satisfactory 
Porcupine, meeting all the operational require- 
ments, was devised, all of the interim Porcu- 
pines were to be converted according to this 
pattern. 

With the Porcupines available, the use of 
electronic jammers in strike aircraft on night 
missions was of questionable value. However, 
since equipment was often available, transmit- 
ters were installed in strike aircraft for what 
little protection they might chance to offer. 

Jammers were used extensively in mining 
operations. Mining aircraft were provided with 
several Dina transmitters and ARQ-8's, when 
available, set to the center of the band, and, 
where possible, spot- jamming operators were 
carried. Assuming that all of the radars ^fiook- 
ing at" these aircraft could be jammed by the 
relatively few transmitters carried, range 


might be destroyed and some benefit obtained 
even if the radars could DF on the jamming 
from the single aircraft. There was some fear 
that radar plots of the mining aircraft would 
aid the Japanese in sweeping the mines, and 
elimination of the range information available 
from the GL/SLC type radars would force the 
enemy to depend upon his less accurate EW 
radars for this data. In one instance when four 
aircraft were sent to mine Tokyo Harbor at 
5,000 ft, they were equipped with jammers, and, 
in addition, two Superdumbos (B-29's used for 
air-sea rescue work) orbited the target area 
carrying spot-jamming operators and dispens- 
ing Rope. Searchlights were observed, but not 
one ever locked on the mining aircraft. 

Rope. The physical characteristics of Rope 
were described in a previous section of this re- 
port and mention was made of its response 
being a function of frequency. A bundle of Rope 
(three rolls in a sleeve) gave a response at 
200 me which was 0.8 unit (where 1 unit is 
equal to the echo from a B-17 head on) and a 
response at 78 me which was 1.5 units. Pre- 
liminary measurements showed that a B-29 
had an echoing area of about 1.7 units, conse- 
quently, two bundles of Rope would just give 
sufficient amplitude shielding to a single B-29 
at 200 me. The average pulse lengths at 78 and 
200 me were 7 and 5 psec respectively, but pulse 
lengths as short as 2 pisec had been observed, 
mostly for the 200-mc radars. Thus, all calcula- 
tions of quantity and dropping rate were made 
on the basis of shielding at 200 me and there 
was more than enough Rope present for shield- 
ing at 78 me. A dropping rate of one bundle of 
Rope per second was found by calculation to be 
sufficient to shield a single B-29 at the air 
speeds employed. 

The flight squadron (9-11 B-29's) employed 
on day missions could all be contained in a 
single "‘pulse packet" and the infestation of 
space with Rope had to be sufficient to shield 
completely this number of aircraft. The rela- 
tively slow rate of fall of Rope ideally would 
have allowed dispensing from every third flight 
squadron in the column of squadrons with full 
protection being afforded, but in practice this 
was impossible. Assembly and navigation dif- 
ficulties made it almost impossible to depend 


364 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


upon any one squadron’s being at the point in 
the bomber stream that was planned for it, and 
so it was necessary for each squadron to dis- 
pense Rope. Each B-29 was to be supplied with 
enough Rope to dispense at a rate of one bundle 
per second from the initial point [IP] (or a 
point closer to the target area if the IP was very 
far out of GL/SLC radar range) to a point just 
past the target area. No fighters were available 
which could carry automatic dispensers and 
still make the trip to Japan and back, so that 
the lead squadron had to depend upon electronic 
jamming for protection. 

The wide spacing between individual aircraft 
in the bomber stream on night missions pre- 
vented aircraft from depending upon the Rope 
dispensed by preceding planes for protection. 
However, a full complement of Rope was to be 
carried at night, anyway, because it was felt 
that an eventual infestation of the target area 
and approaches would result after the first hun- 
dred or so planes had gone over the target, and 
the confusion value would be great. To improve 
the infestation at night it was planned to pro- 
vide the Porcupines with sufficient quantities of 
Rope to dispense all the time that they were on 
the upwind leg of their oval course. This Rope 
would then drift into the path of the bomber 
stream. About 2,000 bundles of Rope were to be 
carried by each Porcupine, with provisions for 
automatic dispensing. 

The plans for day and night use of Rope as 
outlined were never completely carried out. The 
reasons for this were twofold : first, quantities 
of Rope sufficient to allow continuous dispensing 
in the target area were never available; and, 
second, it was physically difficult to dispense 
Rope from the B-29. Rope supplies in the 
Twenty-first Bomber Command never met the 
demand, and it was not until the first of July 
1945 that quantities of Rope approaching 200,- 
000 bundles a month reached the theater. The 
requirement stated for the Twenty-first Bomber 
Command was 1.5 million bundles of RR- 
3/U(T) per month. Because of the scarcity of 
Rope it was necessary to use the small supplies 
available in elementary deceptive tactics to 
“lose” flak and searchlights. B-29 crews were 
instructed to dispense three bundles of Rope 
every 10 sec any time that searchlights ap- 


peared to be swinging toward them or flak ap- 
peared to be “walking” dangerously close. This 
quantity of Rope dispensed at the rate men- 
tioned would give discreet “pips” on the scope 
of the Japanese GL/SLC radar. These simple 
deceptive tactics should not have fooled any 
radar operator more than one or two times, and 
yet this method of using the meager supplies of 
Rope available was successful in many cases for 
over three months in helping B-29’s to elude 
enemy radar-controlled flak and searchlights. 
It was obvious that once a plane had been 
“coned” by a searchlight, no amount of Rope 
dropping would be effective in helping the plane 
to elude the searchlight because it was probable 
that the enemy went over to optical control as 
soon as an aircraft was coned. This, of course, 
was borne out by actual experiences. In other 
cases aircraft which started dispensing Rope 
when searchlights were seen pointing in op- 
posite directions from the plane, found them- 
selves almost immediately coned. This story was 
used as an object lesson to crews in an effort 
to show them the danger of not using their 
meager Rope supply according to instructions. 
As Rope supplies increased, these elementary 
deception tactics gave way to continuous dis- 
pensing so that the Rope program was gradually 
changing toward the continuous dispensing tac- 
tics outlined in the previous paragraph. 

Dispensing Rope from the B-29 by hand was 
a difficult task under high-altitude conditions of 
operation. The pressurized construction of the 
B-29 made dispensing practically impossible 
from within the pressurized portions. The most 
convenient place for dispensing Rope in the 
B-29 was through the camera hatch in the rear 
unpressurized section. This method of dispens- 
ing was used in the early deception raids at high 
altitude and was very unsatisfactory. On more 
than one occasion the crew member dispensing 
Rope nearly lost his life because of mechanical 
difficulties with his oxygen hose. At the lower 
altitudes used in most of the night fire raids, 
pressurization and oxygen were not a serious 
problem and dispensing through the camera 
hatch could be tolerated. Again, however, there 
was also need for the camera hatch for the pur- 
pose for which it was designed, and when 
cameras for strike photos were carried, dis- 


RCM IN THE U. S. AIR FORCES 


365 


pensing between the camera and the edge of the 
camera hatch was a difficult task. Thus, the 
need for automatic dispensing equipment in the 
B-29 was very apparent. 

Work on an automatic Rope-dispensing in- 
stallation was started during February 1945. 
Through the spring of 1945, several different 
type installations were attempted with varying 
degrees of success. It was finally decided that 
each aircraft should have a maximum capacity 
of 720 bundles of Rope, and that installation in 
the rear unpressurized tail section of the B-29 
was the best solution. This installation was com- 
pleted and flight-tested by the end of June 1945, 
and the Air Depot, Guam, went into production 
on installation kits. At that time, 400 A-1 dis- 
pensers were on hand in the air depot and an- 
other 600 were on their way to the theater by 
air. Prototype installations had been made in 
one aircraft of each group by the end of July 
1945 and the complete installation program 
should have been well on its way to completion 
by September 15, 1945. The delay in arriving at 
a satisfactory installation of the automatic dis- 
penser, with the subsequent delay of the in- 
stallation program, did not seriously hinder 
Rope operations in the Twenty-first Bomber 
Command because adequate supplies of taped 
Rope, for use with the A-1 stripper, had not yet 
arrived in the theater by August 1, 1945. 

Rope was used quite consistently on all mining 
missions. For the most part the elementary de- 
ception tactics mentioned in the previous para- 
graph were used simply because of the lack of 
sufficient supplies of Rope. In a large number 
of cases they were successful and some of the 
bogey of low-altitude missions to the well- 
defended Shimonoseki Straits and Inland Sea 
areas was dissipated. Rope was sometimes em- 
ployed by aircraft on weather strike missions 
which carried RCM observers and by the B-24 
Ferrets to stir up radar activity on the part of 
the Japanese so that more signals could be 
heard and analyzed during a given mission. 
Dispensing of Rope usually brought many 
radars on the air to have a look at the disturb- 
ance. 

Miscellaneous 

Perhaps the most important contribution of 


the countermeasures war on the ground came 
in the AJ training phase for radar operators. 
The most obvioul and certainly the first anti- 
jamming measures to be taken with any type 
radar set involved the proper training of its 
operators and a recognition of the various 
forms of interference and deception to which 
it might be subjected. On a small scale, organ- 
ized training activity was carried out in the 
field prior to mid-1943 ; before this time a cer- 
tain amount of AJ instruction had been given 
in the United States, but this was of a very 
general nature. With the arrival of substantial 
quantities of aircraft in the Hawaiian area, 
late in 1944, the then newly formed headquar- 
ters of the Army Air Forces, Pacific Ocean 
Areas, assisted in a training program already 
under way in the Hawaiian group as a joint 
endeavor between the Army Signal Corps and 
the Navy. The AAFPOA Electronics School, an 
Army Air Force organization, originally de- 
signed to instruct operators of purely counter- 
measures equipment, found that a great part 
of its facilities and effort could best be directed 
toward the training of radar crews in AJ tech- 
niques. Accordingly, classes were scheduled for 
each of the Army units operating in that local- 
ity and whenever possible for all similar groups 
using it as a staging area for shipment to the 
forward area. In addition to classroom lectures, 
demonstrations by weekly exercises were held 
and, with simulated attacks, were executed in 
close approximation to the Japanese tactics as 
they were known then. Window and Rope for 
1-f early warning, as well as microwave search- 
light and fire-control equipment, received the 
greatest emphasis. Electronic jamming and de- 
ception were utilized on a somewhat smaller 
scale. Beyond the value of teaching operators 
AJ techniques and the operation of counter- 
measures equipment, these exercises served as 
a final proving ground for certain tactical doc- 
trines which previously had been no more than 
suggestions. For each jamming exercise, the 
battle plan was drawn with special tactical ob- 
jectives. As the execution proceeded, members 
of an Army-Navy planning staff were present 
at the fighter-direction-control boards and the 
filter centers. Afterwards there would be a 
critique for each exercise which would attempt 


366 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


to evaluate the success of the mission. This was 
particularly useful at a time when both Navy 
and Army Air Forces doctriifts for combat use 
of countermeasures equipment were still being 
formulated. 

Many violations of security on plane-to-plane 
v-h-f conversations were being observed early 
in 1945, and at the request of the Commanding 
General of the 73rd Bomb Wing (21st Bomber 
Command) the RCM organization within the 
wing began a program of monitoring and re- 
cording Channel C, the plane-to-plane v-h-f 
frequency. This job fell to the RCM personnel 
merely because they were the only ones who 
possessed recording equipment suitable for 
doing this work. Usually several planes in the 
wing were equipped with receivers and record- 
ers and continuous records of all v-h-f conver- 
sations in the target area were made and the 
violations of security observed were presented 
in group and wing critiques. The practice of 
recording plane-to-plane very high frequency 
spread to other wings and became common 
practice throughout the Twenty-first Bomber 
Command. The program resulted in a marked 
decrease in security violations over the target 
area and after an initial several months was 
continued on a considerably smaller scale. How- 
ever, even this required too much of the time 
of the RCM organization, which by this time 
was busy with the offensive countermeasures 
program. The responsibility of v-h-f monitoring 
for security purposes was finally transferred 
to the radio officer in each group. ANQ-2 disk 
recorders which were being little used for RCM 
purposes were supplied by the RCM organiza- 
tion for this work. 

An ambitious RCM indoctrination program 
was set up within the Twenty-first Bomber 
Command for the main purpose of teaching 
high-level staff personnel the capabilities and 
limitations of radar countermeasures. In addi- 
tion, one phase of the program involved actual 
offensive operations against U. S. radars in the 
Marianas chain, mostly for demonstrating to 
flight crews and staff personnel what the capa- 
bilities and limitations of RCM were. This 
phase of the program lost some of its impor- 
tance after the use of offensive countermeasures 
over the Japanese Empire gave the same results. 


At the request of Marine Corps units, which 
operated most of the EW and fire-control radar 
equipment in the Marianas, B-29's were sup- 
plied for Chaff-dropping exercises. Rope and 
Chaff, supplied mutually by Marine Corps units 
and Air Force units, were used for practice 
missions against EW, GL, and SLC radars. 
RCM officers from the Twenty-first Bomber 
Command were stationed at the radar sites as 
observers during these exercises and gained 
valuable experience in what to expect from 
their own use of Chaff and Rope. The Twenty- 
first Bomber Command was assembling a stock- 
pile of S-band Chaff, both for insurance pur- 
poses and for training exercises of this type. 

Effectiveness of the RCM Program 

The evaluation of the effectiveness of an 
offensive RCM program is a difficult task at 
best. The tactics employed by the B-29’s were 
fluid and changing continually, and comparison 
of flak losses before and after the advent of 
offensive countermeasures was impossible. At- 
tempts to compare flak damage of light squad- 
rons which had poor barrages, because of for- 
mation difficulties, with those which had good 
barrages, gave no significant result. Although 
no quantitative figure can be stated as being 
the reduction in flak losses attributable to the 
use of RCM, it was known from specific in- 
stances that the RCM was effective in some 
cases. A large number of instances of success- 
ful searchlight evasions when Rope was em- 
ployed are on record. These successes achieved 
for the most part with the elementary deceptive 
tactics used indicate that the Japanese radar 
operator was an easy one to fool. As long as the 
Rope was dispensed before the aircraft was 
actually coned, the success of this tactic was 
excellent. Similar evasions of flak through 
undercast by the use of Rope were reported 
and, in a number of cases where electronic 
jamming was employed, searchlights were re- 
ported to have searched around wildly, never 
finding a plane. In a number of instances, spot- 
jamming operators observed that radars would 
go off the air when jammed, and “cat and 
mouse^’ tactics were often engaged in by the 
spot-jamming operators and the enemy radars. 
In some cases, flak would cease or searchlights 


RCM IN THE GROUND FORCES 


367 


would be extinguished when the radar signal 
locked on the aircraft carrying the observer 
was spot- jammed. On several night strikes in 
which Porcupines were used, flak oflicers felt 
that the lack of serious flak damage was due 
for the most part to the effect of the offensive 
RCM on radar-controlled searchlights. The 
point was reached in some cases where wing 
operations officers insisted upon the use of 
Porcupines even though the RCM officer did not 
feel that they were necessary for the particular 
mission in question. It can be said that RCM 
had sold itself to the majority of the operations 
personnel in the Twenty-first Bomber Com- 
mand. Thus, an accumulation of evidence of 
this kind indicates that the offensive RCM effort 
produced some good results, even though a 
quantitative statement of flak loss reductions 
cannot be made. 


RCM IN THE GROUND FORCES 

RCM activities by Army ground force units 
in the Pacific areas were limited in extent. Brief 
mention of the AJ training activities has been 
made under the heading ‘‘Miscellaneous'^ in 



Figure 13. Ground-jamming installation (100 
me) for Beaver I mission, Bird Cape, Amchitka. 


Section 15.6.6 in connection with the activities 
of the AAFPOA Electronics School. The rela- 
tively great distances between Allied-held ter- 
ritory and future Japanese-held targets made 
ground-based jamming activities, such as those 


carried on by Beaver III in the Mediterranean, 
impossible. Three Beaver missions operated 
during the course of the Pacific war, one in the 
Aleutians, and the other two in the Western 
Pacific Area. The major purpose of the three 
Beaver missions in the Pacific area was that 
of reconnaissance, and, although they were 
equipped with jamming equipment, it was never 
used. It should be pointed out that although 
Beaver IV and V were Army ground force 
units, they were under the operational control 
of AAFPOA. 

In August 1943, Beaver I, a platoon of Army 
Signal Corps personnel, operated a ground- 
based search position on the island of Amchitka 
and was prepared, if necessary, to jam the dual 
early-warning installation on Kiska. Based on 
the investigations of the first Ferret aircraft in 
the Aleutians, it was known that two Mark I 
Model 1, 100-mc, early-warning radar sets were 
located at an elevation of 525 ft on the shore of 
Kiska Harbor immediately behind the Japanese 
main camp area of Kiska. No other radars were 
found to be operating in the entire Aleutian 
chain. Since Mark I Model 1 radars had been 
captured previously at Guadalcanal and Attu, 
the effectiveness of previously developed jam- 
ming equipment against this particular radar 
was well known and thoroughly successful. It 
was a fortunate geographical occurrence that 
the island of Amchitka had a 750-ft plateau on 
its western tip, 52 miles distant from the enemy 
radars, almost exactly the limit of a direct 
transmission path. Technically it appeared pos- 
sible to deny the Japanese the use of their two 
early-warning radars by the use of properly 
sited previously developed jamming equipment, 
AN/APT-3 plus AM-14/APT. 

Upon receipt of a request that facilities be 
made available for countering the Kiska radars, 
a platoon of 40 men and 3 officers (part Army, 
part Navy) , known as the First Signal Service 
Platoon Special, was hurriedly organized and 
supplied with laboratory prototype equipment 
from the Radio Research Laboratory and with 
a civilian technical observer. The unit proceeded 
to Bird Cape, Amchitka, set up its equipment, 
and prepared for operations either as a ground- 
based radar search or jamming installation. 
With the completion of plans for the invasion of 


368 


RCM IN THE PACIFIC THEATERS OF OPERATIONS 


Kiska, it became apparent that landings should 
most properly take place on remote portions of 
the island in a region already blind to the enemy 
radar. The jamming transmitters could possi- 
bly have been used to deceive the enemy by 
jamming a sector quite far removed from the 
region of actual assault. On August 4, however, 
11 days prior to the landings, it was evident 
from aerial photographs that the Japanese had 
voluntarily demolished both radar sets. The 
mission was completed without the use of jam- 
mers by keeping a careful watch to determine 
that no new enemy radar came into operation. 

By the first of 1945, plans for the invasion 
of Iwo Jima and Okinawa had become definite. 
The state of the countermeasures war was far 
advanced by this time and it was realized that 
offensive countermeasures from the ground- 
based site would play only a minor role in the 
Pacific war. Allied knowledge of enemy radar 
had grown tremendously. Enemy communica- 
tions, always relatively well known, had begun 
to increase the knowledge of the tactics and 
doctrines behind the use of the Japanese radar. 
Quite strikingly though, knowledge of enemy 
navigational aids was almost completely absent. 
The extensive direction-finding nets which the 
Japanese used to assist their aircraft in land 
ferry routes were suspected, but actually were 
known only as vague generalizations. The use 
of beacons or homing stations or possibly even 
of a navigational system similar to our own 
long-range radio-navigation system (Loran) 
was a complete mystery. Northwest of the 


Marianas, cutting diagnonally across the Nanpo 
and Nansei Shoto chains, there was a perpetual 
weather front which offered navigational prob- 
lems to the enemy as well as to the Allies. For 
the purpose of investigating primarily Japanese 
navigational aids, the First Signal Service Pla- 
toon Special was redeployed from Corsica to the 
Hawaiian Islands where it was put under Army 
Air Force control and split into two detach- 
ments, one destined for Iwo Jima, and the other 
for the northern tip of Okinawa. 

Each detachment was equipped with inter- 
cept receivers, and direction-finding antennas 
for the frequency range 0.5-1,000 me. Jamming 
equipment in the frequency range 100-200 me 
was also available. By June 1945, search opera- 
tions were under way which, if continued for a 
greater period of time, would have shown in all 
likelihood that the Japanese navigational aids 
were limited principally to ground-based and 
airborne direction-finding systems in the 3- to 
10-mc range, in addition to a few coded beacons. 

Mention should also be made of an Australian 
Army land-based intercept unit in the South- 
west Pacific Area. While its main function was 
radio intercept, it was on occasion in a position 
to provide valuable radar data. On December 
26-27, 1944, a Japanese naval task force bom- 
barded the Allied Mindoro beachhead. The in- 
tercept unit was located nearby, on Ilin Island, 
and by means of its APR-1 and DF-ing antenna 
was able to follow the force through all its ma- 
neuvers, obtaining invaluable information about 
the radars used for fire control, air warning, etc. 


Ol 


APPENDIX 


RECEIVERS 

PAGE 

1.1 Communications Search Receivers 371 

1.2 Radar Search Receivers 371 

1.3 Radar Early-Warning Receivers 375 

1.4 Direction-Finding Receivers 375 

1.5 Controlled-Device Receivers 380 

TRANSMITTERS 

2.1 Communications Jamming Transmitters 381 

2.2 Airborne Radar Jamming Transmitters 383 

2.3 Ground-Based and Ship-borne Communications Jamming Transmitters . 389 

2.4 Ground-Based and Ship-borne Radar Jamming Transmitters 390 

2.5 Expendable Transmitters 391 

2.6 Controlled-Device Jamming Transmitters 392 

2.7 Miscellaneous Jamming Transmitter Studies 393 

ANTIJAMMING 

3.1 Communications Antijamming 395 

3.2 Radar Antijamming 403 

DECEPTION AND CONFUSION DEVICES 

4.1 Mechanical Deception and Confusion Devices 408 

4.2 Electrical Deception and Confusion Devices 412 

TEST AND TRAINING EQUIPMENT 

.1 Signal Generators 413 

.2 Spectrum Analyzers 415 

5.3 Frequency Meters 417 

5.4 Miscellaneous Test Equipment . 418 

5.5 Training Equipment 420 

RCM EQUIPMENT 

6.1 Electron Tubes 422 

6.2 Ultrahigh Frequency Oscillators 425 

6.3 Effectiveness of Various Types of Modulation 429 

6.4 Antennas 433 

6.5 Coaxial Cable, Wave Guides, and Fittings 446 

6.6 Noise Sources and Studies 448 

6.7 Miscellaneous Research and Development 452 

RCM APPLICATIONS 

7.1 Airborne RCM Systems 456 

7.2 Operational Considerations and Tests 456 
















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RECEIVERS 

COMMUNICATIONS SEARCH 
RECEIVERS 

895-22 (RP-325) ( J. B. Atwood, G. E. Hansell) . 
Describes a method for identification of pulse com- 
munication systems in enemy use. The necessary 
equipment consists of a pulse receiver having an 
adjustable automatic gain control system and low 
impedance output to either a scope for visual ob- 
servation of pulse length and type of modulation 
or to a detector and audio amplifier for aural obser- 
vation of the average pulse rate as determined by 
aid of a 5- to 250-kc oscillator. The report includes 
descriptions of the usual types of pulse communica- 
tion systems and tells how they can be recognized. 

(May 15, 1944) 

1045-1 (RP-991) (J. M. Hollywood). Discusses 
and specifies changes in SCR-522A to minimize 
pulse interference from Frey a EW stations, which 
operate on communication channel frequencies used 
by Allied fighter aircraft. Nine simple changes in 
the receiver circuit suffice to enable reception of a 
ground station until within perhaps 3 miles of a 
Freya. 

(November 16, 1943) 

1045-8 (RP-991) (G. P. McCouch). Discusses 
and specifies changes in BC-639A to reduce pulse 
interference from friendly radars operating near 
this ground receiver. The chief change is to add 
a double-triode limiter to clip the pulses to a level 
permitting speech to be distinguished. 

(May 17, 1944) 

1045-MR-l (M. T. Lebenbaum) . Describes modi- 
fications of H oilier after S-27D receiver to cover the 
17- to 28-mc band. This is accomplished by sub- 
stituting new coils for those normally used for the 
82- to 143-mc band. 

(August 2, 1944) 

1045-MR-7 (D. K. Reynolds). Describes an ex- 
perimental model for a 27- to Jf-S-mc panoramic 
receiver to display a band of enemy signals on a 
cathode-ray tube for accurate adjustment of a jam- 
ming transmitter. Frequency readings may be read 
directly to within 100 kc with discrimination of 
signals separated by as little as 50 kc. The display 
includes signals down to a level of 10 pv. The 
frequency to which an associated S-27 receiver is 
tuned is indicated by a strobe marker on the 
cathode-ray trace. 

(May 16, 1945) 

1138-1 (RP-307) (J. I. Heller). Considers the 


factors which affect the electronic tuning of fre- 
quency-modulated oscillators for panoramic recep- 
tion. The purpose is to 'aid in the design for 
maximum width and linearity of sweep. Results are 
tabulated for tests of five oscillators tunable over 
the 0.86- to 100-mc range, constructional data being 
given for each. 

(March 8, 1944) 

1138-2 (RP-307) (J. I. Heller, 0. Friedman). 
Derives formulas for the parameters of phase net- 
works using reactor tubes. The formulas are applied 
to finding the phase network resistor (2,000 ohms) 
and coil inductance (2.62 ph) for a Type 955 oscil- 
lator tube and 6AC7 reactor tube to provide maxi- 
mum sweep at a center frequency of 23 me. 

(October 23, 1944) 

1138-3 (RP-307) (J. I. Heller). Tells of unsuc- 
cessful experiments in extending the tuning range 
by means of electronic tuning for panoramic recep- 
tion. Although reactor tubes will extend the range, 
they have a low Q in the amplifier stages. 

(December 1, 1944) 


12 RADAR SEARCH RECEIVERS 

Airborne Receiver, 40-3,300 me, 2-mc Output Band- 
width. 

Div. 15 RP-144 Army AN/ APR-1 

RRL D-1003 Navy AN/APR-1 

Unit construction superheterodyne with four in- 
terchangeable plug-in tuning units to cover fre- 
quency range in four bands, an i-f amplifier unit, 
and a power unit. The receiver is an improved 
version of SCR-587 (ARC-1), which it is designed 
to replace. Various tuning units for manual opera- 
tion and automatic searching with or without sector 
sweep are described later in this section. 

411-TM-73 (D-1901, RP-381) (J. M. Pettit). 
Modification kit for i-f gain control and AVC 
switch for SCR-587 and ARC-1. 

411-TM-75 (D-1903, RP-381) (J. M. Pettit). 
Conversion for operation of ARC-1 receiver from 
a 28-v power source. 

411-TM-92 (C. M. Daniell and M. J. White). 
Airborne antennas for AN/APR-1 (see Section 6.4, 
M-313 and M-2101). 

411-TM-15 (J. M. Pettit). Brief description, 
parts list, and assembly drawing for variable-range 
motor drive. 

411-148 (D-2600, RP-462) (M. T. Lebenbaum). 
Modifications of AN/APR-1 to adapt it for use in 


371 


372 


APPENDIX 


setting transmitters for spot-j amming. The changes 
reduce the bandwidth from 2 me to about 0.5 me 
and reduce the sensitivity of the i-f amplifier by 
about 20 db. The report includes curves of amplifier 
response before and after modification. 

411-TM-43 (D-514) (J. M. Pettit). Illustrated 
description of wide-band (9 me or 0.6 me) i-f 
amplifier for AN/APR-4, 40-3,300 me, choice of 
bandwidth, otherwise same as AN/APR-1 except 
for added stage of video amplification. 


Type D-101 Tuning Units for AN/APR-1 and 
SPR-1 Receivers, Frequency Range 75-300 me, 
Single-Dial Tuning. 




Motor 

Motor drive with 


Manual 

drive 

adjustable sector 


tuning 

28-v, d-c 

sweep 

RRL 

D-lOl-C 

D-lOl-A 

D-lOl-D 

Army 

AN/TN- 

TU-58B 

AN/TN- 


2/APR-l 


17/APR-4 

Navy 

AN/TN- 

AN/TN- 

AN/TN- 


2/APR-l 2A/APR-1 17/APR-4 

411-6 (D. B. Sinclair). Operating instructions for 
type D-101 tuning units. 

411-TM-74 (D-1902). Motor-noise filter for TU- 
57B and TU-58B tuning units for SCR-587. 

411-TM-84 (Robert R. Buss). Temporary con- 
version of TU-57B and TU-58B to sector sweep. 

411-TM-141 (F. J. Kamphoefner) . Illustrated 
description and explanation of D-1905 (RP-381) 
spurious response indicator. The device consists of 
an externally actuated lever arm to be attached to 
the hinge end of the tracking cam for the butterfly 
tuners in the mixer and oscillator circuits inside the 
tuning unit. The arm detunes the mixer but not 
the oscillator, thereby enabling true responses to be 
distinguished from spurious responses due to strong 
signals. The device may also be used for checking 
alignment. 


Type D-102 Tuning Units for AN/APR-1 and 
SPR-1 Receivers, Frequency Range 300-1,000 me, 
Single-Dial Tuning. 



Manual 

tuning 

Motor 
drive 
28-v, d-c 

Motor drive with 
adjustable sector 
sweep 

RRL 

D-102C 

D-102a 

D-102D 

Army 

AN/TN- 

3/APR-l 

TU-57B 

TN-18/APR-4 

Navy 

AN/TN- 

AN/TN- 

TN-18/APR-4 


3/APR-l 3A/APR-1 


411-17 (D. B. Sinclair). Operating instructions 
for Type D-102 tuning units. 

411-TM-74 (J. M. Pettit) . Tuning units for SCR- 
587 and motor-noise filter for TU-57B and TU-58B. 

411-TM-84 (R. B. Buss). Temporary conversion 
of TU-57B and TU-58B to sector sweep. 

411-TM-141. Already described in this section. 

411-16 (D. B. Sinclair). Operating instructions 
for Type D-104 tuning units for AN/APR-1 and 
SPR-l receivers, frequency range 38-95 me, single- 
dial tuning. 




Motor 

Motor drive with 


Manual 

drive 

adjustable sector 


tuning 

28-v, d-c 

sweep 

RRL 

D-104C 

D-104A 

D-104D 

Army 

AN/TN- 

TU-56A 

AN/TN- 


1/APR-l 


16/APR-4 

Navy 

AN/TN- 

AN/TN- 

AN/TN- 


1/APR-l lA/APR-1 16/APR-4 


Microwave Tuning Unit for AN/APR-1 and 
SPR-1 Receivers, 1,000-3,100 me. 

Div. 15 RP-212 
RRL D-1500 

This development of an improved tuning unit for 
use with D-1003 or D-1005 receivers employs a 
special short model wide-range oscillator (GL-446 
in coaxial line) ganged with a tuned mixer so as to 
provide single-dial tuning. An adjustable antenna 
input line permits setting for maximum sensitivity 
at any one frequency. 

411-TM-49 (J. M. Pettit). Preliminary descrip- 
tion and specifications for D-1500 including state- 
ments as to ease of tuning and freedom from 
spurious response. 

411-11. Detailed description of A-1501 oscillator. 

411-TM-85 (P. J. Sutro). Technical information 
and drawings for A-1503Q oscillator, an improved 
version of A-1501 as regards simplicity of construc- 
tion and operation. * 

Airborne Search Receiver, 1,000-3,100 me. 

Div. 15 RP-135 Army AN/ APR-5 

RRL A-2600 Navy AN/ APR-5 

Single-dial superheterodyne whose local oscilla- 
tor is a GL-446 “lighthouse” tube in a special 
double coaxial cavity (A-1501, see Section 6.2^ and 
whose mixer is a crystal. The beat frequency, de- 
rived from the fundamental frequency of the local 
oscillator, is fed to a wide-band (10 me) i-f ampli- 
fier centered on 30 me. The d-c component of the 
second detector voltage is amplified and observed 
on a panel meter indicator of unmodulated signals. 
General characteristics of modulated signals are 


RECEIVERS 


373 


determined from audio output to headphones. 
Pulsed signals are analyzed by aid of AN/APA-6 
or AN/APA-11 as auxiliary equipment connected 
to video output. The receiver has a sensitivity of 
50pv from a 70-ohm source and the tuning dial 
accuracy is within it: 1 per cent. 

411-40 (R. B. Holt). Detailed description, block 
and circuit diagrams, and photos. 

411-TM-137 (G. E. Hulstede). Suggestion that 
the frequency range of A-2600 can be extended to 
4,500 me or higher by using harmonics of the beat- 
ing oscillator. Ambiguities due to harmonic re- 
sponses can be completely eliminated by switching 
filters in and out of the antenna leads. The filters 
would include a low-pass cutting off at about 
2,000 me to eliminate second and third harmonics, 
and a 2,300- to 4,000-mc band pass to eliminate 
oscillator fundamental frequencies. 

411-143 (Q-1600, RP-286) (W. H. Huggins, 
J. J. Wedel). Discusses two methods for blanking 
AN / APR-5 in order to suppress the interference 
produced by a local radar system. Both methods 
require a “trigger” pulse from the radar to actuate 
an auxiliary blanking circuit. In one method the 
radar pulse actuates the generation of a well-defined 
adjustable positive pulse for blanking the cathodes 
of two r-f amplifier tubes. In the other method the 
radar pulse actuates the generator of a negative 
pulse for blanking the suppressor grids. Either 
method is feasible and only requires an auxiliary 
circuit to be installed in a small box attached 
to the receiver. Preliminary tests indicate that 
suppressor-grid blanking is somewhat preferable 
and completely effective in eliminating the inter- 
ference. The report includes circuit diagrams and 
performance curves. 

411-144 (Q-1600, RP-286) (W. H. Huggins, 
J. W. Kearney) . Discusses the theory and practice 
of using a pulse stretcher to provide greater audio 
sensitivity for a search receiver. The method em- 
ploys a diode and RC circuit between the video and 
audio amplifiers to convert a short pulse into a long 
one which dies away exponentially at a rate deter- 
mined by RC, for which an optimum value is 
calculated for a given pulse-repetition frequency 
[prf]. No more tubes need be added to the receiver. 
The method, which is that applied in TMR-llT, 
nearly doubles the audio sensitivity and increases 
the audio power output due to a pulsed signal by as 
much as 20 db. 

411-152 (R-1000, RP-107) (T. E. Moore, W. G. 
Wadey). Presents graphs of characteristics of 
AN / APR-5 A as measured by methods which are 


discussed at some length. The chief characteristic 
shown is the minimum detectable signal, both visual 
and aural, as a function of frequency for three 
different mixers. Others include plots of audio out- 
put power versus r-f input power at various gain 
levels, video output voltage versus r-f input power, 
audio output power versus crystal current, audio- 
frequency response, and overall gain. 

411-230 (W-1500) (J. M. Moran, Geo. Kolstad). 
Discusses operation and performance of “Silent 
Knight,” a blanking circuit that permits a search 
receiver to listen through an adjacent radar operat- 
ing in the same frequency band. Laboratory and 
flight tests demonstrated that SCR-717 signals can 
thus be eliminated from AN/APR-5 less than 10 ft 
away. The circuit uses the positive trigger pulse 
from the SCR-717 modulator to form a delayed 
pulse. This is applied to the suppressor grids of the 
first three i-f stages in APR-5 (or APR-4) in order 
to blank the received radar pulse. 

Airborne Search Receiver, 3,000-6,000 me. 

Div. 15 RP-291 Army AN/APR-6 

RRL A-2700 Navy AN/ APR-6 

Differs from airborne search receiver, 1,000-3,100 
me, only in r-f parts. The antenna-mixer assembly 
is a wave guide; beat frequency is derived from 
second harmonic of local oscillator. 

411-40 (R. B. Holt). Detailed description, block 
diagram, circuit diagram, and photographs. 

411-TM-71 (W. G. Wadey). Information on in- 
stallation of wave guides. 

411-TM-44 (RP-286, R-1800) (R. C. Raymond). 
A modification of the obsolete SCR-535 identifica- 
tion friend or foe [IFF] set to permit the recording 
of received signals on a frequency and time chart. 
The SCR-535 is essentially a transceiver containing 
two superregenerative receivers which alternately 
sweep small frequency bands in the 100- and 
200-mc regions. The sweeping action is accom- 
plished by rotating condensers driven from a gear 
train on one end of the dynamotor. The set is 
modified by (1) substituting a recording mechanism 
for one of the receivers and its diode rectifier, (2) 
changing the other receiver to sweep the 550- to 
600-mc band, (3) applying the pulse to the recorder 
instead of retransmitting it. The recorder is me- 
chanically operated by the mechanism previously 
used to rotate the sweeping condenser. 

411-IB-49. Illustrated description and prelimi- 
nary instructions for installation, adjustment, op- 
eration, and maintenance of AN/APR-7, D-2100 


374 


APPENDIX 


“Spud” search receiver, 1,000-3,500 me, with tuned 
detector and A-2608/A-2612 antennas. 

411-IB-49A. Supplementary instructions on 
D-2105 untuned detector kit to be used with 
D-2100. 

Single Signal Receiver 2,000-4,000 me and 6,670- 
10,900 Me 

Div. 15 RP-435 

RRL K-2000, K2100, Q-2100 
This partly developed receiving system is de- 
signed to reduce or eliminate image and other 
spurious responses. An image rejection of at least 
30 db is accomplished by using three stages of 
200-mc i-f amplification. The 2,000- to 4,000-mc 
range is covered by means of a tuned cavity oscil- 
lator (RP-286, Q-1600) using a type 2K28 tube. 
The 6,670- to 10,900-mc range is covered by a 
modification of Q-1200 for a 20-mc bandwidth. Pre- 
selection is provided by a Q-1900 multiple cavity 
tunable r-f filter. The system is designed for use 
with a K-2000 panoramic-presentation unit. 

411-259 (S. B. Cohn). Describes and discusses 
the Q-1900 (RP-442) preselector. 

411-268 (Q-1248, RP-286) (H. M. Zeidler, 

L. Manning, T. E. Moore) . Discusses the electrical 
characteristics of reflex klystron local oscillator to 
be used in superheterodyne receivers for the 6,600- 
to 10,700-mc range. The oscillators are coaxial sys- 
tems using type 2K48 tubes. The tuning device is 
a resonant noncontacting plunger having low-Q 
slots to suppress circumferential resonances in the 
plunger gaps, thus assuring operation free of noise. 
Initial tests indicate that simple end-point align- 
ment of the oscillator drive and of the reflector- 
voltage tracking systems will provide satisfactory 
receiver calibration and operation. 

Airborne Recording Unit for D-1005, AN/APR-1, 
AN/APR-4, or other Search Receiver. 

Div. 15 RP-276 Army AN/APA-23 

RRL D-1800 Navy AN/APA-23 

Unit provides permanent tape record of frequen- 
cies and reception times for all received pulsed or 
other modulated signals. The tape and a marking 
stylus are driven by a motor which also synchro- 
nously drives the receiver’s tuning dial through a 
selected portion of its range. The stylus periodically 
traverses the width of the tape and makes an elec- 
trochemical mark thereon whenever it is actuated 
by a signal impressed through the video output of 
the receiver. The tape is likewise marked at 1-min 


intervals along its length by a timing mechanism 
actuated by an 8-day clock. Signal frequencies are 
determined by means of a calibrated scale applied 
over the tape record. 

411-TM-50, 50A, SOB (H. E. Overacker). De- 
tailed description, pictorial drawing, and circuit 
diagram. 

411-173 (AV-1300, RP-276) (R. E. Anderson). 
Flight tests of the AN/APA-23 recorder with a 
companion AN/APR-4 receiver against four radars 
ranging in frequency from 106 to 567 me demon- 
strated that (1) the maximum distance at which 
signals were recorded for an altitude of 5,000 ft was 
70 miles for the SCR-268 and 125 miles for the 
SCR-271, (2) the maximum response spread was 
17 me against the SCR-648, which is not excessive, 
and (3) the electrical and mechanical performance 
of the recorder was entirely satisfactory during all 
the flight tests. The report gives complete illustrated 
information about the equipment, test apparatus, 
and tests. 

“Autosearch” Airborne Receiver for Automatically 
Indicating and Recording Frequencies of Received 
Signals in the Range from 90 to 1,000 me. 

Div. 15 RP-139 Army AN/APR-2 (RC-160) 

RRL C-1100 Navy AN/ APR-2 (CXCS) 

Indication is by headphones, by a flashing neon 
bulb behind a slot in the panoramic dial, or by a 
tape record having correlated time markings. The 
frequency range is covered in two continually swept 
bands (90-420 me and 420-1,000 me) by two tuned 
(“butterfly”) circuits with separate antennas. The 
entire frequency range is swept either two or six 
times per second. The r-f signal voltages are de- 
tected by crystals in each circuit and amplified by 
separate high-gain video channels. The amplifier 
outputs are commutated to amplifier trigger circuits 
in proper relationship to give continuous rapid 
coverage and presentation. 

411-13 (E. L. Plotts). The RC-160 receiver 
(Autosearch) . 

411-132 (P. A. Pearson). Description of modi- 
fications for improving performance of APR-2. 
These include (1) installation of automatic gain 
control to prevent excessive spreading of dial and 
recorded presentation by strong signals, (2) capaci- 
tive shunting of lawnmower brushes to eliminate 
interference from time-marker clicks, and (3) using 
a fixed voltage divider instead of potentiometer for 
bias of gas tube, thereby eliminating an unneces- 
sary control. 


RECEIVERS 


375 


» 3 RADAR EARLY-WARNING 

RECEIVERS 

Zero Catcher II, 350-700 me. 

Div. 15 RP-287 
RRL R-800 

Equipment includes three separate r-f and pre- 
amplifier units whose outputs are handled simul- 
taneously by a three-channel a-f unit to operate 
neon warning lights and/or to provide a warning 
signal on the interphone circuit. There is also a 
power-line filter unit to remove ripple and hash 
from the 28-v d-c supply. Each r-f and preamplifier 
unit consists of an antenna, low-pass coaxial filter 
with sharp cutoff at 1,200 me to prevent interfer- 
ence from 10-cm radar aboard craft, resonant-line 
r-f tuner, diode or crystal detector, and two-stage 
a-f amplifier. Two of the units are used for right 
and left tail warning of German AI and the third 
for warning of German GL, SLC, or GCI. Their 
outputs are fed simultaneously to the three-channel 
a-f unit, two of whose channels operate the warning 
lights and/or signal and the third is equipped with 
adjustable time delay to prevent warning by signals 
from nontracking radars. 

411-TM-lll (S. B. Cohn). Briefly describes 
equipment, explains operating principles with aid 
of block diagram, and gives specifications. 

411-TM-64 (S. B. Cohn). Illustrates and de- 
scribes structure and characteristics of low-pass co- 
axial filter in 50-ohm line. 

411-52 (S. B. Cohn). Discusses various means 
for reducing interference from noise and hum in air- 
borne installations of RC-164 Zero Catcher. Hum 
was reduced by (1) the use of twisted pair shielded 
cable to carry the signal from the antenna to the 
receiver, with an isolating transformer at the an- 
tenna, (2) ungrounding the input circuit between 
the isolating transformer and the receiver, and (3) 
the insertion of an 0.1 -h filter choke in series with 
28-v d-c supply for the amplifier. Microphonic noise 
was reduced by substituting crystals for diode de- 
tectors, substituting a 9005 diode for the 9004 
detector, and mounting the antenna at a point 
where vibration is at a minimum. Ignition noise 
was eliminated by bonding and shielding. 

‘ ^ DIRECTION-FINDING RECEIVERS 

100-3 (RP-404) (W. E. Rife). Discusses tech- 
niques used in modeling DF loop antennas and 
results obtained for a B-24 aircraft in the simulated 
range of frequencies from 15 to 30 me. Measure- 


ment data are given for calibration curves showing 
loop bearing versus true bearing, radiation patterns 
of the rotating loop, and patterns for a loop fixed 
in various orientations as the aircraft rotates. The 
tests indicate that operation of DF loops can be 
satisfactorily predicted by measurement of models. 

(June 11, 1945) 

“Setter” Airborne Direction-Finding Attachment 
for Use with D-1003 or D-1005 in Covering Fre- 
quency Range from 100 to 750 me. 

Div. 15 RP-298 Army AN/APA-24 

RRL C-2100E Navy AN/APA-24 

Equipment covers frequency range by means of 
four interchangeable r-f heads (C-2110, 100-165 
me; C-2116, 165-275 me; C-2127, 275-450 me; and 
C-2145, 450-750 me), any one of which is rotated 
by single antenna mount and drive mechanism and 
each of which requires a separate balance converter 
and switch for selecting horizontal or vertical po- 
larization. The device operates on the principle of 
null signal and requires tw^o bearing observations to 
eliminate ambiguity as to direction of transmitting 
station. Accuracy of indication is approximately 
± 5 degrees. Each antenna assembly consists of a 
horizontal dipole and two vertical dipoles (Adcock) 
phased so that all four nulls lie on the axis of the 
horizontal dipole. The assembly is mounted on a 
driveshaft which is rotated by a hydraulic servo 
mechanism, remotely controlled. The null is ordi- 
narily detected by headphones; an oscilloscope is 
used for greater accuracy or to separate two sta- 
tions differing only in prf rate. 

411-TM-61,-61A,-61B,-61C (J. W. Christensen, 
R. L. Hammett, F. M. Wrightson). Complete de- 
scription and photographs. 

411-156 (W-500, RP-284) (0. W. Whitby). De- 
scribes flight tests of a modified APA-24 antenna 
with electric drive for bottom mounting. The elec- 
tric drive replaces the original hydraulic drive and 
the bottom mounting permits the antenna’s being 
retracted against the underside of a B-24. Results 
showed the superiority of the electric drive, but 
indicated the need for a better method of control- 
ling the antenna’s direction in order to realize more 
fully the freedom from error that results from 
bottom mounting. This might be provided by a sug- 
gested type of d-c servo system. The report recom- 
mends various improvements in the mechanical 
construction of the antenna and its mount. 

411-180 (W-500) (J. J. Wittkopf). Reports per- 
formance of modified AN/APA-24 on B-29 combat 
rnissions. The antenna was bottom-mounted with 


376 


APPENDIX 


manual retraction and modified for electric drive 
and interchangeability between aircraft. The report 
contains photos and drawings of modified equip- 
ment as installed and reproductions of 24 DF cuts 
on horizontally polarized Japanese radar systems 
operating in the 71- to 211 -me frequency range. 
Accuracy on the average intercept was found to be 
nearly comparable to the average navigational ac- 
curacy. The operating personnel was well pleased 
with the equipment. 

411-208 (W-1900, RP-298) (J. J. Wittkopf). 
Describes modifications of AN/APA-42 DF an- 
tenna to adapt it for bottom mounting in a B-29 
in accordance with recommendations in 411-180 
above. 

411-TM-61 (J. W. Christensen). Detailed de- 
scription and operating characteristics of ‘‘Setter’’ 
Direction Finder. 

Div. 15 RP-298 Army AN/ARD-3 

RRL C-2100 Navy AN/ARD-3 

Same as AN/APA-24 except for antenna heads 
and balance converters. Made in three models: 
C-2100A with fixed head (100-165 me), C-2100B 
with fixed head and short mounting strut (for use 
where space is limited) (275-450 me) , and C-2100C 
with two interchangeable heads (100-165 me or 
275-450 me) . 

“Fanny” Homing Attachment. 

Div. 15 RP-108 Army AN/APQ-14 

RRL C-1700 Navy AN/APQ-14 

This device may be used with any receiver and 
with an antenna system having a null forward and 
in line with the craft in which it is installed, to 
enable it to home on a received r-f signal. This is 
done by maneuvering the craft until the null of the 
antenna pattern coincides with the direction of the 
incident signal. Operation depends upon obtaining 
in headphones an a-f output which is proportional 
to i-f input. This is obtained by first feeding the 
receiver’s amplified audio output to a diode peak 
detector circuit having a time constant of i /2 sec. 
The d-c output is then used to change the bias of a 
6SJ7 used as a variable-resistance element through 
which a condenser is charged. The condenser is 
alternately discharged by a 2050 thyratron. Since 
the output frequency is a direct function of the 
value of the charging resistance, it is thus directly 
proportional to the intensity of the received signal. 

411-TMR-lO. Gives brief description, including 
changes made as result of field tests, instructions 
for installation, schematic diagram, and photos. 


411-30 (P. H. Reedy). Discusses principles of 
operation, including circuit and antenna details, in- 
structions on procedure for installation and opera- 
tion, and summarizes results of field tests. 

411-227 (W-2400) (J. J. AVittkopf). Flight tests 
of C-1906 indicated generally satisfactory perform- 
ance as regards accuracy and reliability. The de- 
termination of sense was easily accomplished. Great 
care is necessary in the selection and installation of 
the two antennas so as to insure physical and elec- 
trical symmetry. The report recommends that the 
audio level be raised to permit simultaneous moni- 
toring of communication channel and homing 
equipment. 

411-198 (J. W. Christensen). Describes and dis- 
cusses the C-1906 azimuth homing system as as- 
sembled for use in Navy-type F6F aircraft. The 
assembly comprises the C-1933 adapter unit, two 
C-1954 eightball antennas, modified AN/APR-1 
receiver, approach indicator, remote-control box, 
and various mountings. The C-1933 is a revised 
form of C-1900 with a two-channel r-f and video 
commutator, pulse-widening and amplifying cir- 
cuits, AVC and earphone circuits, integrating and 
bridge circuits, and a power supply. The antennas 
are mounted on the wings, with the control box and 
approach (cross-pointer) indicator in the cockpit, 
and the balance of the equipment in the fuselage. 
The report discusses the primary uses and limita- 
tions of the system as well as the theory and 
methods of operation. 

411-213 (J. AA^. Christensen). Describes a field 
measurement method for finding antenna positions 
and mountings that will yield satisfactory homing 
patterns with C-1954 (or other C-1950 series) 
antennas installed in various types of aircraft. Con- 
sideration of such factors as frequency range, pat- 
tern symmetry, crossover points, fore and aft sensi- 
tivity ratios, and balancing of antennas and cables 
demonstrates that various compromises are neces- 
sary to provide good sensitivity and good definition, 
and to eliminate ambiguous crossover points. Proper 
procedure is explained in detail. 

“Tail” Homing Attachment. 

Div. 15 RP-209 Army AN/APA-48 

RRL C-1900 Navy AN/APA-48 

This attachment used in connection with a suit- 
able receiver and antenna system enables a craft to 
home in both azimuth and elevation on radar, jam- 
ming, or communications signals. The attachment 
consists of a four-channel r-f switch, a four-channel 


RECEIVERS 


377 


commutator, four integrating circuits, and a cross- 
pointer output meter. The r-f switch successively 
connects the receiver to each of four antennas, one 
pair for azimuth and one pair for vertical indica- 
tion. The video output voltage of the receiver is fed 
back to the attachment, where it is sychronously 
commutated and applied to four integrating circuits 
having long time constants. The switching rate may 
be adjusted so as not to correspond to the lobe- 
switching rate of the enemy signal. Indication of 
right-left and up-down is given by a standard cross- 
pointer output meter. 

411-168 (J. W. Christensen). Discusses antennas 
and associated equipment used in v-h-j homing sys- 
tems. Results of flight tests show that a satisfactory 
system for eliminating enemy airborne and ground- 
based radars and jammers is provided by “sense- 
homing’’ with meter indication. The components of 
such a system, (antennas, lobe-switching receivers 
and attachments, indicators, and remote-control 
gear) are illustrated and described, with special 
emphasis on the design, construction, installation, 
and measurement of antennas. Flight results are 
summarized and details are given for a modified 
system (C-1905) for azimuth homing only. 

Airborne Direction Finder, 300-1,000 me, for Use 
with D-1003 or D-1005. 

Div. 15 RP-298 

RRL M-2300 

Equipment represents early developments lead- 
ing to AN/APA-17, but using oscilloscope with 
magnetic instead of electrostatic deflection. 

411-TM-46 (Arthur Dome). Preliminary speci- 
fications, explaining purpose, listing components, 
explaining principles of operation, and illustrating 
installation in plane. 

411-134 (Z-800) (J. D. Krays). Tabulates the 
various antenna spinner assemblies used in the 
M-2300, -2600, -3000, and -4100 DF systems, and 
charts the frequency range and application of each 
type. Sketches are given for the types which have 
been developed. 

411-TM-35 (P. L. Harbury). Illustrated descrip- 
tion and explanation of operating principle of all 
M-4500 spinners. Graphs show standing-wave ratio 
versus frequency for vertical and horizontal antenna 
gain of M-4502 dipoles over M-2414 dipole, and 
polarization discrimination ratios for horizontal 
and vertical antennas. Photos include typical pat- 
terns. These antenna heads extend the frequency 
range of the M-2300, M-2600, or M-3000 DF sys- 
tems so as to cover the 1,000- to 5,000-mc band. 


M-4502 is used with M-2300 and M-2600, M-4503 
with M-4100, and M-4504 with M-3000. They are 
identical except for mounting and relay details. 
Each consists of two rotational paraboloidal re- 
flectors mounted back to back on a 20-in. disk with 
a horizontal antenna assembly at the focal point of 
one reflector and a vertical antenna assembly at the 
focal point of the other reflector. Between the re- 
flectors is an r-f relay for selecting either one of 
the radiators. Each antenna consists of a balanced- 
sleeve dipole with a balun. The antenna pattern 
consists of a sharp symmetrical single lobe and 
small minor lobes. 

411-287 (E. C. Barkofsky). Describes the 
M-6600 antenna and drive assembly, discusses the 
factors influencing its general design and construc- 
tion, explains the theory of the horn as a radiator 
and receiver of circularly polarized signals, describes 
the steps involved in design for a specific frequency 
range, and presents performance curves. Brief in- 
structions are given for installation, operation, and 
maintenance. 

411 -IB-86. Instructs on the operation and main- 
tenance of M-6401 antenna spinner, 135-2,100 me. 
Div. 15 RP-138 Army AS-108B/APA-17 

RRL M-6401 Navy AS-108B/APA-17 

Designed as a component for M-3000, this spinner 
consists of a horizontal antenna and a vertical 
antenna, each supported by a reflecting sheet, 
mounted back to back with r-f relay between. It 
covers a wide frequency range with patterns suit- 
able for DF purposes. Except for a new injector box 
(M-4602), it is interchangeable with M-3001. 

Antenna Spinner System, 65-280 me. 

Div. 15 RP-298 Army AS-222/APA-17 
RRL M-6200 .Navy AS-222/APA-17 

This is one of a number of interchangeable 
spinner systems designed to cover various fre- 
quency ranges when used with AN/APA-17 
direction-finding equipment for obtaining bidirec- 
tional bearings on horizontally polarized signals. 
The antenna is a rotating double horizontal loop 
(M-6201) that is selsyn-tuned from a remote tuning 
unit (M-6202) , all operated from an M-6203 power 
supply through M-6204 cables. The antenna con- 
sists of two loops connected in opposition to give 
an 8-shaped pattern which is bisected through the 
maxima to obtain the bearing. 

411 -IB-90. Illustrated description and instruc- 
tions for installation, adjustment, operation, and 
maintenance of antenna spinner system. 


378 


APPENDIX 


411-IB-90A. Correction of minor errors in IB-90 
together with supplementary information and 
photos of patterns, to be used in search procedure 
with AN/APA-17. 

Ship-borne Direction Finder, 300-1,000 me. 

411-109 (J. D. Kraus, H. K. Clark, A. N. Mor- 
gan) . Description of installation and tests of CXGA 
on DE-239, using an APR-1 receiver to cover the 
frequency range. The equipment was found to be 
an inherently accurate form of direction finder. 
This broad-band DF system constitutes an adapta- 
tion of M-2300 to marine use with AN/SPR-1 re- 
ceiver. The receiver is fed by a rotating . antenna 
system which is polarized vertically and hori- 
zontally. The receiver output operates an oscillo- 
scope indicator (polar coordinate) of received signal 
strength (radially) versus azimuth of the antenna 
system. The apex of the pattern on the scope is 
thus at the bearing of the transmitter. 

411-TM-67 (P. L. Harbury) . Detailed illustrated 
description, with block and circuit diagrams and 
field patterns of homing device, aural or visual. 

Div. 15 RP-298 
' RRL M-3100 

This device used with a receiver provides a simple 
means for homing on an enemy radar system. It 
consists of two identical stub antennas, with an 
untuned reflector, an r-f relay, a motor-driven 
“A-N” cam, a phase inverter stage, and a power 
supply unit. The relay is connected so as to alter- 
nately switch the left-hand and right-hand antenna 
to the receiver input, being controlled by a micro- 
switch and the “A-N” cam. The rotating cam keys 
the signal from the left antenna with “A” and from 
the right antenna with ‘‘N” of the Morse code. 
When the two antennas receive signals of equal 
strength, the aural indication is a continuous tone 
in the receiver headphones. A visual indication is 
provided by aid of the inverter stage and an 
auxiliary cathode-ray oscilloscope which shows 
pulses in opposite polarities corresponding to the 
“A’’ and “N” indications. When several radars are 
operating simultaneously with different prf rates on 
the same frequency, the scope is synchronized to 
one prf, and “homing” is accomplished by matching 
the size of the stationary pulses. 

DBM Direction Finder, 90-5,000 me. 

Div. 15 RP-271 Navy DBM 

RRL M-4100 

This ship-borne, broad-band DF system, used 
with receivers covering its frequency range, pro- 
vides continuous indication of the arrival direction 


of radar pulses or continuous- wave [c-w] signals. 
It also indicates the frequency and polarization of 
received pulses, which may be further identified by 
means of an auxiliary pulse analyzer. The DF sys- 
tem consists essentially of two rotating directional 
antennas and an indicator unit containing a 
cathode-ray tube whose sweep circuit is synchro- 
nized with the rotation of the antenna. The relative 
bearing of a signal is found by bisecting the antenna 
pattern on the screen of the cathode-ray tube; this 
is translated to true bearing by means of a small 
gyrocompass repeater in the indicator unit. The 
antenna system consists of either one M-4101 
Type E spinner to cover the 200- to 100-mc range 
or one M-6120 Type M spinner (90-1,400 me) 
(Navy-type CFH66137) and one M-4503 Type H 
spinner (Navy-type CFH66137) to cover the 1,000- 
to 5,000-mc range. Each spinner is an assembly of 
a horizontal and vertical dipole and balun mounted 
with reflectors back to back. The spinners are inter- 
changeable on motor-driven shafts. The electro- 
static indicator permits instantaneous DF on sweep- 
ing signals and simultaneous DF on several signals. 

411-105 (A. W. Alford, W. D. McGuigan, J. Mar- 
golin, P. L. Harbury). Report of tests of M-4100 
system installed on USS Gunason, including discus- 
sion of installation problems. Results were generally 
satisfactory. 

411-181 (M-4130, RP-271) (E. C. Barkofsky). 
Describes conversion of AN/SPT-6 to a pulsed sig- 
nal source to be used for installation calibration of 
M-4100, and instructs on the installation, operation, 
and maintenance of the converted transmitter. The 
changes comprise replacement of the noise modula- 
tor by a pulse modulator consisting of a blocking 
oscillator type of pulse generator producing a 2-psec 
signal at a prf of 2,500 per second, rewiring the 
r-f oscillator to permit shock excitation from the 
modulator, new bleeder resistors and filter con- 
denser in power-supply section, and new antennas 
(AS-263/UPT and AS-236/SPT) to cover the 175- 
to 1,600-mc frequency range. The modified equip- 
ment has a peak power output of from 5 to 40 w, 
depending upon the r-f frequency. 

411-190 (W. D. McGuigan, E. C. Barkofsky, 
J. D. Kraus). Describes the procedure for cali- 
brating DBM-1 shipboard installations, including 
methods, signal sources, and precalibration checks. 
The calibration determines the deviations produced 
by the ship’s structure and checks the system’s over- 
all alignment. 

411-191 (J. D. Kraus, AV. D. McGuigan). De- 
scribes ship-borne tests of DBM direction finder. 

411-233 (J. D. Kraus, H. K. Clark, S. Bera- 


RECEIVERS 


379 


ducci). Describes the performance characteristics 
of the M-6120 broad-band antenna spinner. The 
report includes photos of observed antenna pat- 
terns over the 80- to 3,000-mc range. There are 
also curves of bearing deviation and sensitivity, as 
well as three-dimensional patterns. 

411-243 (M-6700, RP-271) (G. Stavis). Dis- 
cusses the design features of spinner. Its perform- 
ance is calculated from a theoretical explanation 
of the horn’s operating principle as a radiator and 
receiver of circularly polarized signals. The text is 
illustrated with photos, curves, and patterns, and 
includes an account of how DBM installations can 
be adapted to use this third antenna. Tests with an 
airborne radar as the signal course gave signal re- 
ception with the aircraft at a distance of 50 miles 
and an altitude of 1,000 ft. 

411-297 (H. K. Clark, W. W. McGuigan, C. A. 
Mizen). Illustrates and describes the submarine 
DF system, 2,300-4,600 me. 

Div. 15 RP-303 

RRL M-7100 

The equipment consists of a rotating directional 
antenna and an indicator unit to be used with an 
auxiliary receiver. The indicator unit is essentially 
a cathode-ray oscilloscope. The antenna consists of 
a vertically mounted horn whose mouth points 
downward to a rotating parabolic reflector making a 
45-degree angle with the horn axis. The horn has 
a circularly polarized response and the system has 
substantially equal response to vertical and hori- 
zontal polarization. The reflector is driven at 200 
rpm by a water turbine actuated by a jet from the 
pump room. The antenna drive is mechanically 
coupled to the rotor of a two-phase synchro which 
transmits antenna position data to the cathode-ray 
tube indicator. The synchro voltage is converted 
into a quadrature bias to four deflection amplifiers, 
one for each plate of the cathode-ray tube. Simul- 
taneously the antenna response is fed to the re- 
ceiver, whose video output is applied to the four 
amplifiers so as to deflect the narrow pattern in a 
direction corresponding to a given antenna bearing. 
The report discusses the reasons for adopting vari- 
ous components, explains calibrating procedure, and 
gives operating voltage data. 

‘‘Moth” Self-Guided Missile to Home on 90- to 
520-mc Radar. 

Div. 15 RP-188 Army AN/APQ-14 

RRL C-1600 Navy AN/APQ-14 

411-286 (C-1600, RP-188) (J. W. Christensen). 
Describes the Moth antennas and chassis developed 
for use with Glide Bomb, Pelican, and Glomb and 


describes flight tests in Pelican and Glomb, with 
graphic presentation of qamera records. Experi- 
ments with Glomb-Moth gave definite indication 
of target accuracies on the order of 10-25 ft. Esti- 
mates of Pelican-Moth accuracy place the figure 
at 50-150 ft. The equipment consists of a glider 
vehicle, carrying explosives, and equipped with an 
antenna array and a homing receiver. It is released 
from a large bomber at distances of 5 to 25 miles 
from the victim radar. The antenna array consists 
of dipoles which may be rotated to receive either 
vertically or horizontally polarized signals. The 
battery-operated superheterodyne receiver is re- 
motely tuned to the exact frequency of the victim 
radar before the vehicle is released by remote con- 
trol. The receiver is equipped with lobe switching 
and furnishes the control voltages to guide the 
missile. It has a 2-mc bandwidth and a sensitivity 
of about 50 pv. Several vehicles may be used, as 
follows: 


Wingspread (ft) 
Lb of explosive 
Support 
Type of control 


Pelican Dragon Glomb 


8.4 or 10 12 

500 or 1,000 3,000 

Carried Carried 

Automatic Automatic 
homing homing 


36 

2,000-4,000 
Towed 
Automatic 
homing, or 
television and 
radar homing 
repeat back 
with radio 
control 


936-4 (H. H. Buttner) . Describes tests to deter- 
mine feasibility of using Type-DBA direction 
finder on B-24J bomber. The DF equipment con- 
sists of a 1.5- to 30-mc superheterodyne receiver, 
cathode-ray tube bearing indicator, and rotating 
loop antenna. The results indicate a decrease in 
accuracy with increase in frequency, fading and dis- 
tortion at higher frequencies, and a high noise level 
at all frequencies. The report includes suggestions 
to overcome operating difficulties. 

(January 18, 1945) 

1045-12 (J. V. Granger). Describes the design 
features and constructional characteristics of a 
ground-based broad-band DF system consisting of 
four antennas to be mounted on a van equipped 
to detect and analyze radar or jamming signals. 
The antennas comprise 100- to 300-mc and 300- to 
1,000-mc horizontal thick dipoles and vertical 
Adcocks. The installation includes the mechanism 
for supporting and rotating the antennas. The re- 
port includes standing-wave ratio curves and direc- 
tional patterns. 

(April 23, 1945) 

1045-MR-9 (J. W. Keuffel, G. H. Klemm) . De- 


380 


APPENDIX 


scribes a daylight long-range (200-mile) fighter 
homing system {‘^Curtain”) for locating friendly 
or enemy aircraft or ground transmitters by homing 
on their 38- to 42-mc transmissions or on naviga- 
tional aid signals. The equipment designed for 
installation in a P-51B aircraft is a German 
ZVG-16 homing unit and FuGe 16Z receiver used 
with three modified AS-89/ART whip antennas, 
one for sense and one on each wing to form a 
grounded Adcock system with figure-8 pattern. The 
ZVG-16 compares two switched cardioid patterns 
obtained by switching the Adcock signal 180 de- 
grees in phase and adding the sense antenna signal 
to give the receiver input. The output is a 27-c sine 
wave whose amplitude is proportional to the dif- 
ference of the right and left antenna patterns and 
whose phase depends upon which pattern has the 
larger value in the direction of the incoming signal. 
The course indication is read from an I-lOl-C left- 
right meter in a balanced bridge circuit. A signal- 
strength meter is also provided to give rough indica- 
tion of the range of the target. 

(May 24, 1945) 

1045-MR-10 (G. P. McCouch). Describes the 
‘‘Judy’^ instantaneous DF system operating from 
vertically polarized 38- to 50-mc modulated or 
continuous-wave signals. Patterns of a double- 
Adcock antenna system and associated motor- 
driven goniometer are presented on a 5-in. cathode- 
ray tube. The patterns are given by the nulls of 
the goniometer responses and resemble a two- 
bladed propeller, being sharper than the indications 
obtained by presenting the antenna pattern directly. 
This first model contains no provision for sensing. 
Ground tests show an accuracy of it 4 degrees at 
40 me and it 6 degrees at 50 me. Satisfactory bear- 
ings were taken on an aircraft at 125 miles fiying 
at 15,000 ft with a radiated power of 3-w. The re- 
port includes brief instructions for operation and 
maintenance. 

(May 31, 1945) 

1045-MR-ll (M. B. Adams, G. H. Klemm). 
Describes trial installations, in three types of 8th 
Air Force day fighters, of the British ‘‘Perfectos” 
system for homing and ranging on German IFF 
airborne equipment (FuGe-25A). This system em- 
ploys a modified version of SCR-729-A beacon 
interrogator to trigger the FuGe-25A and give 
range and azimuth data on the responses. The 
apparatus consists of a pulsed transmitter operating 
on 125 me and a 156-mc receiver used with an 
antenna system whose characteristics are suitable 
for homing in azimuth. Received responses appear 
on the indicator scope of GEE navigation equip- 


ment. Preliminary operational results are encour- 
aging. 

(May 22, 1945) 

931-18 (RP-188) (H. Poritsky). Analyzes the 
effect of reflected radar waves on the path of a 
guided missile. The analysis is based on a theoreti- 
cal study of the interference field formed by two 
plane waves and of the equations for equilibrium 
orientation of an antenna system in that field. The 
general conclusion is that the missile will home in a 
wobbly path on a source of continuous radiation. 
For nonoverlapping pulses the path is more seriously 
disturbed until the missile gets close enough to 
be affected by the stronger amplitude of the 
source. 

(August 21, 1945) 

1458-2 (RP-445) (H. Busignies, T. H. Clark, 

H. B. Scarborough) . Describes a spinning loop air- 
craft direction finder for guided missile search in 

I. 5- to 22-mc range. Visual bearing indications with 
simultaneous monitoring of continuous-wave, inter- 
rupted continuous-wave, and keyed continuous- 
wave signals are provided by a cathode-ray tube 
indicator and a frequency scanner giving a 50-kc 
bandwidth on either side of the frequency to which 
the associated receiver is tuned. Operation consists 
in the selection of one of three plug-in loops for a 
desired frequency range, tuning the loop and re- 
ceiver, and interpreting the cathode-ray tube pat- 
terns. The report is essentially an instruction book 
on the tentative equipment. 

(September 29, 1945) 

CONTROLLED-DEVICE RECEIVERS 

1305-7 (905, RP-361). Instruction handbook for 
magnetic tape recorder AN/SRQ-2 to be operated 
from a standard receiver in order to monitor, record, 
or reproduce the control frequencies used in operat- 
ing guided missiles. This ship-borne model (Serial 
4, 5, and 6) gives a 1-min high-fidelity recording, 
has a response that is constant within 1.5 db from 
3 to 53 kc, and the recorded signal has a 35 db 
signal-to-noise ratio. When used with a S-36 Halli- 
crafter the 5.25-mc intermediate frequency is hetero- 
dyned down to 30 kc in the recording channel. 

(April 4, 1945) 

1305-9 (905, RP-361). Instruction handbook for 
magnetic tape recorder AN / ARQ-12 (Serial 1, 2, 
and 3). This is a lighter weight airborne model of 
the equipment described in 1305-7 and gives a 
15-sec recording. 

(June 5, 1945) 


TRANSMITTERS 


381 


1305-16 (905, RP-361) (R. A. Isberg, E. W. 
Adams). Describes the airborne Peter Pan system 
of jamming radio-controlled guided missiles by aid 
of magnetic tape recorders which are described in 
the report. The system is designed to receive, re- 
cord, play back, and retransmit enemy control 
signals in the 40- to 50-mc band. Most of the report 
is devoted to the theoretical and practical con- 
siderations which determine the design of magnetic 
tape recorders AN/ARQ-12 and AN/SRQ-2, as 
described in 1305-9 and 1305-7, respectively. 

(August 31, 1945) 

TRANSMITTERS 

21 COMMUNICATIONS JAMMING 
TRANSMITTERS 

89-1 (NDRC-58) (M. Cawain) . Describes a pro- 
posed communications interference generator, a 
modification of a MOPA transmitter circuit, to be 
used with a narrow-band panoramic search receiver. 
Interference with voice transmission in the 2- to 
20-mc band is provided by an alternate carrier sys- 
tem wherein the carrier frequency is randomly 
changed by means of code wheels. 

(May 1, 1942) 

89-2 (NDRC-58). Instruction book for inter- 
ference generator. 

89-3, -4, -5, -6, -7, -8 (NDRC-58). Progress 
reports from July 1941 to January 1942. 

778-2 (NDRC project C-63) (M. E. Campbell). 
Finds that the conversion of standard radio equip- 
ment to communication jamming equipment is gen- 
erally satisfactory. The presence of the transmitter 
carrier is advantageous and a communications re- 
ceiver may be used for searching. 

(November 11, 1942) 

285-1 (C-26) (A. Preisman). Describes the de- 
velopment of an interference generator with 50-w 
output in 15- to 30-mc range. Consideration of all 
requirements led to the construction of a model 
consisting essentially of a search receiver with 
cathode-ray tube presentation and a transmitter 
modulated with a keyed “warbling” note produced 
by a multivibrator and thyratron. The report in- 
cludes results of tests, operating instructions, and 
recommendations for an improved model. 

(June 19, 1942) 

285-2 (C-26). Brief description and performance 
characteristics of NLS-518 interference generator, 
the model described in 285-1. 

(February 17, 1942) 


285-3 (C-26) (A. Preisman) . Discusses the ques- 
tion of barrage versus spot jamming with interfer- 
ence generator NLS-518, which is briefly described. 
(June 19, 1942) 


Low-Frequency Dina — Dinamate, 25-105 me. 


Dina 

trans- 

Div. 15 

RRL ' 

Army 

Navy 

mitter 

Dinamate 

re- 

RP-267 

B-3200 

AN/ARQ-8 

AN/ARQ-8 

ceiver 

RP-250 

B-2900-> 




This transceiver transmits a noise spectrum (150 
kc) for spot jamming on the frequency to which 
its receiver is tuned. The operating principles of the 
Dina transmitter are explained in Section 2.2 under 
Dina, 90-220 me. The equipment comprises a 20-w 
suppressed-carrier transmitter (using 884 tube as 
noise source for 150-kc spectrum), a superhetero- 
dyne receiver, and a remote-control box. The trans- 
mitter’s variable-frequency oscillator is the re- 
ceiver’s local oscillator. The circuits are so designed 
that the set may be pretuned to any desired 5-mc 
band in the 25- to 105-mc range and then precisely 
tuned by remote single-dial control of the oscillator 
frequency. With suitable modifications, including 
an added 5 me wide noise source (931 tube) and 
amplifier for the transmitter, the set may also be 
used as a barrage jammer. 

411-TM-20 (H. Kees). Brief description, block 
diagram, and photos. 

411-TM-68 (0. G. Villard, B. Bacorn). Conver- 
sion of equipment for use against German guided 
missiles. 

411-61 (H. Kees, L. Raburn). Field tests with 
installation in B-24 indicated complete jamming of 
15-w amplitude-modulated phone signal at a re- 
ceiver 2 miles from amplitude-modulated trans- 
mitter and 15-20 miles from jammer. 

411-223 (B-4900, RP-344) (W. R. Rambo, G. R. 
Bridgeford) . Gives the results of comparative tests 
on the Radio Research Laboratory [RRL] model 
of B-4100 and a production model of AM-33/ ART, 
an altered version of the prototype. Because the 
prototype was found to be superior in power output 
and bandwidth, various modifications were tested 
for improving AM-33/ART. These are detailed 
in the report by means of performance curves. 
The finally modified unit was thus found to be at 
least the equivalent of the prototype. Equip- 
ment enhances barrage- jamming effectiveness of 
AN/ARQ-8 in frequency range from 26 to 105 me 
with a nominal power rating of 150 w for 4-mc out- 


382 


APPENDIX 


put bandwidth. Two HK257B tubes are used in 
amplifier section and two 836 tubes in the plate 
power section. 

Pad Airborne Transmitter, 21-34 me. 

Div. 15 RP-109 Army AN/ ART-2 

BTL 920-1 1-E Navy AN/ ART-2 

This 50-w barrage jammer is designed for instal- 
lation on single-seater fighter planes for use against 
walkie-talkies. The equipment is essentially a 
superregeneration Dina using a 931 electron multi- 
plier as the source of random noise which is suc- 
cessively amplified by a quenched (blocking) 
oscillator so as to generate noncoherent (random- 
phase) pulses having a duration of about 2 psec 
and a frequency of about 80,000 per second. The 
bandwidth is from 0.25 to 0.5 me. 

940-7 (J. C. Schelleng). Preliminary specifica- 
tions for Pad. 

(October 1, 1943) 

940-11 (A. E. Kerwien). Brief discussion of 
theory, particularly as regards action of self- 
quenched oscillator. 

(January 3, 1944) 

940-16 (W. J. Albersheim, F. F. Merriam) . 
Shows from laboratory measurements and flight 
tests that two Pads will jam Japanese walkie- 
talkies at a much greater distance than will a single 
Pad. The mid-frequencies of the jammers should be 
spaced between 250 and 400 kc. 

(October 2, 1944) 

1179-1. Final report on unsatisfactory produc- 
tion of Pad. 

(December 13, 1944) 

940-1 (RP-199) (R. C. Shaw). Describes an 
early type of 50-w 21- to 43-mc Dina jamming 
transmitter. 

(June 24, 1943) 

940-2 (RP-155) (L. G. Young). Discusses the 
problem of designing an airborne electromechani- 
cal frequency -modulated barrage jammer providing 
a 2-mc band of noise with an output of 300-500 w 
in the 20- to 37-mc range. A proposed method of 
modulation employs a gas-tube source of noise volt- 
ages to actuate a loudspeaker diaphragm. The 
method was found to be experimentally feasible 
except that the diaphragm is liable to large ampli- 
tude vibrations which cause an arcing breakdown. 
Any proposed solution of this difficulty requires 
more complicated alignment and tuning procedures 
than are needed for electronic systems. 

(July 15, 1943) 

940-3 (RP-153) (L. G. Young, G. V. Dale). 


Describes the conversion of an ATR transmitter to 
a barrage jammer employing frequency modulation 
at audio noise rates. Because the transmitter is 
intended merely for training purposes, the 21 -me 
mid-band frequency is not adjustable. The power 
output is 100 to 200 w respectively from maximum 
to minimum, frequency modulation adjustable from 
0 to it 1 me either side of mid-band. The noise 
source is a 2050 gas tube. 

(August 17, 1943) 

940-4 (RP-199) (C. R. Burrows). Discusses the 
theoretical efficiency of spark transmitters used as 
jammers. The basic equipment comprises (1) a 
rotary spark gap with many randomly separated 
spark points to generate noncoherent pulses to mask 
the enemy transmitter, and (2) a band-pass filter 
to distribute the transmitted energy uniformly over 
the desired jamming band. 

(August 24, 1943) 

940-6 (RP-199) (L.E. Hunt). Results of spark 
jammer experiments with type of equipment listed 
in 940-4 indicate that, for a 6-mc bandwidth, out- 
put powers of about 7 w at 60 me and 80 w at 
30 me should be obtainable for barrage jamming. 
Narrow bands might be achieved at a considerable 
sacrifice in power output. 

(September 29, 1943) 

940-9 (RP-199) (A. E. Kerwien). Finds that the 
noise output of 884 gas triode without magnetic 
field falls off as the frequency is increased from 
5 to 30 me. Use of a magnetic field greatly increases 
the noise voltage and causes difficulty with firing. 

(November 3, 1943) 

940-12 (RP-199) (R. J. Kircher, R. W. Friis). 
Describes two laboratory models for a lightweight 
50-w 20- to 40-mc Dina transmitter which were de- 
signed as possible alternatives for the noncoherent 
pulser used in Pad. Both models use an 884 tube as 
the noise source. 

(January 28, 1944) 

940-20 (RP-272) (L. G. Young, N. F. Schlaack, 
F. F. Merriam, R. W. Friis). Tells of the develop- 
ment and performance tests of AM-66/ AR-XR 
power amplifier to be used with AN/ARQ-1 or 
/ARQ-8 for jamming 15- to 55-mc communications. 
The equipment gives a mid-band noise output of 
500 w. 

(February 3, 1945) 

940-21 (RP-132, -150, -152, -153, -155, -199, 
-235, -272, and -356) (M. J. Kelly). Summarizes 
studies and developments of barrage jamming of 
radio communications. The report outlines research 
in frequency-modulated jamming produced elec- 


TRANSMITTERS 


383 


tronically, electromechanically, and by ferromag- 
netic modulation; the use of direct-noise amplifica- 
tion, spark sets, and noncoherent pulses ; and various 
special studies. It tells of the development of 
AN/ART-1, AM-66/AR-XR, and of electrical 
circuits designed for Ground Cigar, as well as of 
the development of expendable jammers. 

(February 20, 1945) 

966-3 (NDRC-15004) (H. H. Benning). De- 
scribes the conversion of Navy GO-9 to a spot 
jammer for the 2.2- to 18-mc range. The 200-w 
output is largely frequency modulation with noise 
over a 10-kc band. The noise may be obtained from 
a microphone in the aircraft engine nacelle or from 
some other external source. 

(March 24, 1943) 

966-10 (RP-148) (V. A. Douglas, W. E. Evans). 
Discusses the conversion of SCR-808 to a jammer 
of communications in 27- to 38.9-mc range. When 
modulated with random noise it gives satisfactory 
performance as a readily tuned spot jammer of a-m 
and f-m receivers. 

(November 23, 1943) 

966-16 (RP-148) (H. H. Benning, W. E. Evans) . 
Describes the conversion of GO-9 for spot jamming 
in the 2.2- to 18-mc range without impairment of 
normal operation for c-w communication. An out- 
put of about 180 w is largely frequency-modulated, 
with a 5-kc or 15-kc band of noise from a 2050 gas 
tube which develops a random noise voltage across 
the oscillator grid-bias resistor. The report includes 
schematic diagram and brief operational instruc- 
tions. 

(September 21, 1943) 

966-27 (RP-358) (W. C. Babcock, R. L. Rob- 
bins, W. H. Tidd, -W. R. Young). Recommends a 
system for spot-jamming German day fighter com- 
munications in order to prevent coordinated attacks 
on bomber formations. An idealized plan for each 
combat wing requires five special planes carrying 
jam and scan equipment. A simplified system using 
fewer sets is proposed as a temporary expedient 
until more sets are available. The report is largely 
concerned with tactical problems. 

(April 27, 1944) 

966-29 (RP-148) (V. L. Dzwonczyk) . Describes 
the conversion of GO -9 for telegraph ROM in the 
300- to 600-kc range provided by the i-f section 
of the transmitter. An output of about 100 w is 
obtained for a 3-kc noise band at any desired fre- 
quency in the range. The added noise source is a 
2051 gas tube placed in the field of a permanent 
magnet. The report includes schematic diagram. 


constructional drawings, brief operational instruc- 
tions, and test data. 

(May 23, 1944) ' 

966-36 (RP-150) (W. J. Albersheim, V. A. 

Douglas, J. W. Emling, W. H. Tidd). Compares 
the effectiveness of airborne barrage jammers of 27- 
to 42-mc communications. Transmitters under study 
included AN/ART-3, the AN/ART-7-9 series, 
AN/ARQ-8, and AN/ART-2. From the standpoint 
of weight, size, and power requirements AN/ART-3 
is found to be the most efficient; it is also the most 
suitable for jamming German tank communications 
and GCI communications. 

(November 10, 1944) 

966-37 (RP-109) (G. J. Heinzelman). Gives 
results of preliminary tests of effectiveness of 
AN/ ARTS high-power Jackal jammer against the 
SCR-608 and SCR-609 f-m links and the German 
a-m tank receiver UkwEe. The report extends and 
corroborates information in 966-32 (Section 3.1). 

(October 12, 1944) 

966-39 (RP-109) (J. L. Lindner, G. J. Heinzel- 
man) . Gives results of influence of microphones on 
jamming effectiveness of Jackal-type noise against 
FuGel6. The tests indicate that with inexperienced 
observers an a-m radio link using throat micro- 
phones for announcing can be more easily jammed 
than the same using conventional carbon lip or 
carbon hand microphones. 

(October 3, 1944) 

966-48 (RP-272B) (M. E. Campbell, C. R. Eck- 
berg, M. C. Francis). Gives results of flight tests 
comparing AM -33 and AM -66 amplifiers with re- 
gard to ease of operation and jamming effectiveness 
against radiophone channels. The AM-66 is found 
to be more quickly tuned and to have an advan- 
tage of 5 db in jamming. 

(March 15, 1945) 

966-50 (RP-272B) (M. C. Francis). Suggests a 
technique for field jamming tests. Flight time may 
be minimized by prior assembly and checking of 
test equipment and prior measurement of radiation 
pattern and resistance of antennas. The results 
obtained under controlled conditions are then used 
to estimate performance on basis of results obtained 
under test conditions. 

(April 20, 1945) 

22 AIRBORNE RADAR JAMMING 
TRANSMITTERS 

“Mandrel,” 85-135 me. 

Div. 15 RP-163 Army AN/APT-3 

RRL B-2000 Navy AN/APT-3 


384 


APPENDIX 


Equipment consists of single transmitter-power 
unit plus remote-control box. The transmitter com- 
prises a master oscillator driving an 829 power 
amplifier whose grid is amplitude-modulated with 
amplified power from 931 noise source. It is rated 
at 10-w output with 2% w in sidebands having 
width of 1 to 2 me, depending on tuning of output 
circuit. For semibarrage jamming the transmitter 
is pretuned before take-off. For spot jamming it 
may be tuned to the desired frequency during flight. 

411-35 (C. W. Oliphant). General description, 
specifications, installation, operation, and main- 
tenance, with photographs and block, circuit, and 
functional diagrams. 

411-TM-19 (E. L. Plotts) . Modifications to cover 
105-155 me. 

411-TM-19A (R. E. Reid, P. P. Robiano). 
Energy spectrum. 

411-15 (L. E. Raburn). Description, specifica- 
tions, assembly of components, wiring diagram, test 
data, and photos of “CXCE,” 85-155 me. 

Div. 15 RP-162 Navy CXCE 

RRL B-1700 

This early type of jammer provided a 15-w c-w 
output optionally a-m or f-m with 100- and 450-mc 
sine waves. It used two HY-75 oscillators with one 
829 power amplifier and an 829 modulator with 
12SJ7 1-f oscillator. As it has been displaced by 
more effective equipment, no further comment is 
needed. 

“Dina,” 90-220 me. 

Div. 15 RP-309 Army AN/ APT-1 

RRL B-2200 Navy AN/APT-1 

Equipment comprises a single transmitter-power 
unit and (optional) remote-control box. The Dina 
(D/rect-Aoise Amplification) transmits a 5-mc 
noise spectrum (20 to 8 w) without carrier and is 
used for either spot or barrage jamming. The trans- 
mitter consists of a local oscillator, a 931 noise 
generator, wide-band preamplifier, mixer, and out- 
put amplifier. The oscillator output is fed to the 
mixer, as is also a selected 5-mc band of amplified 
noise frequencies. They are heterodyned to produce 
two widely separated sidebands whose frequency 
components are equal to the sum and difference of 
the oscillator frequency and the original noise fre- 
quencies. The output amplifier is tuned to either the 
upper or lower sideband to provide a 5-mc band of 
noise at the desired output frequency. For barrage 
jamming the transmitter is tuned before take-off. 
For spot jamming it is tuned during flight by aid of 
a search receiver. 


411-135 (D. A. Peterson) . Reissue of TR-46. 

411-135A. See “Rug,” 220-550 me, in this sec- 
tion. 

411-TM-59 (R. P. Rabbiano, R. E. Reid). 
Energy spectrum. 

411-TM-llO (L. A. Mayberry). Brief descrip- 
tion, explanation of operating principles with block 
diagram, statement on operation and performance, 
and specifications. 

411-TM-16 (J. R. Caraway). Preliminary speci- 
fications and photos of radio-frequency power am- 
plifier, 85-150 me. 

Div. 15 RP-218 Army AM-14/ APT 

RRL B-2800 Navy AM-14/APT 

Tunable wide-band amplifier for B-2200 or 
B-2000 in frequency range from 85-150 me. Its 
power output is from 115 to 140 w with 3-mc band- 
width for B-2200 or 1.5-mc bandwidth for B-2000. 
HK257B beam power tubes are used to eliminate 
need for neutralization as amplifier is tuned over 
frequency range. 

411-TM-48 (J. B. Caraway). Tentative speci- 
fications of radio-frequency power amplifier, 140- 
210 me. 

Div. 15 RP-329 Army AM-18/ APT 

RRL B-3400 Navy AM-18/APT 

Tunable wide-band amplifier for B-2200 in fre- 
quency range from 140 to 210 me, rated at 50-w 
output for 5-mc bandwidth. Eimac 35 TG tubes 
are used in amplifier section. 

“Rug,” 220-550 me. 

Div. 15 RP-164 Army AN/APQ-2A 

RRL F-1500 Navy AN/APQ-2 

Equipment comprises a transmitter unit and a 
power unit. The transmitter employs a tuned oscil- 
lator which is amplitude-modulated with noise from 
the amplified output of a 931 tube. Tuning is done 
by varying the position of shorting bars on the 
grid and plate lines. The power output varies be- 
tween 20 and 5 w as the frequency is increased, 
with from 5 to 1.25 w in the 7-mc sidebands. For 
barrage jamming the transmitter is pretuned before 
take-off and for spot-jamming the pretuned set can 
be accurately tuned over a fairly large band during 
flight by aid of a search receiver. 

411-135 (Z-3700). Comparison of the jamming 
effectiveness of APQ~2 and APT-1 plus AM -18 at 
206 me against SCR-268 at Cambridge, Massachu- 
setts, indicated that the Dina-Amplifier combina- 
tion is about 9 db more effective than the Rug as a 
spot jammer and slightly more effective than the 
Rug as a 4-mc barrage jammer. 


TRANSMITTERS 


385 


411-135A (W-400) (J. F. Youngblood, R. E. 
Anderson). Comparison of the jamming effective- 
ness of APQ-2 and APT-1 (with and without 
AM-18) at 210 me against SCR-588 at Florosa 
Field indicated that, for spot jamming. Rug is 
slightly more effective than Dina alone and 9-10 db 
less effective than Dina plus AM- 18. Rug can be 
tuned more quickly than the Dina combination 
when the antenna load is well matched and low in 
reactance, and less quickly when the load is high 
in reactance. For 4-mc barrage jamming, AM-18 
is 8-17 db more effective than Rug. 

411-206 (E. A. Yunker). Describes a simple field 
modification for operating Rug in the 180- to 
200-mc range with an output of 20 w or more. Any 
10 me in this range may be covered with practically 
no loss in power output by tuning only the plate 
line. The materials needed to make the change are 
2 ft of #14 copper wire and 7 in. of 3/16-in. brass 
or copper rod. 

411-254 (J. L. Clark). Describes a field modi- 
fication permitting operation of AN/APQ-2 in the 
range from 147 to 168 me. This change differs from 
that described in 411-206 chiefly in the addition of 
a loading coil in the antenna pickup loop circuit. 

“Carpet I,” 450-720 me. 

Div. 15 RP-165 Army APT-2 

RRL F-902 Navy APT-2 

Equipment resembles F-1500 except as to fre- 
quency range and addition of small remote-control 
box. Output varies between 8 and 4 w as frequency 
increases, with about ^ total power in 7-mc side- 
bands. Operational procedure is same as for F-1500. 

411-TM-ll (W. D. White). Preliminary speci- 
fications. 

411-TM-14 (John N. Dyer). Methods for select- 
ing and setting frequency. 

411-TM-89 (E. F. Vidro, D. A. Peterson). Pre- 
liminary field test report on performance as spot 
j ammer. 

411-45 (E. A. Yunker). Detailed description, 
photos, block and circuit diagrams. 

411-117 (E. Barrett). Instructions for modifica- 
tions (addition of four condensers between ground 
and the dead ends of the grid and plate lines) to 
improve performance between 480 and 630 me. 
The change eliminates frequency jumps, increases 
power output, and provides more stable operation. 
It also provides less critical adjustment for the 
various oscillator controls, permitting single-dial 
tuning for spot jamming. 

411-150 (E. Barrett, A. Ellis). Specific instruc- 


tions for single-dial tuning of modified (see 411- 
117) Carpet I in the 450- to 650-me range and 
general instructions for any 60-mc range. The total 
frequency range is covered in three bands. For each 
band the antenna coupling control is adjusted for 
best operation at the highest frequency of the band, 
and the antenna tuning stub at the lowest frequency, 
when the transmitter may be tuned solely by plate 
control. 

411-151 (J. F. Youngblood). Reissue of TR-48 
with an added tabulation of the frequency alloca- 
tions relative to the radar frequency for the six 
Carpets. 

“Carpet III,” 475-585 me. 

Div. 15 RP-166 Army AN/APQ-9 

RRL F-2500 Navy AN/APQ-9 

Equipment is a later development than F-902 for 
covering a small part of the frequency range with 
greater power (at least 25 w at 475 me and 15 w at 
585 me). The self-excited oscillator uses two 8012 
tubes in push-pull plate circuit amplitude-modu- 
lated with amplified output of 931 tube. The trans- 
mitter is tuned by means of a front-panel crank 
which changes the size of a pair of parallel plates 
in the anode-grid line, thus varying the character- 
istic impedance. Tuned cathode lines are ganged to 
the same control. An antenna coupling loop and a 
coaxial antenna tuner (to minimize reactance) are 
adjustable by panel knobs. The sideband power is 
approximately 1 w per megacycle for a 7-mc band- 
width. 

411-TM-ll (W. D. AVhite). Preliminary speci- 
fications. 

411-TM-14 (John N. Dyer) . Methods for select- 
ing and setting frequency. 

411-TM-96 (R. B. Monroe, R. R. Rhiger) . Dupli- 
cate of TR-4. 

411-62 (J. L. Clark). Detailed description, with 
block and circuit diagrams. 

411-151. Flight tests of the barrage suitability 
of Carpet III, with and without CHA-28- (3) Win- 
dow dropped at the rate of 60 units per alternating 
current per minute, indicated that a 2-mc barrage 
without Window will shield a tight formation of 
12 heavy bombers and that a 2i/^-mc barrage will 
shield a loose formation of the same number. Used 
as a spot jammer, the Carpet III will shield a tight 
bay of at least 18 heavy bombers, except in the 
overhead position. The foregoing comments regard- 
ing the use of Window with Carpet I also apply to 
Carpet III. 


386 


APPENDIX 


“Air Broadloom III/’ 150-775 me. 

Div. 15 'RP-338 Army AN/APT-4 

RRL F-3400 Navy AN/APT-4 

This 200-w barrage jammer covers its frequency 
range by means of two quickly interchangeable 
split-anode magnetrons, ZP950 (150-390 me) and 
ZP579 (350-775 me), with a single 1,500-gauss 
permanent magnet. The equipment comprises an 
oscillator and cooling unit, a high-voltage supply 
unit, and a modulator and low- voltage supply unit. 
Frequency is controlled by a single dial which 
varies the length of a pair of tuning lines and which 
has a tuning accuracy within dz 3 per cent. Wide- 
band (5-6 me) noise modulation is supplied by the 
amplified output of a 931 tube. 

411-TM-114. Salient facts with block diagram, 
oscillator-modulator circuit, and photographs. 

411-108 (W. D. White) . From the results of jam- 
ming tests conducted against a simulated Wurz- 
burg, it is concluded that the effectiveness of three 
AN/ APT-4 transmitters in covering a 50-mc bar- 
rage is equal to or better than that of fifty 
AN/APT-2 transmitters. Wide bandwidths were 
obtained by overcoupling the transmitter consider- 
ably beyond the point of maximum output. The 
report includes graphs of spectral distribution for 
APT-4 at various central frequencies and graphs 
of relative pulse amplitude for the two transmitters. 

411-139 (L. E. Raburn, G. R. Bridgeford). From 
experiments on the performance of AN/APT-4 it 
is concluded that the single-dial operation is pos- 
sible with a power loss of less than 3 db for the 160- 
to 320-mc range with an AS-114 stub and optimum 
coupling at 250 me, and for the 400- to 775-mc 
range with an AS-115 cone and optimum coupling 
at 550 me. Tuning is accomplished by means of the 
“frequency” control which adjusts the length of the 
resonant lines. Single-dial spot jamming over a 
100-mc range is possible with a loss not much 
greater than 1 db. 

411-204 (W-700, RP-338) (D. F. Wartzok). 
Describes flight tests to determine the jamming 
effectiveness of AN/APT-4 with AS-115APT and 
AS-69APT antennas against a small Wurzburg and 
a synthetic Giant Wurzburg. From the results of 
the tests it is estimated that one APT-4 tuned on 
the radar frequency with optimum coupling and 
with AS-69APT antenna should shield a composite 
echo of 50 B-17’s at 10,000 ft to within 1 mile from 
the small Wurzburg or shield 20 to within 1 mile 
from the Giant Wurzburg. 

411-204A (W-700, RP-338) (D. F. Wartzok). 
Describes flight tests to determine the ratio of the 


jamming power of one APT-4 to the echo power 
from one B-17. This ratio, under certain assumed 
conditions, represents the number of B-17’s that the 
jammer will shield against the radar. The tests were 
conducted against the SCR-545A. They indicated 
that one APT-4, tuned to the radar frequency with 
normal coupling and using a modified AN-148-A 
antenna, will shield 20 B-17’s to a 2y2-im\e range 
from the radar site at an altitude of 10,000 ft. 
Under the same conditions, except for the use of 
AS-41/APT antenna, only four B-17’s would be 
shielded. 

“Carpet IV,” 350-1,400 me. 

Div. 15 RP-336 Army AN/ APT-5 

RRL F-3500 Navy AN/ APT-5 

This 5- to 25-w spot or semibarrage jammer em- 
ploys a lighthouse-type triode oscillator which may 
be tuned from 350 to 1,400 me in any one of three 
300- to 400-mc ranges whose selection requires re- 
moval of dust cover. The main tuning control varies 
the length of a pair of coaxial lines in the cathode- 
grid and grid-plate circuits, and is supplemented by 
a trimmer adjustment and oscillator bias control. 
Dial calibration accuracy is within ± 5 per cent. 
The noise modulator is of standard type with photo- 
electric electron multiplier tube as the noise source 
followed by a wide-band amplifier to provide a 
2-mc bandwidth at any point in the frequency 
range. 

411-TM-120. Brief description, block diagram, 
tube complement. 

411-38. Results of experiments with early models 
of GE L-3 triode as a continuous-wave oscillator in 
coaxial line tuned circuits. (See Section 3.2.) 

411-142 (H. C. Kriegel). Instructions for modi- 
fying F-3500 to increase power output by nearly 
20 per cent in the 350- to 700-mc range with slightly 
greater bandwidth. The change involves using elec- 
tric feedback solely instead of a combined electric 
and magnetic feedback. 

411-196 (W-300, RP-336) (J. F. Youngblood). 
Describes flight tests of the maximum barrage 
spacing of AN/APT-5, unmodified and modified in 
accordance with 411-142, sufficient to screen bomber 
formations from a small Wurzburg. For formations 
of 7 heavy bombers at 12,000 ft and of 14 at 20,000 
ft in to 75-degree elevation, 2 me was found to be 
the maximum spacing for the unmodified equip- 
ment and 3 me for the modified. Further tests indi- 
cated that under certain conditions a barrage plus 
Window combination is less effective than the bar- 
rage alone. 


TRANSMITTERS 


387 


411-TS-7. Tentative specifications of carpet 
sweeper automatic searching jammer, 480-580 me. 

Div. 15 RP-167 Army AN/APQ-1 

RRL r-1800 Navy AN/APQ-1 

This airborne transceiver automatically finds a 
radar signal, locks itself to the frequency thereof, 
and transmits a jamming signal for a predetermined 
time interval. Thereafter it either (1) determines 
whether the signal is still on and, if so, repeats its 
cycle of operation until the signal disappears, or 
(2) proceeds to select and jam another signal. The 
type of operation is preselected by a manual switch. 
As a receiver, it is tuned by a motor-driven revolv- 
ing condenser which sweeps through a selected 
40-mc band until a signal is detected. The amplified 
signal voltage discharges a gas tube in a trigger 
circuit which releases a magnetic latch and actuates 
a relay to connect (lock) the tubes into the trans- 
mitter circuit thus tuned approximately to the fre- 
quency of the received signal. While the set is 
operating as a transmitter, a type 931 tube is ener- 
gized as a noise source from which the oscillator is 
modulated to produce the jamming signal. Jamming 
continues until timing cams close relay contacts 
through which the gas tube is deionized so that 
the set can again operate as a receiver. 
Frequency-Modulated Spot Jammer, 38-50 me, and 
350-1,000 me. 

Div. 15 RP-203 
RRL A-3500 

An experimental 1-f equipment supplies a mini- 
mum of 60-w useful output modulated either by 
random noise (100-30,000 c) or by a sawtooth volt- 
age (900-1,100 c, 1,400-1,600 c, or 2,000-4,000 c) 
to provide a 150-kc frequency-modulation band- 
width at 38 me or a 250-kc bandwidth at 50 me 
(adjustable by panel control). In the oscillator 
circuit there is a type 829 double beam tetrode 
push-pull oscillator modulated by a pair of 6C4 
reactance tubes, the modulating voltage being the 
amplified output of an 884, operated either as a 
noise source or as a sawtooth generator. 

411-TM-40 (W. R. Rambo). Explains theory of 
common-grid type of reactance tube circuit at very 
high frequency, gives mathematical analysis of 
Class A operation, and briefly comments on Class B 
and Class C operation. 

411-TM-40A (J. W. Kearney, W. R. Rambo). 
Indicates behavior of reactance tube circuit at 
ultrahigh frequency, discusses design of 10-w, 350- 
to 1,000-mc circuit using type 2C44 lighthouse 
triode as oscillator with plate and cathode circuits 
tuned by short-circuited sections of transmission 
line, and 2C44 triode as reactance tube. The two 


tubes are installed side by side with grounded grids 
in a common plane and plates tightly coupled in a 
common cavity. The pha^e-splitting network ca- 
pacitance consists of the plate-cathode inter- 
electrode capacitance of the reactance tube, aug- 
mented by electrostatic feedback when necessary. 
The report includes a circuit diagram, curve of 
static modulation, and spectrum of energy distribu- 
tion over a 5-mc band at 775 me wdth highly clipped 
random noise. Parasitic amplitude modulation is 
kept less than 10 per cent with 1 per cent frequency- 
modulation bandwidth. 

411-82 (W. R. Rambo) . Describes Class C opera- 
tion of reactance tubes, analyzes their use in modu- 
lating a 10-w 30-mc oscillator over a 3-mc band, 
and compares results with measurements from an 
experimental model. 

411-TM-76 (W. R. Rambo). Discusses design of 
60-w, 38- to 50-mc model, with circuit diagrams, 
photos, and curve of frequency shift versus grid 
voltage. 

411-TM-90 (J. W. Kearney). Describes a novel 
method of producing wide-band frequency modula- 
tion by using an electron tube to rapidly switch an 
additional inductive reactance into the oscillator 
tank circuit during a fraction of the r-f cycle. The 
resulting shift in frequency is found to depend upon 
the length of the switching period and the size of 
the inductance. The period is the time during which 
the switching voltage exceeds a certain set value, as 
determined by the r-f and modulating voltages. The 
inductance is simulated by transmission lines of 
proper electrical length. Experimental circuits using 
a 2C22 or 6C4 switching tube and the same type of 
oscillator tube with random noise modulation gave 
5- to 6-mc bandwidths at 55 me. Using type 368A 
and 368AS switching and oscillator tubes gave a 
6.5-mc bandwidth at 575 me. The report includes 
circuit diagrams and performance curves. 

Tunable Magnetron Transmitter, 2,700-3,300 me. 

Div. 15 RP-424 Army AN/APT-10 

RRL F-5100 Navy AN/APT-10 

This 50-w jammer is designed for use with a 
modified AN/APR-5 receiver for searching and 
monitoring, a D-2200 panoramic analyzer to aid 
in setting the transmitter to the correct frequency, 
and accessory equipment to provide a complete 
spot-jamming system. The transmitter covers the 
frequency range by means of four interchangeable 
single-dial oscillator plug-in units using four dif- 
ferent magnetrons to cover the entire frequency 
range. The noise source is a 6D4 gas tube giving a 


388 


APPENDIX 


frequency response from 100 kc to 3.5 me. Tuning 
is accomplished by mechanically changing the reso- 
nance characteristics of the magnetron’s internal 
cavity. A line stretcher is also provided in the 
antenna line to prevent “moding.” The antenna sys- 
tem includes one M-4902 with crystal probe and 
two AS/125 antennas. 

411-187 (W-1600, RP-454) (J. M. Moran). De- 
scribes flight tests in three B-17 installations of 
AN/APQ-20, consisting of AN/ APT- 10 trans- 
mitter, AN/APR-5A receiver with panoramic pres- 
entation, and associated equipment. The operator, 
after setting the jammer on the frequency of a radar 
which he has located, simultaneously monitors the 
radar and jamming signals by means of a look- 
through arrangement. Jamming APG-1 was found 
to provide adequate screening above 8,000 ft and a 
look-through range of 3-4 miles, whereas screening 
against SCR-545 was found to be adequate above 
25,000 ft, with a look-through range of 10 miles. 

411-187A (W-1600, RP-454) (J. M. Moran). 
Describes two preliminary flight tests of AN/APQ- 
20 system installed in a B-29. Screening against 
APG-1 was found to be adequate when approach- 
ing at 8,000 ft or higher, and inadequate after pass- 
ing overhead at 15,000 ft or less; the look-through 
range was about 6 miles at 15,000 ft. The system 
is inadequate against SCR-545 below 25,000 ft; the 
look-through range is greater than 25 miles at 
25,000 ft. 

411-265 (W. D. White, J. L. Clark). Briefly de- 
scribes the AN/APQ-20 spot-jamming system con- 
sisting of the F-5100 transmitter, AN/APR-10 
receiver, D-2200 panoramic adaptor, and antennas 
M-4902 and M-6807. 

IB-76. Description and instructions for installa- 
tion, operation, and maintenance of F-4800 trans- 
mitters. 

411-296 (W. R. Rambo). Describes the design 
installation and operation of an interim prototype 
of AN/APQ-21 and discusses receiver and antenna 
requirements for an ultimate system. This noise 
amplitude-modulated transmitter employs a single 
lighthouse ZP-572 (2C38) tube as oscillator and a 
6D4 noise source. It has an output of 10-35 w and 
an average bandwidth of 2 me. By adjusting three 
panel controls, the oscillator frequency may be 
varied from 1,000 me to 1,925 me or from 1,700 me 
to 2,500 me; changing from one range to the other 
requires slight changes in the oscillator. The 300- 
to 1,000-mc range is covered by means of an 1-f 
feedback assembly. The transmitter may be used 
with M-2101 antenna. 


411-266 (W. D. White, J. L. Clark). Describes 
the AN/APQ-27 remote-controlled spot- jamming 
system consisting of the F-5150 transmitter, 
AN/APR-10 receiver, D-2200 panoramic adaptor, 
and antennas M-6807 and M-4902. The frequency 
band is covered by means of six plug-in tuners, 
motor-driven and controlled from a box at the 
operator’s position. The magnetron oscillator should 
be installed near the antenna. A 6D4 tube is the 
source of a 3-mc noise band from a modulator- 
power supply unit installed at any relatively acces- 
sible location. In the control box is a power input 
switch, plate voltage pushbuttons, tuning switch, 
meter for antenna indication, and selsyn frequency 
indicator from the tuning mechanism. 

411-295 (J. G. Stephenson, M. B. Adams). De- 
scribes preliminary experimental work on single- 
dial jammer, 60-300 me. 

Div. 15 RP-346 
RRL F-6300 

This proposed 20- to 50-w spot j ammer with push- 
pull oscillator circuit has single-dial tuning that is 
accomplished by aid of a spiral construction of the 
tank inductance. Maximum output bandwidth is 
obtained by using a small shunt capacitance in the 
tank circuit, simultaneous grid modulation, and a 
balun type of output coupler. Type 3C24 tubes 
are used in the oscillator and a 6D4 is the noise 
source. 

411-TMR-112. Brief description, specifications, 
photos of experimental model, parts list, and con- 
struction drawings. 

411-TM-129 (H. E. Overacker). Brief descrip- 
tion, block and circuit diagrams, specifications and 
details of operating procedure of “Automat” search 
and lock-on jamming system, 40-1,000 me. 

Div. 15 RP-380 Army AN/APA-27 

RRL U-600 Navy AN/APA-27 

This control device automatically sets a jammer 
on the frequency to which a standard search re- 
ceiver (30 me intermediate frequency with single- 
dial tuning) is tuned. It sweeps the receiver over a 
selected frequency range, stops the receiver when a 
signal is received, sweeps a standard jamming trans- 
mitter over the same frequency range, and stops 
sweeping the jammer when it is tuned to the re- 
ceiver frequency. The device provides for all re- 
quired types of search and lock-on jamming. The 
Automat circuits are operated by intermediate fre- 
quency taken from the receiver Panoramoscope 
output plug. The intermediate frequency is fed 
through a high-pass filter into a converter tube 
where it beats with the output of a 30-mc oscillator 


TRANSMITTERS 


389 


to provide video frequencies. These are amplified, 
fed to a sharpening circuit, and applied to a trigger 
circuit whose rectified output operates relays con- 
nected to small motor-drive units attached to the 
front panels of the receiver and transmitter. The 
receiver and transmitter are fed by separate an- 
tennas, that to the receiver being disconnected when 
the jammer is on, receiver pickup then being accom- 
plished through a small separate antenna. 

653-1 (127, RP-136) (P. C. Goldmark). De- 
scribes the development of Pimpernel automatic 
jamming system for the 450- to 590-mc range. This 
airborne equipment consists of a receiver, which 
automatically sweeps any 20- to 50-mc manually 
selected band in the frequency range, and means 
for controlling any associated jamming transmitter. 
Receipt of a radar signal stops the receiver sweep 
at the signal’s frequency, starts the jammer, and 
tunes it to that frequency, and either continues 
interrupted jamming at adjustable intervals or 
ceases jamming and starts new search, as deter- 
mined by panel switch. The report contains photos 
and constructional drawings of model. 

(June 2, 1943) 

1045-3 (BB700, RP-165) (J. T. Wilner). De- 
scribes modifications of Carpet I permitting 335- to 
41 5 -me operation, using the existing RC-156-A 
antenna. The principal changes involve adding con- 
densers to change the resonant frequency of the 
oscillator plate and grid circuits, extending the 
antenna tuning head, and substituting a new pickup 
loop. 

(January 20, 1944) 

2 3 GROUND-BASED AND SHIP-BORNE 
COMMUNICATIONS JAMMING 
TRANSMITTERS 

Cigar 15-Kw Jammer, 38-52 me. 

Div. 15 RP-356 Army AN/MRT-1 

West 1309, 1310 Navy AN/MRT-1 

This readily transportable equipment is carried 
in two HO-27 shelters for the oscillator and power- 
supply units. The oscillator is a self-excited 
WL889R tube with tunable grid and cathode 
Lecher lines. Mechanical noise modulation having 
a 3.5-mc frequency range at 38 me and 7-mc range 
at 54 me is developed by an inductor loop rotated 
between the grid lines. Power is supplied from a 
three-phase source by means of a transformer and 
six-phase mercury-vapor rectifier. The antenna is a 
three-mast, vertical rhombic. 


1309 and 1310-1 (J. T. Thwaites). Brief illus- 
trated description of 38- ^to 52-mc equipment and 
18- to 70-mc modification for countermeasures 
against guided missiles. 

(April 14, 1945) 

1107-1 and 1107-2 (RP-197) (R. M. Baker, 
B. Cassen, and D. Bartlett) . Describe the develop- 
ment, construction, and installation of two special 
resonant-line type f-m oscillators for the Cigar 
project. 

(April 10, 1944 and June 11, 1944) 

940-17 (RP-356) (J. P. Schafer, L. E. Hunt). 
Describes the construction and installation of a 
three-section low-pass filter for suppressing Cigar 
harmonics in the 100- to 150-mc band. Tests indi- 
cate a 64-mc cutoff and a reduction of at least 35 db 
for the unwanted band. 

(October 16, 1944) 

940-18 (RP-356) (P. J. Schafer). Illustrates and 
describes a circuit providing a-f grid modulation of 
Cigar 15-kw output for 100- to 15,000-c operation, 
with no circuit adjustment other than the change of 
input frequency. 

(October 16, 1944) 

940-19 (RP-356) (J. P. Schafer, L. E. Hunt, 
G. V. Dale) . Reports results of investigating means 
for modulating Cigar with random noise. Tests of a 
self -blocking superregenerative circuit controlled 
by circuit noise indicate a smaller power output 
than could be obtained from a system employing 
grid-bias modulation. The latter method was 
adopted and developed to provide a 500-kc noise 
band at 40 me with 12-kw output. Noise from a 
6D4 gas tube amplified by five stages was the 
source of modulations. Investigations were not 
carried beyond the exploratory stage because of 
lack of interest in improving Cigar’s jamming effec- 
tiveness. 

(October 17, 1944) 

1045-10 (BC200, BD301, RP-995). Describes a 
proposed modification of Ground Cigar for spot 
jamming the 38.5- to 42.3-mc radio link of the 
German fighter-control system, which is also briefly 
described. The changes require rebuilding this 
600-w barrage jammer so as to provide spot jam- 
ming with noise from a gas tube and increasing the 
height of the antenna by some 300 ft. From test 
results it is concluded that a Britain-based new 
installation would provide a useful jamming signal 
in the Holland-Ruhr region instead of merely along 
the English coast. 

(July 20, 1944) 


390 


APPENDIX 


2-* GROUND-BASED AND SHIP-BORNE 
RADAR JAMMING TRANSMITTERS 

‘‘Tuba,” 480-500 me. 

Div. 15 RP-lOO Army AN/MPQ-1, 

RRL A-500 SC 94.14 

This high-power barrage jammer is installed in 
and operated from nine trucks with two trailers. 
It comprises two 25-kw transmitters each using a 
resnatron tube separately noise-modulated over 
half the frequency range. The corresponding an- 
tennas are rotatable paraboloids horn-fed from a 
wave guide. Power is supplied from three 75-kw 
diesel-electric generators. 

411-TM-7 (W. W. Salisbury). Preliminary speci- 
fications and discussion of possible applications on 
frequencies between 100 and 3,000 me for ground- 
based, ship-borne, and airborne installations, in- 
cluding drawings of Sloan-Marshall resnatron tube 
and block diagrams for various types of installa- 
tion. 

411-88 (W. G. Dow, J. Galt) . Derives an equa- 
tion for computing the radar-to-jammer distances 
at which a high-power ground-based transmitter is 
effective in jamming a German AI radar operating 
in the 470- to 490-mc range. Assumed operating 
conditions include four types of jammer spectra 
and various positions of target with respect to radar 
and jammer. The results of computations are shown 
by a number of curves in wdiich the distance is 
plotted as a function of the difference between the 
frequency to which the receiver is tuned and the 
mid-band frequency spectrum of the j ammer. These 
curves facilitate choice of the most effective type of 
jammer spectrum. General conclusions are that 
jamming is much more effective when the radar is 
pointed toward the jammer, and that the maximum 
distance for effectiveness increases rapidly with de- 
crease in radar-to-target range. 

411-155 (W-800, RP-lOO) (D. A. Peterson). 
Concludes from described measurements on the 
ground and in the air that Tuba’s field intensity 
at 25,000-ft altitude is sufficient to jam completely 
the German Fuge 202 radar, head on, at a distance 
of 200 miles and including a 32-degree arc. At 
518 me the horizontal beamwidth is 32 degrees 
(110-mile arc 200 miles from Tuba) and the verti- 
cal beamwidth is 5.2 degrees, with the maximum 
lobe directed 3.2 degrees above the horizon. The 
effective jamming range is primarily limited by the 
radar horizon, rather than by the power radiated. 
For one adjustment the bandwidth is about 2 me, 
limiting the equipment to spot jamming. The an- 
tenna has a power gain of 248 over an isotropic 
radiator. 


411-222 (W. Salisbury, E. S. Welch, J. Livin- 
good) . This comprehensive and profusely illustrated 
report presents the technical details involved in the 
successful design, construction, installation, and 
operation of three complete units supplied to the 
British to protect bombers from German night 
fighter radars. Each unit contained two transmitters 
with nominal 25-w rating and actual power output 
depending upon operating conditions and require- 
ments. The transmitters were built around resna- 
tron tube (see 411-70 and 411-126, Section 6.2) 
oscillators. The tubes for the first unit were tunable 
from about 480 to 510 me, for the second unit from 
340 to 520 me, and for the third unit from 460 to 
625 me. Amplitude modulation of the oscillator 
control grid with either noise or sine wave provided 
a jamming bandwidth of 2-4 me, the wider band- 
width being associated with a smaller per cent 
modulation. The first unit functioned effectively 
during the summer of 1944 until the Germans aban- 
doned the 490-mc band. Because of the favorable 
course of World War II the other two units were 
not used against the enemy. Tests indicated they 
would completely jam the Fuge-202 down to 0.2 
mile between the radar and the target when the 
radar is approaching Tuba at an altitude of 25,000 
ft, and at all distances up to 200 miles within a 
32-degree arc. These conclusions assume 14-kw out- 
put within 1 me of the radar frequency. 

Elephant System, 2,000-4,000 me. 

Div. 15 RP-457 

RRL S-9000 

This ship-borne system incorporates 1-kw trans- 
mitting equipment to generate and radiate a noise- 
modulated r-f jamming signal in the 2,460- to 
3,610-mc range and receiving equipment to inter- 
cept enemy radar signals in the 2,000- to 4,000-mc 
range and to present visual information comparing 
the received and transmitted signals. 

Operation of the system is centralized at the re- 
ceiver console housing two receivers, either of which 
may be used with secret antennas, to search for 
enemy radar signals, or with a DF antenna and 
DBM-1 direction finder, to obtain compass bearings 
on the source of a signal. When a search receiver 
intercepts a signal which is to be jammed, the re- 
ceiver is connected to an antenna for monitoring 
the jamming operation. Meanwhile the other re- 
ceiver may continue to search. End receiver uses 
a 2K-48 reflex klystron in a tunable coaxial cavity 
as a local oscillator. Each has a unit for presenting 
the spectrum of a received signal. The output spec- 
trum from the monitor receiver is also switched to a 


TRANSMITTERS 


391 


Panoramic scope in the transmitter console for com- 
parison with the picked-up jamming signal. 

The transmitter uses a ZP-599 magnetron oscil- 
lator modulated with noise from a 6D4 source. A 
transmitting antenna is located at each end of the 
ship. The proper antenna is automatically selected 
and kept trained on a specified bearing by means 
of a system of servo amplifiers operating in con- 
junction with the ship’s gyro on-course system. The 
antenna system includes one for monitoring pur- 
poses and a dummy to absorb power when a jam- 
ming signal is not being transmitted. 

The system was intended to be used with various 
receivers and transmitters so as to cover a wide 
range of frequencies of which only the 2,000- to 
4,000-mc range was actually developed, as detailed 
in the accompanying list of reports. 

411-IB-51. Preliminary instructions for Ele- 
phant. 

411-220 (C-9000, RP-462) (C. C. Loomis). Ex- 
plains the considerations upon which are based the 
design of the radar video analyzer. This is an 
electronic unit which accepts the video output of 
a search receiver and presents it as readings on two 
meters which indicate the pulse width and prf of 
the received signal. The pulse amplitude may vary 
from 0.4 to 2.6 v, the width from 0.5 to 25 fxsec, 
and the repetition rate from 30 to 5,000 c. The unit 
operates on negative pulses from the search re- 
ceiver. The analyzer identifies and reidentifies a 
particular radar indicated by a search receiver, 
assuming that the video characteristics are un- 
changed. 

411-270 (F-9000, RP-461) (W. R. Rambo). De- 
scribes and discusses the salient design features of 
the initial laboratory model for the 90- to 250-mc 
transmitter. Preliminary performance curves indi- 
cate satisfactory power output, modulated band- 
width, and efficiency. 

411-275 (S-9000, RP-457) (J. F. Byrne, J. M. 
Pettit). Final report on RRL development of Ele- 
phant system. 

2 5 EXPENDABLE TRANSMITTERS 

411-59 (G-700) (E. Fubini, T. S. Kuhn). Cal- 
culates the practicability of expendable jammers. 
It is concluded that such an equipment is useful 
in raids against isolated GCI or GL systems whose 
location and frequency are accurately known. The 
weight and volume become too great if these factors 
are not known. The equipment could also be used 


against EW, but is not useful against AI or in 
screening boats, except f^r high-speed boats. 

Dina Chick Jammer 1 to 7 me. 

Div. 15 RP-132 Army SC-95.04 

BTL Navy NS-200 

Ten or more of these parachute devices are 
launched from the bomb racks of moving planes in 
order to jam c-w telegraph and telephone circuits 
within perhaps 1 mile from the place of landing. 
Each unit radiates about 1 w over a specified 500-kc 
band to which it is tuned in the 1- to 7-mc range. 
It operates from dry batteries for about 4 hr after 
a clock-determined starting time. The final model 
employed a 6D4 tube as the noise source with a 
three-stage amplifier and was housed in a cylindri- 
cal container of about the size and shape of a 
100-lb bomb. A 100- to 150-ft trailing wdre was 
used as the antenna. 

940-10 (L. G. Young). Describes an early type 
of 10-w Chick utilizing noise-controlled frequency 
modulation. The method depends upon the varia- 
tion in the inductance of a coil with a Permalloy 
core whose magnetization is varied at random noise 
rates, thus varying the frequency of a two-stage 
oscillator. Development was stopped pending avail- 
ability of 15-lb 90-amp-hr battery to operate six 
tubes, including one 884 noise source. 

(December 9, 1943) 

940-13 (R. C. Shaw, R. W. Friis). Discusses 
various mechanical designs for a unit that will re- 
main in an upright position after landing, thereby 
permitting the use of a self-supporting antenna. 
Complete details are given for a square box type. 

(March 20, 1943) 

940-14 (J. P. Schafer, L. E. Hunt, G. V. Dale, 
L. G. Young) . Recounts the work done in develop- 
ing Dina Chick until concluded pending actual 
Service demand. Details are given with regard to 
mechanical design, antenna and field strength meas- 
urements, and the radio transmitter. 

(April 1, 1944) 

966-7 (NDRC-15004) (V. A. Douglas). Gives 
results of tests of Chick I, an experimental jammer 
consisting of a battery-powered ignition coil and 
spark gap. The device is effective against a-m com- 
munications if the receiver is not overloaded or is 
not equipped with noise-limiting circuits. It has 
little effect on f-m receivers. 

(July 9, 1943) 

966-12 (NDRC-15004) (A. C. Peterson). Dis- 
cusses the oytirnmn size of Chicks and concludes 


392 


APPENDIX 


that 1-5 w is best for use over land and 10 w for 
use over water. 

(August 2, 1943) 

966-22 (G. J. Heinzelman) . Analyzes various 
problems in the use of Chicks as regards number, 
design, power, bandwidth, and type of signal best 
suited for various conditions and terrains. The 
treatment includes the development and applica- 
tion of formulas for determining the required weight 
and number per unit area, the optimum power and 
weight of a unit Chick, and the effect of bandwidth 
on the total weight required for barrage jamming. 

(February 5, 1944) 

966-28 (G. J. Heinzelman, J. W. Emling). Gives 
results of tests on Dina and spark types of Chick 
in order to determine the spectra of the r-f inter- 
ference, the efficiency in converting d-c power to r-f 
interference, and the effectiveness of communica- 
tions jamming. (Interference from the spark type 
is due to the discharge from a spark coil of the 
vibrating interrupter type.) Under ideal conditions, 
the results are essentially the same, being generally 
slightly in favor of Dina. 

(June 15, 1944) 


26 CONTROLLED-DEVICE JAMMING 
TRANSMITTERS 

1.5-Kw Airborne Jammer of Guided Missiles, 20-70 

me. 

Div. 15 RP-419a Army ARQ-11 

AIL 919a Navy ARQ-11 

This equipment consists essentially of a 20- to 
70-mc receiver (R-21/ARQ-11) and a self-excited 
transmitting oscillator having an average output of 
about 1,700 w at 20 me and 400 w at 70 me. The 
output is square wave-modulated in the 100- to 
15,000-c range. In operation, the oscillator’s un- 
modulated carrier at low power is tuned to the fre- 
quency of the enemy transmitter by listening to 
their difference frequency; the full power output is 
then keyed at a predetermined audio frequency. 

1305-8. Handbook of instructions for audio oscil- 
lator 0-28/ ARQ-11 to supply audio input signals 
(30-30,000 c) for modulator unit. 

(March 19, 1945) 

1305-14. Handbook of instructions for radio re- 
ceiver R-21/ARQ-11 with five tuning units, each 
covering one of five 10-mc bands between 20 and 
70 me. 

(June 30, 1945) 

1305-15. Handbook of instructions for C-187/ 


ARQ-11 control unit for distributing power and for 
PP- 130/ ARQ-11 rectifier, of which there are three 
identical 1,000-w units. 

(June 30, 1945) 

1305-TM 1. Describes the gear reduction unit 
designed to drive the tuning apparatus in the 
T-102/ARQ-11 equipment. This provides an accu- 
rate vernier dial for heavy loads and has a unique 
means for eliminating backlash. 

(March 27, 1945) 

1305-18 (RP-421, 419a, b) (J. N. Fricker, 0. H. 
Schmitt, H. W. DeWeese, R. R. Yost, C. F. Noyes, 
A. C. Weld). Describes AN /ARQ-11 and AN/ 
SRQ-11, with photos and circuit diagrams of all 
components. AN/SRQ-11 is a ship-borne version of 
AN/ARQ-11. 

(August 31, 1945) 

1305-17 (913, RP-389) (0. H. Schmitt, R. G. 
Madsen, G. D. Sullivan). Describes AN/SRQ-1 
multichannel jammer to be used against guided 
missiles in the 46- to 51 -me band. The equipment 
utilizes eight low-power oscillators, each adjustable 
to any desired frequency in the band, modulated by 
a square wave at four audio frequencies and ampli- 
fied for 10-w broad-band radiation at the frequency 
of the signals to be jammed. The latter are moni- 
tored over the search band and presented on a 
cathode-ray tube for visual comparison and match- 
ing with the locally generated signals. Means are 
also provided for aural matching for precise tuning. 
Timing circuits permit operation of the search 
equipment for 9 psec and then blank the visual and 
aural presentations. The transmitter then operates 
for 90 psec and the cycle is repeated after a 1-psec 
delay to allow the receiver to reach equilibrium 
after the overload imposed by the transmitter. One 
prototype was completed and operated. 

(August 31, 1945) 

MAS Ship-borne Jammer, 41-51 me. (Division 15, 

AIL, RP-395,915). 

This manually tuned spot jammer is intended to 
jam the control signals of the German HS-293 glide 
bomb and the PC-1400-FX armor-piercing bomb. 
The equipment consists essentially of an untuned 
search receiver and a self-excited 150-w trans- 
mitting oscillator whose frequency is tuned to that 
of the enemy transmitter by aid of the search re- 
ceiver. The jamming signal consists of r-f power 
automatically keyed 100, 1,500, 8,000, or 12,000 
times per second, the modulating frequency being 
interrupted at 0.1 -sec intervals. 

1305-3 (R. F. Schulz, D. M. Miller). Describes 
the enemy missiles and the equipment used to jam 


TRANSMITTERS 


393 


their control systems, including brief operating in- 
structions. 

(January 2, 1945) 

1305-5. Instruction handbook giving data on 
operation and maintenance of MAS. 

(February 12, 1945) 

1305-11 (901, RP-359) (R. F. Schulz, E. W. 
Adams). Traces the development of four experi- 
mental models of automatic search jammer ‘‘Broom’’ 
to be worked against enemy transmissions used to 
control guided missiles such as radio-controlled 
glide bombs. The requirement that most of the 
energy in the radiated signal be concentrated within 
a 50-kc band in the 45- to 51-mc range was met. It 
was found, however, that a single Broom could jam 
only one of two or more signals occurring simul- 
taneously in the search band and that additional 
Brooms would jam one another unless all were care- 
fully interlocked by a complex system. 

(April 21, 1945) 

1305-13 (920a, RP-420a) (0. W. Towner, J. W. 
Wright, P. S. Carter). Tells of the conversion of 
50-kw power amplifiers to provide AN/GRQ-1 
jamming equipment against radio-controlled guided 
missiles in the 20- to 60-mc range. The chief modi- 
fications were the addition of a modulation system 
to give a square-wave output signal and the addi- 
tion of a rhombic antenna system. This ground- 
based jammer was later changed to a truck-mounted 
mobile installation. 

(May 31, 1945) 

27 MISCELLANEOUS JAMMING 
TRANSMITTER STUDIES 

411-TM-27 (M. T. Lebenbaum). Suggestions for 
setting various jamming transmitters on frequency. 
Any airborne jammer should be accompanied by a 
suitable monitoring receiver for spot jamming oper- 
ations. Specific directions are given for tuning 
B-2000, B-2200, F-902, and F-1500 on the ground 
and in the air. 

626-1 (NDRC project C-56) (D. K. Gannett). 
Gives results of testing the effect of interference on 
reception of radiotelegraph signals. Complete loss 
of intelligibility occurs when resistance noise (3-kc 
band) is 10 db stronger than desired signal; nar- 
rowing the band has no effect on per cent errors or 
point of complete failure. Interference due to sud- 
den change in frequency of c-w transmission causes 
complete failure when the interfering energy is 2 db 
stronger than the signal energy; narrowing the in- 
terference band increases the required noise level. 

(May 27, 1942) 


626-2 (NDRC project C-56) (D. K. Gannett). 
Discusses the effect of resistance noise on intelligi- 
bility of telegraph signals and speech. Curves are 
given to indicate the relationship between intel- 
ligibility and noise-to-signal ratio in decibels. 

(June 2, 1942) 

626-3 (NDRC project C-56) (D. K. Gannett). 
Gives results of testing the speech-masking effec- 
tiveness of various superposed noises. Resistance 
noise is found to be more effective than speech 
babble, stepped tones, sawtooth scanning, trains of 
impulses, etc., all of which have gaps in their 
spectra through which fragments of speech may be 
heard. Complete data are presented in the form of 
curves and spectrograms showing the degree of 
masking. 

(August 25, 1942) 

626-4 (NDRC project C-56) (D. K. Gannett). 
Finds that the most effective type of jamming in- 
terference has a spectrum which is continuous in 
time and in frequency and which has a minimum of 
interruption for viewing the jammed signal. Appli- 
cation of a-f resistance noise to an f-m transmitter 
provides a suitable signal for jamming all types of 
a-m and f-m speech and telegraph channels; the 
interference bandwidth may be adjusted by chang- 
ing the degree of modulation. 

(September 22, 1942) 

778-1 (NDRC project C-63) (W. C. Babcock). 
Analyzes those types of vertically polarized electric- 
wave propagation which involve direct transmission 
between a transmitter and receiver plus the effect 
of ground waves over moist soil. Results are given 
in the form of curves showing ground-wave field 
intensity versus distance for various frequencies 
and heights. Usefulness of the data is illustrated 
by finding that the relative effectiveness of strong 
ground-based jammers and weak airborne jammers 
depends upon the wavelength of the signal to be 
jammed (airborne equipment is superior at wave- 
lengths of less than 100 m) . 

(October 19, 1942) 

778-3 (NDRC project C-63) (M. E. Campbell). 
Gives preliminary results of a qualitative investi- 
gation of the effectiveness of f-m jamming signals 
against voice and c-w transmission. The conclusions 
are that a simple f-m signal is not effective against 
continuous wave on a broad-band receiver and is 
slightly more effective against voice transmission 
than is a double-sideband a-m signal. 

(April 28, 1943) 

778-4 (NDRC project C-63) (A. C. Peterson). 
Describes a method for solving transmission prob- 
lems associated with the jamming of ground com- 


394 


APPENDIX 


munications from either the ground or the air. The 
method involves knowledge of a few simple factors 
and the use of plotted curves. It is illustrated by a 
couple of practical examples, such as the maximum 
distance or minimum height from w^hich a specified 
installation can be jammed by specified equipment. 

(January 27, 1943) 

778-6 (NDRC project C-63) (A. D. Fowler). 
Mathematically analyzes the energy-frequency out- 
put spectrum of a noise-modulated f-m transmitter 
and suggests means for improving the spectrum in 
order to provide a suitable type of communications 
jamming signal. Suggested means involves use of 
an “erfer” or error function compressor circuit in 
conjunction with a thermal noise source, a system 
of low-pass filters, and a frequency modulator. 

(January 29, 1943) 

778-9 (NDRC project C-63) (K. C. Black). Re- 
views work done in the study of communications 
jamming as reported in 787-1 to 787-8 and outlines 
plans for future studies under projects 15004, 15005, 
and 15006. 

(February 1, 1943) 

895-5 (P. F. Godley). Presents computed curves 
of r-f propagation above the earth’s surface. The 
curves show the variation in field strength at alti- 
tudes between 300 and 40,000 ft for distances of 25, 
50, and 100 miles and for a number of frequencies 
ranging from 0.6 to 600 me. The general character- 
istics of the propagation are discussed and contours 
are drawn to show the location of the first maxi- 
mum. These curves provide a general picture of 
wave propagation from aircraft to ground. 

(September 11, 1943) 

895-8 (RP-263) (W. A. Anderson). Considers 
the problem of monitoring and tracking a victim 
communications signal that is to be jammed. The 
most promising of severaF methods that were in- 
vestigated is an AFC system which adjusts the 
jammer to zero beat with the victim signal. This 
is a servo arrangement utilizing the reversal in 
phase in the output of a difference frequency modu- 
lator which takes place when the two frequencies 
pass through zero beat. (This proposal ultimately 
led to the development of “Stopwatch.”) 

(October 26, 1943) 

895-34 (RP-263) (W. A. Anderson). Discusses 
the design and testing of the Stopwatch alignment 
system for automatically holding a c-w jamming 
signal to within ± 10 c of a received hand-keyed 
telegraph signal frequency in the 1- to 20-mc band. 
The device incorporates the essential components of 
a radio receiver, transmitter, exciter, and a servo- 
mechanism, utilizing a common oscillator to hetero- 


dyne with both victim and jammer frequencies and 
to feed two similar i-f amplifiers. The “sense” of 
any frequency difference between the two signals is 
determined by phase detectors which actuate a 
servomechanism. The spacing periods of the jam- 
mer telegraph transmission provide the look-in 
intervals required to achieve essentially zero beat 
between the victim and jammer frequencies. Com- 
pared with existing jammers, such as random noise 
or some types of modulation, a jammer equipped 
with Stopwatch effects a 100 to 1 saving in power 
requirements. 

(January 18, 1945) 

1428-1 (RP-263a) (E. Ruth). Summarizes con- 
tractor’s efforts to deliver finished model of Stop- 
watch. 

(December 13, 1945) 

1428-2 (RP-263a). Gives preliminary instruc- 
tions for operating and maintaining AN/URQ-1 
combined receiver and transmitter unit for jam- 
ming continuous-wave and modulated continuous- 
wave signals in the 0.95- to 18.1-mc range. 

(December, 1945) 

895-18 (RP-263) (W. A. Anderson). Describes 
the Quado indicator to provide visual comparison 
of two frequencies differing by less than 5 c, such 
as audio tones obtained when a communications 
receiver is tuned to a distant code signal and a local 
jammer. The device consists essentially of a fre- 
quency standard and special type of motor-driven 
neon stroboscope. (Navy tests indicated that the 
device is not suitable for aircraft use because of its 
susceptibility to noise and the frequency instability 
of the receiver beat-note output.) 

(April 4, 1944) 

895-37 (RP-263) (W. A. Anderson). Describes 
the dual Quado indicator consisting of two strobo- 
trons with means for switching between them so 
that beats from the distant and local transmitters 
appear on separate indicators. (The instrument was 
satisfactory for noiseless signals, but not for the 
intended application because of difficulty in adjust- 
ing the beat note under conditions of noise and 
random keying.) 

(January 27, 1945) 

940-8 (RP-235) (W. J. Albersheim). Describes 
and discusses barrage- jamming tests with r-f noise 
obtained by Dina (direct-noise amplification), by 
frequency modulation, and by Pad (noncoherent 
pulses). Tests using speech modulation were con- 
ducted against double-detection and superregenera- 
tive amplitude-modulated receivers and a fre- 
quency-modulated receiver. A few spot tests 
indicated that noise power required to jam telegraph 


ANTIJAMMING 


395 


code is nearly six times higher than speech jamming 
level. Detailed quantitative report of results can be 
approximately summarized by statement that Dina 
seems to be superior to other methods. 

(October 20, 1943) 


ANTIJAMMING 

3 1 COMMUNICATIONS ANTIJAMMING 

411-20 (K-lOO, RP-126) (A. E. Cullom). Labo- 
ratory experiments on vulnerability of Loran navi- 
gational system (1.95 me) to various types of 
jamming. The tests indicate that the J/S ratios 
(peak jam to peak signal) required for effective 
jamming are approximately as follows: Dina, 7.4 
db; noise (2-36 kc) 100 per cent AM, 10 db; noise 
(2-36 kc) FM, (150-kc swing), 14 db; sine wave 
(12 kc) 100 per cent AM, 18-30 db; sine wave 
(6 kc) FM, (75-kc swing), 18-32 db. The general 
conclusion is that Loran is difficult to jam effec- 
tively. The report includes performance curves and 
sketches of scope patterns. 

966-1 (NDRC-15004) (A. C. Peterson). Presents 
generalized radio propagation curves for estimating 
jammer effectiveness at various heights or distances 
or for various radii of area at frequencies varying 
from 0.6 me to 600 me. 

(March 16, 1943) 

966-2 (NDRC-15004) (R. B. Shanck, V. A. 
Douglas). Discusses the effectiveness of various 
methods of jamming radiotelegraph reception. Pre- 
liminary tests lead to the conclusion that con- 
tinuous-wave [c-w] carrier signals can be most 
effectively jammed by c-w signals closely corre- 
sponding to the telegraph signals. Several objections 
to this method cause preference to be given to AM 
of suppressed jamming carrier with resistance noise 
falling within a narrow hand about signal carrier. 

(March 29, 1943) 

966-3 (NDRC project 15004) (H. H. Benning). 
Summarizes aptitude tests of experienced operators 
in reading through various types of signals used to 
jam telegraph communications. Listed in the order 
of their c-w jamming effectiveness, the signals are 
(1) keyed carrier within 2-10 c of the victim’s 
carrier (a completely impractical condition), (2) 
amplitude modulation with noise, carrier sup- 
pressed, (3) r-f noise, (4) amplitude modulation 
with noise, carrier transmitted, (5) frequency mod- 
ulation with noise, (6) r-f impulses at a-f rate, 
(7) stepped tones. 

(August 22, 1943) 


966-6 (NDRC-15004) (A. C. Peterson^. Explains 
a method for the solution of transmission problems 
associated with the jamming of ground communica- 
tions. The method is an extension of that described 
in 778-4 (see Section 2.7). 

(May 22, 1943) 

966-6C (NDRC-15004). Handbook of propaga- 
tion curves for estimating the received field in- 
tensity of ground-wave signals in 200-kc to 600-mc 
range. 

(October, 1944) 

966-9 (NDRC-15004) (V. A. Douglas). Gives 
results of laboratory tests of AN / ARQ-2 (Jackal). 
The general conclusions are that the device is in- 
effective in jamming f-m receivers and a-m re- 
ceivers equipped with noise limiters. 

(August 10, 1943) 

966-11 (NDRC-15004) (H. H. Benning). Dis- 
cusses the comparative vulnerability of a-m and 
f-m communications, concluding that f-m systems, 
especially when crystal-controlled, are easier to jam 
than are a-m systems equipped with limiters. 

(July 28, 1943) 

966-18 (Project 15004) (W. C. Babcock). Con- 
siders the theoretical requirements for effective 
jamming of German GCI ground-to-plane com- 
munications in 38.6- to 42.2-mc range by means of 
equipment carried by 60 bombers. Complete block- 
out on a barrage basis from any point within the 
control area would require 2.1 kw of r-f power per 
bomber, corresponding to about 350 w per channel. 
With 75 w or more per channel, flight directly over 
the GCI provides the greatest jamming coverage. 
The shortest distance over which a bomber forma- 
tion can attain coverage is indicated by the direc- 
tion of the GCI; this distance can be maximized 
by flight along the boundary line of adjacent control 
areas. Spot jamming should be more effective than 
barrage jamming, particularly with low power. 

(October 22, 1943) 

966-20 (Project 15004) (V. A. Douglas). Rec- 
ommends various changes as a result of tests of the 
effectiveness of AN/ARQ-2 equipment. The most 
important changes are the removal of the noise 
modulation on the condenser unit and the use of 
a 500-c rotating condenser sweep instead of the 
short-circuited turn. Test results are presented in 
detail. 

(October 22, 1943) 

966-21 (RP-109) (K. G. Jansky). Concludes 
that certain enemy ‘"seesaw” signals recorded by 
U.S.A. observers are probably radiated from ro- 
tating beacon stations for navigational use by sub- 


396 


APPENDIX 


marines oii airplanes in 300-1,000 determination of 
location by bearings from two stations. 

(November 10, 1943) 

966-24 (RP-109) (H. H. Penning). Finds that 
the AJ effectiveness of vacuum-tube limiters 
(clipper-slicer type) is very slight on random or 
natural noise. 

(December 28, 1943) 

966-25 (RP-109) (V. A. Douglas, E. O. Bernard, 
M. I. Risley) . Gives test curves on effectiveness of 
mechanical f-m jammers against a-m voice links 
(particularly Fu Ge 16, which is described in de- 
tail) in the 38- to 42-mc range. The signal from a 
single sweep-type jammer is found to be less effec- 
tive than that from a noise-modulated jammer but 
can be slightly enhanced by varying the sweep rate. 
Loss of effectiveness due to limiting devices in re- 
ceiver can be partly overcome by barrage from 
several sweep jarhmers covering entire frequency 
band. 

(April 7, 1944) 

966-26 (RP-109) (C. R. England). Gives results 
of studies of a multicarrier homodyne signal for 
jamming c-w telegraphy. The signal is generated 
by automatically keying a multivibrator alternately 
“on” and “off” for prescribed time intervals; the 
squared up output pulses modulate a 4-mc oscil- 
lator. Depending upon the keying rate and the 
percentage of “on” time the device produces a 120- 
to 160-c band spectrum consisting of six to eight 
carriers with a 20-c spacing. The resultant jamming 
signal appears to be about as effective as a band of 
random noise having the same narrow width. 

(May 22, 1944) 

966-30 (RP-109) (V. A. Douglas). Finds the 
jamming effectiveness of AN/ ART-2 against a-m 
nets to be slightly less than that of f-m noise. The 
effectiveness is not lessened by audio limiters nor 
Lamb type noise suppressors. The equipment pro- 
vides about 1.5 w of useful energy in interfering 
with a 10-kc channel. 

(May 9, 1944) 

966-31 (RP-109). Outlines technical considera- 
tions underlying effective jamming and AJ of radio 
communications. The important characteristics of 
telephone and telegraph signals, the hearing sense, 
receivers, and various types of jamming signals are 
discussed. Ground-wave and sky-wave propagation 
are described with respect to transmission to and 
from aircraft. The influence of antenna efficiency, 
bandwidth, and directivity is considered, as are also 
the various factors which must be taken into ac- 
count in determining range. Discussion of AJ 


methods is brief. The report with its many diagrams 
provides an excellent introduction to a study of the 
jamming of radio communications. 

(May 16, 1944) 

966-32 (RP-109) (V. A. Douglas). Reports on 
the vulnerability of f-m communications receivers 
to mechanical f-m barrage jamming. Tests indicate 
that SCR-608, -609, and -808 are more susceptible 
to the blocking oscillator sweep-type jammers than 
to the simple sweep type. Detailed analyses show 
that American f-m systems may be disrupted by 
mechanical f-m jamming of German a-m com- 
munications. 

(August 1, 1944) 

966-33 (RP-109) (R. B. Shanck). Gives results 
of controlled tests of the comparative ability of ex- 
perienced and inexperienced operators in the recep- 
tion of telegraph signals through interference by 
random noise and five-tone Bagpipes. The former 
displayed greater uniformity in ability than did the 
latter. Random noise was less tolerable than Bag- 
pipes. 

(October 18, 1944) 

966-34 (RP-109) (M. C. Francis). Gives results 
of flight tests of the jamming effectiveness of SCR-8 
modulated with random noise. This airborne 25-w 
f-m transmitter operated against a 10-w 10 WSc 
transmitter in a moving truck and a stationary 
UKwEe receiver. Preliminary results indicated 
satisfactory jamming in the 27- to 38.9-mc range. 

(May 20, 1944) 

966-35 (RP-109) (W. A. Getchell, G. J. Heinzel- 
man, J. L. Lindner) . Reports on effects of jittering 
the sweep modulation of mechanical f-m jammers. 
Jittering causes an improvement of about 4 db in 
jamming effectiveness, which is greatly decreased 
by limiters. The effect is practically independent of 
sweep rates varying from 50 to 100 c except at exact 
multiples of 100 c, when the effect is the same as 
that due to non jittered signals. The latter are most 
effective at 100-200 c and 3,000-4,000 c. 

(August 1, 1944) 

966-40 (H. H. Benning). Discusses general con- 
siderations governing RCM against Japanese com- 
munications, particularly as regards choice between 
intercept and jamming and as regards jamming of 
friendly communications. Airborne barrage jam- 
mers appear to be of little use in the 1.20-mc band 
and should be used in the 20- to 100-mc band only 
when friendly communications can be sacrificed. 
Chicks are useful in jamming some fixed point. 

(September 29, 1944) 

966-41 (RP-109) (G. J. Heinzelman, J. L. 


ANTIJAMMING 


397 


Lindner). Gives results of tests of susceptibility of 
Japanese Model 99 type HiS airborne radio set. 
Susceptibility to jamming from random noise or 
stepped tones is found to be about the same as that 
of an American a-m link using a receiver without 
noise limiters. The Japanese set is somewhat more 
susceptible to interference from an unmodulated 
carrier. 

(November 13, 1944) 

966-42 (RP-109) (G. J. Heinzelman, J. L. 

Lindner) . Gives results of testing the jamming sus- 
ceptibility of Japanese No. 775 meteorological re- 
ceiver. Frequency-modulated carrier and frequency- 
modulated random noise are found to be more 
effective than amplitude modulation or amplified 
random noise. 

(December 9, 1944) 

966-44 (RP-148) (R. L. Robbins). Describes a 
simple type of noise generator for “static burst” 
jamming to cause an enemy operator to ask for a 
repeat of a message which has been obscured while 
being copied by radio intelligence. Noise generated 
by the burning of minute contact areas by current 
passing through a cartridge of loose carbon particles 
is used to modulate the output of a transmitter thus 
employed to simulate static. 

(December 21, 1944) 

966-45 (RP-109) (G. J. Heinzelman) . Finds that 
the jamming susceptibility of Japanese 99 Mark IV 
airborne phone set for 44- to 50-mc range is greater 
than that of other tested superheterodyne receivers 
without noise limiters. 

(January 20, 1945) 

966-46 (RP-109) (G. J. Heinzelman) . Finds that 
the jamming susceptibility of Japanese Mark V 
portable receiver for 0.4- to 7-mc range is substan- 
tially the same as that of a conventional a-m super- 
heterodyne excepting for greater susceptibility to 
spark and sweeping carrier interference. 

(February 7, 1945) 

966-49 (RP-109) (G. J. Heinzelman, E. 0. 
Bernard). Finds that the jamming susceptibility of 
Japanese TM 305 Cl mobile receiver for 19.6- to 
30.6-mc range is relatively great for all types of 
interference. 

(February 8, 1945) 

966-56 (RP-109, -115, -132, -148, -149, -150, 
-233, -259, -272B, -326, -358, -410, -422, -440) 
(M. L. Almquist, R. P. Booth). Outlines the gen- 
eral problems encountered in radio communications 
countermeasures and summarizes the investigations 
reported in 966-1 to 966-55. 

993-1 (RP-122) (H. M. Straube). Discusses the 


theory of automatic tuning qf jammers. The discus- 
sion covers automatic frequency alignment by a 
tracking system which is stabilized to provide mini- 
mum drift by a feedback stabilized system and by 
modulated signal operation. 

(August 13, 1943) 

993-2 (RP-122) (E. R. Taylor). Describes pre- 
liminary design for an airborne multiple spot- 
jamming system whereby from one to four 
AN/ARQ-9 may be simultaneously operated in one 
aircraft in order to jam the same number of com- 
munication channels. Facilities are provided for 
narrow-band and broad-band monitoring. To aid in 
observation of enemy signals the transmitters and 
frequency scanners are synchronously controlled. 

(August 23, 1944) 

993-3 (RP-122) (E. R. Taylor) . Discusses prob- 
lems associated with listening through and aligning 
spot jammers on victim frequencies. Detailed con- 
sideration is given to broad-band and narrow-band 
scanning problems as typified by the design and 
performance of the 18- to 80-mc scanning receiver 
in AN/ARQ-9 and the 1.85- to 18.5-mc narrow- 
band receiver in SCR-596-T2. Considerable at- 
tention is given to the choice of methods for 
minimizing spurious responses and to design im- 
provements based upon performance under abnor- 
mally severe conditions. The report includes typical 
circuit diagrams and performance curves. 

(June 8, 1945) 

778-7 (NDRC project C-63) (K. C. Black, 
W. H. Wise) . Considers the vulnerability of various 
pulse communications to resistance noise. It tenta- 
tively concludes that pulse frequency modulation 
is less vulnerable than pulse amplitude or pulse 
width modulation and that pulse communication 
is less susceptible to barrage jamming with noise 
than are the more conventional forms of trans- 
mission. 

(January 30, 1943) 

895-4 (RP-131) (M. G. Crosby). Compares the 
readability of f-m, a-m, and telegraph systems as 
an index of their relative communication efficiencies 
when jammed by random noise, impulse noise, and 
c-w interference. With random noise, the most 
effective form of interference, telegraphy is most 
readable, narrow-band FM second, wide-band FM 
third, and AM fourth in relative readability. Inser- 
tion of an audio limiter in the transmitter input 
improves a-m reception in the presence of random 
and impulse noise but has little effect for other 
systems and types of interference. Removal of the 
f-m limiter at the receiver has little effect with 
random noise, gives greater interference from im- 


398 


APPENDIX 


pulse noise, and, for critical tuning, improves 
reception in the presence of audible c-w interfer- 
ence. Critical tuning of the f-m receiver improves 
readability. 

(August 24, 1943) 

895-6 (RP-131) (M. G. Crosby). Describes the 
circuit of a differentiating and limiting amplifier 
used to raise the apparent volume level of voice 
communication. (See 895-4.) The device clips the 
higher peaks and raises the amplitude of the low- 
level portion of a voice wave. 

(September 30, 1943) 

895-7 (RP-131) (W. H. Bliss). Gives test results 
on the performance characteristics of ARC-1 re- 
ceiver, including frequency bandwidth and noise 
characteristic curves. The noise level is found to be 
high, whence the effective sensitivity is low. The 
lack of single-dial tuning is disadvantageous for 
general signal hunting, since weak signals may be 
missed. 

(October 22, 1943) 

895-19 (RP-131). Instructs on the use of narrow- 
hand f-m adapter for BC-603-D receiver under con- 
ditions of low signal strength, high noise level and 
radio interference. Its 8-kc band is accepted with 
only a slight sacrifice in the quality of speech repro- 
duction. 

(April 26, 1944) 

895-41 (RP-123, -131, -198, -227, -228, -229, 
-230, -231, -252, -260, -263, -325, -345, -352, -420b, 
-460) (H. H. Beverage). Recapitulates jamming 
and AJ techniques investigated under contract 895. 
In addition to these projects for which separate 
reports are given (and digested) , the report includes 
accounts of preliminary studies of (1) expendable 
transmitter “Hen” for propaganda broadcasting, 
(2) an electrical cancellation and indicating system 
for submarine detection and panoramic presenta- 
tion of radio and radar signals, and (3) antenna 
system for ground-based jammer of guided mis- 
siles. 

(October 10, 1945) 

895-14 (RP-123) (J. B. Atwood, G. E. Hansell). 
Discusses jamming and AJ tests of a pulse phase- 
modulation system of voice communication. For a 
receiver whose circuit details are not known the 
most effective jamming signal is found to be an r-f 
spectrum of random noise gated 50 per cent cover- 
ing the receiver’s i-f bandwidth. Phase-modulated 
pulses and c-w jamming were also tested. When the 
receiver is known to have certain circuit arrange- 
ments, savings up to 26 db in jamming power may 
be obtained. The most effective AJ device is a pass 


circuit which is selective as to both the amplitude 
and the slope of the pulse. 

(February 16, 1944) 

895-25 (RP-123) (J. B. Atwood, G. E. Hansell). 
Describes the pulse amplitude selective automatic 
gain control circuit whose pass portion was used in 
the AJ tests discussed in 895-14. The automatic 
gain control circuit maintains the receiver gain at 
the proper level in the presence of strong inter- 
fering pulses. The pass circuit responds to a narrow 
range of pulse amplitudes and does not transmit 
pulses of higher or lower amplitude. The combina- 
tion of the automatic gain control and pass circuit 
provides communication reception which is rela- 
tively free from jamming. 

(July 22, 1944) 

895-26 (RP-123) (J. B. Atwood, G. E. Hansell). 
Describes f-m pulse jamming tests of a pulse phase- 
modulation system of voice communication. Com- 
parison with the results of phase-modulation pulse 
jamming (see 895-14) show definite power savings 
for FM. If the circuit details of the receiver to be 
jammed are not known, an r-f spectrum of random 
noise gated 50 per cent is still the most effective 
j ammer. 

(August 7, 1944) 

895-30 (RP-123) (J. B. Atwood, G. E. Hansell). 
Finds that the effect of noise jamming of a pulse 
frequency -modulation system of voice communica- 
tion is to vary the width of the pulse and thus 
greatly reduce the signal-to-noise ratio. Circuits for 
eliminating the variation in width are shown and 
a formula is derived to give the improvement thus 
obtained in the signal-to-noise ratio. 

(October 25, 1944) 

895-36 (RP-123) (J. B. Atwood, G. E. Hansell). 
Describes two types of short-pulse f-m receivers 
and discusses their susceptibility to various kinds 
of jamming signals. One type of receiver using a 
trigger circuit and low-pass filter for detection is 
easily jammed. In the other type of receiver the 
pulses are converted into sine waves which are 
passed through a double limiter and a discriminator. 
The report concludes the investigations of jamming 
and AJ tests previously reported, making no radical 
change in conclusions. 

(January 23, 1945) 

895-12 (RP-228) (C. N. Gillespie). Evaluates 
the AJ characteristics of a facsimile transmission 
system in which a narrow-band amplitude- 
modulated receiver is used with a wide-band 
frequency-modulated transmitter modulated by a 
black and white signal. The receiver detects a pulse 


ANTIJAMMING 


399 


each time its pass band is swept by the frequency- 
modulated signal, thus recording only the edges or 
transients of the original picture. Studies indicate 
that the consequent loss in detail inherent in the 
“transient system” is not counterbalanced by the 
improved signal-to-noise ratio. The transient sys- 
tem also requires very precise operating adjust- 
ments of background. Existing facsimile type sys- 
tems are thus fully as satisfactory with respect to 
operation under jamming conditions. 

(January 12, 1944) 

895-13 (RP-227) (J. A. Spencer). Discusses 

means for improving the AJ characteristics of 
printing telegraph systems, particularly the five- 
unit start-stop teletype and the seven-unit radio 
printer. The systems are found to be less vulner- 
able to fluctuation noise than to square-wave 
impulses. The most satisfactory AJ circuit arrange- 
ment includes space diversity reception, two-tone 
frequency-modulated keying and seven-unit opera- 
tion employing synchronous transmission with 
front-end correction and collation (transmission 
and reception of each character code combination 
several times). 

(January 15, 1944) 

895-20 (RP-229) (E. R. Shenk, J. A. Spencer, 
E. B. Anderson). Discusses the AJ characteristics 
of Beechnut, a British system of ideograph trans- 
mission for communication between ground and 
aircraft. Tests demonstrate that this system can 
be effectively jammed by: (1) jamming carrier 
having half the amplitude of the desired carrier and 
100 per cent modulated by a superaudio tone whose 
frequency is approximately equal to the frequency 
of the Beechnut transmitted marking tone; (2) un- 
modulated jamming carrier having three-fourths 
the amplitude of the desired carrier and differing 
from it in frequency by the frequency of the mark- 
ing tone. The use of fluctuation noise or barrage 
jamming is found to be relatively ineffective. 

(April 15, 1944) 

895-28 (RP-229) (J. E. Smith, E. R. Shenk, J. R. 
Weiner). Finds that the demodulating effect of a 
strong jamming signal upon a weak desired signal, 
when both are simultaneously present in the input 
of a linear detector, can be largely overcome through 
the use of a capacitor in shunt with the detector 
load resistor. Such a peak detector is most useful 
when the frequency difference of the two carriers 
is three or four times the maximum desired modula- 
tion frequency, a condition which often exists in 
u-h-f receivers. Care must be used in designing the 
first audio coupling network and automatic gain 


control filter circuit when the jamming ;carrier is 
keyed. 

(September 18, 1944) 

895-39 (RP-229) (J. E. Smith, J. A. Spencer, 
E. R. Shenk, L. P. Reinhold). Describes the Voflag 
impulse signaling system of radio communication 
between a base station and a multiplicity of air- 
craft. The system is designed to be less susceptible 
to jamming than is the British “Beechnut” system 
for ground-to-aircraft communication by display- 
ing a six ideogram message before the pilot. The 
Voflag uses two-tone polar telegraph keying with 
an error-proof code having the characteristics of an 
automatic telegraph. Provision is made for both 
manual acknowledgment and automatic answer 
back. An attachment to the airborne portion per- 
mits the recording of a printed message in addition 
to the visual display. 

(October 24, 1945) 

895-38 (RP-460) (B. A. Trevor). Describes the 
apparatus and procedure in determining the jam- 
ming characteristics of AN/TRC-5 pulse communi- 
cation system. The system is found to be relatively 
invulnerable, since effective jamming requires an 
airborne jammer situated within a narrow range of 
angles, thus limiting the jamming time for inferior 
air power. The most effective jamming occurred at 
about a 10-kc pulse rate with 1- or 2-psec pulses. 
The report includes AJ suggestions. 

(May 29, 1945) 

895-42 (SO-26005, RP-460). Finds that photo- 
tube demodulation of time division multichannel 
pulsed signals which are synchronized on a cathode- 
ray tube is not a satisfactory method for identifica- 
tion and analysis with airborne equipment. Tests 
were made with signals from AN/TRC-5 viewed 
on AN/APA-11 and on 715A oscilloscope. Intelli- 
gible modulation requires 'a very bright trace on a 
cathode-ray tube at least 5 in. in diameter and is 
then rather noisy. 

(October 17, 1945) 

936-1 (RP-159) (E. Labin, D. D. Grieg, R. B. 
Reade). Discusses the problems and factors in- 
volved in the jamming and antijamming of radio- 
telegraphy. The discussion covers the results of ex- 
haustive tests of all types of jamming at both audio 
and radio frequencies and also covers AJ studies 
involving the use of protective limiters for tele- 
graph receivers. The conclusion is that limiters are 
effective against noise signals that interfere with 
idealized laboratory receivers. 

(September 10, 1943) 

936-2 (RP-159) (E. Labin, D. D. Grieg, R. B. 


400 


APPENDIX 


Reade). Discusses the results of further studies of 
the jamimng and antijamming of radiotelegraphy. 
The reported results are for jamming tests without 
limiter against Navy RBC-1 and Army BC-342-N 
receivers and for AJ tests of the receivers with pro- 
tective limiter. The significant conclusions are that 
the existing internal limiters of the RBC-1 are in- 
effective against resistance noise jamming, that 
maximum AJ improvement is obtained by placing a 
clipper-type limiter between the last i-f stage and 
first a-f stage of the receiver, and that the improve- 
ment in reception due to the limiter action is 
vitiated by keying the clipped noise jamming signal 
at a code speed rate. 

(April 1, 1944) 

936-3 (RP-159) (E. Labin, D. D. Grieg, R. B. 
Reade). Gives results of jamming telegraphy with 
keyed noise compared with those obtained with un- 
keyed noise. The general conclusion is that any 
effective jamming signal may be keyed on and off 
without reducing its effectiveness, provided that due 
respect is paid to the adjustment of duty cycle and 
keying rate. In other words, the effects of keying 
are independent of the spectrum of the uninter- 
rupted modulated jamming signal. 

(July 25, 1944) 

936- 5 (RP-159) (H. H. Buttner). Summarizes 
the results of experimental jamming and AJ of 
telegraphy. In addition to data from 936-1, -2, -3, 
and -4 (see above and Section 1.4) this report tells 
of assistance given in field tests of Radio Research 
Laboratory [RRL] models and of evaluation tests 
of Navy XGE modulator used as a jammer. 

(April 30, 1945) 

937- 1 (RP-124) (S. H. Dodington). Proposes a 
program for developing a radio communication sys- 
tem protected against interference by jamming 
voice channels in the 2- to 9-mc range. The general 
plan calls for some form of radio printer, several 
types of which are described. 

(February 19, 1943) 

937-2 (RP-124) (E. M. Deloraine). Discusses 
preliminary results obtained in developing a pro- 
tected communication system to withstand jam- 
ming. In place of voice communication, the system 
employs a nine-frequency printer (to obviate need 
for training operators in Morse code under jamming 
conditions) and a two-frequency peak rider circuit 
to eliminate ‘^apparent demodulation.” As the lat- 
ter is only partially effective, development will be 
continued. 

(April 28, 1944) 

937-3 (LD51-301, RP-124) (H. Busignies, S. H. 


Dodington, J. A. Herbst, G. R. Clark) . Describes a 
two-way aircraft radio communication system 
partly protected against interference. Protection is 
afforded by audio filters which select only those fre- 
quencies which are conveying intelligence and reject 
all other components of the audio signal. As the 
method precludes voice communication, a tape 
printer is employed to present a visual message sent 
by means of a keyboard resembling that of a type- 
writer. The printer will operate through noise- 
modulated jamming or atmospheric noise that is 
about 11 db stronger than the desired signal. 

(July 12, 1945) 

1024-1 (RP-189) (S. L. Bailey). Discusses vul- 
nerability of FuGe receiver to Cigar type of jam- 
ming with frequency-modulated signal. It is con- 
cluded that the jamming effect is primarily due to 
listener fatigue and only secondarily to distortion 
of intelligence in the circuits of the receiver. 

(January, 1944) 

1024-2 (RP-189) (R. H. Culver). Recounts the 
development of a reliable gas-tube noise generator 
circuit using a type 2050 tube to produce a 20-kc 
band of noise uniformly. 

(January, 1944) 

1024-3 (RP-189) (D. C. Ports) . Discusses meth- 
ods for decreasing susceptibility of f-m receivers 
to c-w jamming. The most effective method is found 
to be a back-biasing system applied to one stage of 
the i-f amplifier designed with a sharp cutoff. The 
bias should be automatically adjusted to approach 
cutoff in order to eliminate the capture effect and 
yet recover enough of the original speech in the 
distorted output to make it intelligible. 

(March, 1944) 

1024-4 (RP-189) (0. W. B. Reed). Reports the 
results of jamming tests against BC-603-D receiver 
as used in mobile f-m radiophone equipment. It is 
found that this receiver may be jammed by a step 
tone of noise f-m jammer when interference devia- 
tion fills the receiver pass band and has a field 
strength equal to that of the desired signal. An 
improvement of 2-5 db may be obtained by increas- 
ing the deviation of the desired signal. 

1024-5 (RP-189) (F. T. Mitchell, P. F. Hoff- 
mann). Gives results of jamming tests against BC- 
659-B receiver in the SCR-609-A portable trans- 
ceiver. Frequency-modulated jamming with noise 
or stepped tone is found to be most effective against 
this f-m equipment. 

(May, 1944) 

1024-6 (RP-189) (O. W. B. Reed, E. H. Scheibe) . 
Gives results of preliminary jamming tests against 


ANTIJAMMING 


401 


BC-624-A airborne receiver. The noise suppressor 
developed by the American-British Laboratory of 
NDRC Division 15 [ABL-15] now incorporated in 
the receiver is found to be entirely satisfactory. 

(June, 1944) 

1024-7 (RP-189) (0. W. B. Reed, E. W. Scheibe) . 
Gives results of jamming tests against AN /TRC-1 
field teletype equipment used in conjunction with 
Signal Corps four-channel carrier-telephone system. 
The equipment is found to be more or less vulner- 
able to all conventional types of jamming. Defense 
may be afforded by switching to one of the other 
three channels, all of which should always be avail- 
able. 

(June, 1944) 

1024-8 (S. L. Bailey, W. J. Albersheim, M. L. 
Almquist, H. H. Benning, V. A. Douglas, J. W. 
Emling, J. H. Moore) . Suggestions for standardized 
definitions and methods of testing effectiveness of 
communications jamming. They represent practice 
at Bell Telephone Laboratories, Inc., and Jansky & 
Bailey Laboratory. 

(July, 1944) 

1024-9 (RP-189) (P. F. Hoffmann). Gives re- 
sults of jamming tests against BC-IOOO-A receiver 
in SCR-300-A portable transceiver in 40- to 48-mc 
range. It is vulnerable to f-m jamming with noise 
or stepped tunes and to continuous wave. 

(August, 1944) 

1024-10 (RP-189) (0. W. B. Reed, E. H. 
Scheibe). Gives results of jamming tests against 
233A airborne transceiver in 100- to 156-mc range. 
The set is found to be quite vulnerable. 

(October, 1944) 

1024-11 (RP-189) (0. W. B. Reed, E. H. 
Scheibe). Gives results of jamming tests against 
BC-639-A ground receiver in 100- to 156-mc range. 
The receiver compares favorably with other receiv- 
ers in this frequency range. 

(September, 1944) 

1024-12 (RP-189) (0. W. B. Reed, E. H. 
Scheibe) . Gives final results of jamming tests 
against BC-624-AM receiver in 100- to 156-mc 
range. Better performance against pulsed carriers is 
provided by a new noise suppressor. Performance 
against frequency-modulated and continuous-wave 
jamming is not so good. 

(September, 1944) 

1024-13 (RP-189) (0. W. B. Reed, E. H. 
Scheibe). Compares vulnerability of 233A, BC- 
624-AM, and BC-639-A a-m airborne receivers to 
various types of jamming. The general conclusion 
favors the incorporation of noise limiters. 

(October, 1944) 


1024-14 (RP-189) (P. F. Hoffmann). Gives re- 
sults of testing the vulnerability of BC-348-R air- 
borne amplitude-modulated receiver in 0.2- to 
0.5-mc and 1.5- to 18-mc ranges. The receiver is 
most vulnerable to FM by noise or stepped tones of 
low deviations. Pulsed carrier jammers are rela- 
tively ineffective, as is likewise c-w jamming. 

(November, 1944) 

1024-15 (RP-189) (D. C. Ports). Finds that 12- 
to 24-db peak clipping of audio voltages before 
modulating in a communications transmitter im- 
proves the intelligibility of reception through noise- 
modulated f-m jamming. 

(December, 1944) 

1024-16 (RP-189) (E. H. Scheibe) . Gives results 
of jamming tests against BC-343-N and BC-312-N 
ground-based receivers in 1.5- to 18-mc range. They 
are found to be more susceptible when used for 
voice than when used for continuous-wave or modu- 
lated continuous-wave communication. An f-m 
jammer modulated with step tones is most effective 
against voice communication. 

(December, 1944) 

1024-17 (RP-189) (F. T. Mitchell) . Gives results 
of tests of the jamming effectiveness of modified 
step-tone jammer having a peak clipper and five 
tones in the 500- to 700-c range plus a 180-c note 
instead of five tones in the 300- to 600-c range. The 
modification is found to improve the effectiveness 
when the jammer is tuned to zero beat with the 
signal. The a-m jammer, however, is found to be 
less effective than an f-m jammer. 

(January, 1945) 

1024-18 (RP-189) (P. F. Hoffmann). Gives re- 
sults of jamming tests against BC-625-A mobile re- 
ceiver in 2- to 6-mc range. Continuous wave and 
modulated continuous wave are found to be harder 
to jam than voice communication, which is easily 
jammed by FM. 

(January, 1945) 

1024-19 (RP-189) (0. W. B. Reed). Gives re- 
sults of jamming tests against BC-699-C receiver in 
1.68- to 4.45-mc range. The receiver is found to be 
most vulnerable to f-m jammers with step tones or 
noise at low jammer bandwidths. 

(January, 1945) 

1024-20 (RP-189) (0. W. B. Reed). Gives re- 
sults of jamming tests against BC-654-A mobile re- 
ceiver in 3.8- to 5.8-mc range. Susceptibility is much 
the same as that of BC-699-C. 

(January, 1945) 

1024-21 (RP-189) (P. F. Hoffmann). Compares 
vulnerability of BC-348-R, -342-N, -312-N, -652- A. 


402 


APPENDIX 


-669-C, -659-A. In general, BC-348-R is found to be 
superior to the others. 

(February, 1945) 

1024-22 (RP-189) (E. H. Scheibe). Gives the 
operating characteristics of SCR-536 portable press- 
to-talk radiophone in 3.5- to 6-mc range. Perform- 
ance is found to be generally satisfactory. 

(February, 1945) 

1024-23 (RP-189) (E. H. Scheibe). Gives results 
of jamming tests against AN/ ARC-1, original and 
modified to reduce effectiveness of pulsed carrier 
interference. The modification results in improved 
J/S ratios for wide-sweep f-m and pulsed carrier 
jammers. For other types of jamming no improve- 
ment is effected. 

(March, 1945) 

1024-24 (RP-189) (D. C. Ports). Summarizes 
data on the AJ characteristics of f-m communica- 
tions receivers. Pulse-type jamming signals are 
found to be ineffective in reducing intelligibility. 
Severe jamming is caused by FM having a devia- 
tion approximately equal to half the pass band of 
the receiver. An f-m receiver is also rather vulner- 
able to other types of jamming. The report dis- 
cusses design features that contribute toward the 
most efficient AJ operation. 

(March, 1945) 

1024-25 (RP-189) (P. F. Hoffmann). Gives re- 
sults of tests of the vulnerability of ARB aircraft 
receiver in 195- to 9,050-kc range. The receiver is 
found to be susceptible to all the conventional types 
of jamming except pulse jamming at low repetition 
rates. 

(May, 1945) 

1024-26 (RP-189) (0. W. B. Reed). Reports on 
the electrical characteristics and vulnerability of 
SCR-511-B receiver in 2- to 6-mc range. The char- 
acteristics are found to be generally satisfactory. 
The receiver is more susceptible to jamming than 
other ordinary communication gear covering a com- 
parable frequency range. 

(June, 1945) 

1024-27 (RP-189) (P. F. Hoffmann). Discusses 
use of J/S ratio in r-f pulse jamming tests. This 
ratio, expressed in decibels, is that of peak pulse 
jammer power to signal carrier power in the trans- 
mission medium at the receiver. The use of this 
ratio is illustrated in a method for indicating the 
field intensity at the receiving antenna during the 
time that the jamming transmitter is pulsed “on.’’ 
The report also discusses the results of tests show- 
ing the decrease in vulnerability of ARB receiver 
with Goodyear limiter. 

(July, 1945) 


1024-28 (RP-189) (E. H. Scheibe) . Gives results 
of further study of AN / ARC-1 electrical circuits. 
Excessive noise at low signal levels was found to be 
caused by too rapid AVC action on the r-f stage. 
Modifications to reduce it are suggested. 

(August, 1945) 

1024-29 (RP-189) (0. W. B. Reed). Discusses 
the electrical characteristics and vulnerability of 
AN /TRR-2 transportable equipment consisting of 
a radio receiver designed to pass only a definite r-f 
signal having specific a-f modulation and an elec- 
tromechanical switch to detonate a mine when a 
definite sequence of pulses is received from an acti- 
vating transmitter (AN/TRT-1). Tests indicate 
that a simple barrage jammer will prevent the sys- 
tem’s operation, either falsely or when required. 
The extreme vulnerability is found to be due to the 
use of tone selection and impulse keying combined 
with a superregenerative receiver. 

(September, 1945) 

1024-30 (RP-109a) (E. H. Scheibe) . Reports on 
the vulnerability of the Japanese model 96 Mark 
4E transmitter-receiver in 4- to 4.9-mc range. The 
receiver is found to be more susceptible when used 
for voice communication than for continuous wave, 
the most effective jammers being amplitude-modu- 
lated tuned to zero beat with the desired carrier. 

(September, 1945) 

1024-31 (RP-189) (E. H. Scheibe). Gives the 
electrical characteristics of AN/TRC-8 consisting 
of f-m receiver R48/TRC-8 and f-m transmitter 
T30/TRC-8 with power peak. The equipment oper- 
ates in the 230- to 250-mc range, for which equip- 
ment was not available for making vulnerability 
tests. The characteristics are such that it is pre- 
dicted that the receiver cannot discriminate against 
f-m jamming, is susceptible to c-w jamming, and 
has low vulnerability to jamming by pulsed carrier 
interference. 

(September, 1945) 

1024-32 (RP-109a) (P. F. Hoffmann). Gives re- 
sults of preliminary tests of vulnerability of Jap- 
anese Model B mobile transmitter-receiver. The 
equipment is found to be more susceptible to jam- 
ming than are similar units used by U. S. Armed 
Forces. Its performance characteristics are likewise 
inferior, particularly as regards modulation capa- 
bilities. 

(September, 1945) 

1024-33 (RP-189) (S. L. Bailey). Gives results 
obtained in testing vulnerability of AN/SWR-2 
receiver designed for use aboard boats to be re- 
motely controlled by an airborne transmitter. The 


ANTIJAMMING 


403 


equipment is found to be extremely vulnerable to 
c-w jamming, since the control signals are tones 
which are selected by filters in the receiver. The re- 
ceiver is also quite vulnerable to pulses. Simple 
changes are suggested for reducing susceptibility to 
pulse jamming. 

(October, 1945) 

867.6 (RP-318) (M. M. Freundlich). Discusses 
the use of dark-trace tubes for integration in scope 
detection of weak signals. (A dark-trace cathode- 
ray tube provides slow decay of an image on an 
alkali-halide screen.) Experimental results indicate 
a possible slight advantage wRich does not warrant 
discarding conventional tubes before dark-trace 
tubes are improved. 

(December 16, 1943) 

32 RADAR ANTIJAMMING 

411-24 (E-200, RP-171) (0. G. Villard). Labo- 
ratory tests in jamming SCR-268 (Type A presen- 
tation) with continuous wave, pulses, amplitude 
modulation, and noise. Reasons for observed be- 
havior are given, as are also suggestions for AJ 
procedure. The general conclusion is that the gen- 
eral direction and range of the target and jammer 
can usually be determined while the radar is being 
jammed with any of the types of signal under test. 
The report includes photos of scope patterns for 
various values of jamming field strength in micro- 
volts per meter at the radar mount. 

411-36 (E-300, RP-222) (0. G. Villard, S. E. 
Kaisel). Laboratory tests in jamming SCR-521A 
(176-mc ASV radar). The general conclusions are 
that noise provides the most effective jamming sig- 
nal, that jamming effects can be minimized by 
adjusting receiver gain control to provide optimum 
response from the target, and that the pip can often 
be restored by slightly detuning the local oscillator. 
The r-f selectivity and shielding are such that a 
radar system can be jammed only by a signal tuned 
close to its carrier frequency. The report includes 
photos of scope patterns. 

411-53 (E-500, RP-224) (D. R. Scheuch, S. F. 
Kaisel). Laboratory tests in jamming Mark IV 
(700 me). Comments duplicate those for 411-36. 

411-41 (A-1200) (E. W. Schuler, J. J. Livingood, 
J. H. Woodruff). Laboratory experiments in jam- 
ming Type A and plan-position indicator \PPI] 
presentations of ASG-1 (SCR-617) 10-cm radar by 
means of klystron transmitter and 30-in. paraboloid. 
It is concluded that (1) ASG-1 can be jammed so 
as to prevent determination of range but not pre- 


vent determination of direction, (2) one-channel set 
is more vulnerable than two-channel set,' (3) filters 
will reduce effectiveness of' c-w jamming but not of 
short pulse jamming, (4) 10 db less power is re- 
quired for jamming with 100 per cent amplitude 
modulation than with continuous wave, (5) avail- 
able klystrons not powerful enough to jam 360 
degrees of PPI scope. The report includes photos 
of screen images for various types of jamming. 

411-42 (L-400, RP-172) (J. H. Woodruff). Tests 
on susceptibility of ASG (Army SCR-617) to vari- 
ous types of jamming. The general conclusion is 
that this 10-cm airborne radar is satisfactory with 
respect to its ability to operate in the presence of 
enemy jamming. The use of the gain control is an 
effective AJ measure for c-w jamming, and where 
the jamming is very strong it is always possible to 
DF on the jammer. For both noise and sine-wave 
a-m jamming, reduction of receiver gain is useful. 
Noise and sine-wave f-m jamming do not reduce 
the effectiveness of slightly detuning the receiver’s 
local oscillator as an AJ measure. 

411-TM-107 (L-105, RP-385) (W. W. Farley). 
Field tests with L-105 jamming signal generator 
against Mark 8 (fire-control) radar. The L-105 con- 
sists of a 410-R klystron (20-w unmodulated) with 
associated regulators and power supplies. The modu- 
lation source was a sine-wave oscillator (120 c-200 
kc) . The results of limited tests indicated that the 
generator can do the jobs for which it was designed. 

411-72 (L-900, RP-277) (J. H. Woodruff) . Labo- 
ratory tests of jamming susceptibility of SCR- 
717B (10-cm airborne radar). The artificial jam- 
ming signals were produced by a type 417 reflex 
klystron master oscillator followed by a type 411 
klystron power amplifier and modulator. Sine-wave 
and noise AM and FM were used. Except as to its 
video amplifier this rad^r was found to be generally 
satisfactory with respect to its ability to operate in 
the presence of enemy jamming. A new video 
amplifier was built and found to be 15-20 db less 
susceptible to jamming than the amplifier in the 
radar system. The i-f amplifier was difficult to over- 
load, a good AJ feature. The high-power magnetron 
and high-gain antenna array tend to make effective 
jamming difficult. The AFC is a useful AJ measure 
except when the jamming is strong enough to take 
control. Reducing the receiver gain reduced the 
vulnerability by 5-10 db. The report includes photos 
of screen images, suggested AJ procedures, and cir- 
cuit diagram for new video amplifier. 

411-66 (P-100, RP-246) (H. C. Pollock). Air- 
borne jamming operations against EW and GCI 
radars and v-h-f communications at Orlando, 


404 


APPENDIX 


Florida. The equipment in each of three AT- 18 
planes comprised one B-2000 (against SCR-270), 
two B-2200 (against SCR-588), and one modified 
SCR-522 which was not strong enough to jam v-h-f 
communications satisfactorily. The results in jam- 
ming the radar systems, as detailed in the report, 
were eminently successful. 

411-98 (Z-1800, RP-172) (J. H. Woodruff, 

A. Keck). Field tests of an airborne ASG radar 
jammed by a ship-borne L-105 transmitter indi- 
cate that the L-105 should be an effective source of 
jamming signals. Good radar operating techniques 
reduce jamming effectiveness by as much as two- 
thirds. The techniques include frequent adjustment 
of pain control in homing on a normal target and 
detuning the local oscillator for protection against 
narrow-band jamming, as well as the use of AJ 
devices. 

411-146 (L-1500, RP-436) (F. P. Cowan, R. H. 
Hoglund, D. R. Scheuch). Reports on the extreme 
jamming vulnerability of Mark 31 radar-controlled 
missile. The receiving system is very susceptible to 
both modulated and unmodulated jamming, largely 
because of i-f overload aggravated by the action of 
the AVC circuit. A suggested AJ measure is that 
the i-f gain be reduced and the video gain be in- 
creased, thus making the receiver less susceptible 
to overload by continuous wave. The report includes 
a brief description of the Mark 31 and a discussion 
of the experimental procedure. 

411-131 (E-2200, RP-355) (F. P. Cowan, R. H. 
Hoglund, D. R. Scheuch). Investigation of Navy 
radar homing bomb [RHB] shows that its elec- 
trical circuits are extremely vulnerable to c-w and 
modulated jamming, being made completely inoper- 
ative by a J/S ratio of less than 1 for continuous 
wave. No recommendations are made for AJ modi- 
fications. The device might be adapted for RCM 
use against Japanese 10-cm radar. The report de- 
scribes RHB and includes block diagram, response 
curves, etc. 

411-205 (E-3000, RP-452) (F. P. Cowan, K. A. 
Davis, J. H. Woodruff). Finds that the jamming 
susceptibility of AN/APQ-5B blind bombing at- 
tachment is somewhat greater than that of the 
SCR-717B radar from which it is operated. Per- 
formance is improved by using a short-time-con- 
stant coupling circuit, for which field installation 
instructions are given. 

411-219 (E-3100, RP-453) (H. 0. Anger). Finds 
that the jamming susceptibility of AN/TPL-1 
ground-based searchlight-pointing radar is of rela- 
tively slight degree, except for off-target jamming. 
The generally satisfactory performance is con- 


sistent with the AJ measures which have been built 
into the set. The direction of the jammer can be 
accurately found for all types of jamming except 
when the modulation is closely synchronized to the 
spinning rate of the radar dipole. A small amount 
of off-target jamming causes angular errors suffi- 
cient to throw the controlled searchlight off target. 

411-214 (E-2600, RP-368) (J. W. Woodruff, F. P. 
Cowan). Reports on the jamming susceptibility of 
AN/APG-1 autotracking, gun-laying radar. It also 
describes a field modification to eliminate a range- 
gate jitter which caused unsatisfactory operation 
of the set as originally received. The modified set 
was found to be more vulnerable than a nonauto- 
matic radar, but less vulnerable than the automatic 
RHB and Mark 31. 

411-215 (E-2800/E-2900, RP-449) (R. H. Hog- 
lund). Reports on the jamming susceptibility of 
AN/APS-4 radar and APA-16 bombing attachment. 
The APS-4 displayed extreme vulnerability which 
was decreased by adding a short-time-constant 
coupling circuit. The use of grid-voltage control of 
gain and modification of the AFC are recommended 
to improve the overload performance. The suscepti- 
bility of the APA-16 is the same as that of the 
APS-4, except that angular errors may occur dur- 
ing off-target jamming. 

411-183 (E-2300, RP-367) (J. H. Woodruff). 
Reports on tests of jamming susceptibility of SCR- 
720 A and finds that jamming does not greatly im- 
pair the effectiveness of this radar. Accurate homing 
on the jammer is possible at all ranges. It is esti- 
mated that a heavy bomber should show through 
jamming at about 1 mile. It is recommended that 
no further AJ modifications be made beyond the 
addition of manual r-f gain control as proposed by 
Aircraft Radio Laboratory. 

411-231 (E-3300, RP-475) (J. H. Woodruff, 
H. 0. Anger, K. A. Davis). Reports the results of 
laboratory and field tests of the jamming suscepti- 
bility of SCR-545 fire-control radar using a 200-mc 
system to search and either put a 10-mc system on 
the target, if the 10-mc signals are strong, or auto- 
matically track in range and azimuth, if the 10-mc 
signals are weak. Jam-to-signal ratios of 16-33 db 
for continuous wave, 10-18 db for 100-kc sine wave, 
and 6-8 db for noise were found necessary to jam 
the microwave receiver. In the autotracking cir- 
cuits, ratios of 0 db were found to destroy azimuth 
accuracy and about 5 db to destroy range tracking. 
The azimuth and elevation of the jammer could be 
accurately determined. The search receiver was 
found to be relatively unsusceptible if a fast time- 
constant coupling be added. 


ANTIJAMMING 


405 


411-TM-56 (H. 0. Anger). Discussion of AJ 
practice, description of, directions for installation, 
photos, and drawing of plug-in AJ high-pass filter. 

Div. 15 RP-224 Navy 1.42 for CW55AAB 

RRL E-510 

This device protects against lovr-power continuous 
wave and low-frequency modulated jamming of 
Mark III, Mark IV, and SCR-296A radars by re- 
moving the modulation from the jamming signal. 
It consists of an octal adapter socket to break the 
grid lead to the last video amplifier tube, a pair of 
shielded leads to a toggle switch mounted on the 
front panel of the indicator unit, and a resistor and 
condenser constituting the filter and mounted on 
the switch; by interchanging two resistors a 2 psec 
or a 4 psec time constant becomes available. The 
unit can easily be installed by maintenance per- 
sonnel. In the hands of a well-trained operator it 
will not only accomplish its stated purpose but will 
also help slightly in reading through other types of 
modulated jamming signals. 

411-IB-24. Description and directions for in- 
stallation and operation, with photos and drawing 
of plug-in AJ high-pass filter (RP-171, E-1610). 
This device resembles E-510 in purpose and con- 
struction, except that it is used to improve the 
operation of SCR-268 and consequently has two 
octal sockets to open the grid leads to the two 
parallel tubes of the last video stage. It is designed 
for a time constant of 9 psec. 

411-118 (R. S. O’Brien, W. Y. Pan). Illustrated 
description of recommended changes in i-f circuits 
and reasons therefor, including summary of per- 
formance characteristics and preliminary instruc- 
tions for installation of detector video replacement 
units for SCR-268. 

Div. 15 RP-171 Army BC1324 and 

RRL E-1601,E-1602 BC1325 

The E-1601/E-1602 units are used together to 
achieve improved operation of the SCR-268 in the 
presence of certain types of jamming. These two 
units replace the E-1610 plug-in filter where that 
has been applied. 

411-164 (W. Y. Pan) . Recommends changes in i-f 
circuit of SCR-268 to prevent serious reduction of 
receiver gain following the transmitter pulse. The 
change involves the use of self-bias instead of fixed 
bias in the last two i-f stages, thus avoiding com- 
mon coupling. The improvement is shown by com- 
parative oscillograms. 

411-179 (W. Y. Pan, R. S. O’Brien). Summarizes 
various AJ developments for SCR-268 radar sys- 
tems. These include the E-1610 plug-in high-pass 


filter and the E-1601, 1602, 1602A, 1605, 1606, and 
1607 modification units. ^ 

Antijamming Video Filter Attachment. 

Div. 15 RP-224 Army BC-1375 

RRL E-515 Navy CAOS-50 AEY 

This attachment for Mark III, Mark IV, and 
SCR-296 radars helps to minimize the effects of 
certain types of jamming signals, as described in 
411-TM-87. It consists of a linear diode detector, 
various high-pass and band-pass video filter sec- 
tions, and a two-stage video amplifier. The various 
filters are switch-selectable to pass frequency com- 
ponents of desired pulses and to attenuate undesired 
modulation frequencies. The video amplifier allows 
considerable reduction in the receiver gain, thus 
delaying overload without losing pip amplitude. 

411-TM-87 (H. 0. Anger). Outlines method for 
protecting Mark IV against jammers modulated by 
high-frequency sine wave or narrow-band noise. 
The method involves slightly detuning the radar 
transmitter from the jammer to get a beat fre- 
quency between the two, and then using video filters 
to separate the beat frequency from the jammer 
modulation frequency (or also from the beat fre- 
quencies between barrage jammers). The memo in- 
cludes circuit diagrams and typical oscillograms. 

411-IB-56. Modifications and alterations for 
adapting unit so that it can be used with SCR-296 
radar. 

411-TM-117 (H. 0. Anger, R. S. O’Brien). Dis- 
cusses the principle and effectiveness of detuning, 
summarizes preliminary development work on radar 
AJ detuner (RP-224, E-512). This is an auxiliary 
tuning attachment to facilitate the AJ technique 
of detuning the receiver local oscillator. It is spe- 
cifically designed for Mark III, Mark IV, and SCR- 
296A radars. Presents oscillograms illustrating how 
it helps in the case of continuous wave and modula- 
tion with 50 kc. 

411-TM-51 (E-800, RP-214) (R. S. O’Brien). 
Various AJ devices to be used with the Mark IV 
FD radar. These include a delay line for widening 
the train scope gate, video gain control, high-pass 
video filter, back bias, and local oscillator tuning. 
These devices have been installed for subsequent 
laboratory and field tests. 

411-IB-14. Illustrated description and prelimi- 
nary instructions for installation and operation of 
plug-in AJ high-pass filter (RP-224, E410). This 
video filter coupling circuit improves the operation 
of the ASB series of radar receivers in the presence 
of jamming. It consists of an RC circuit mounted on 


406 


APPENDIX 


a special switch connected to two socket adapters 
to be inserted in place of the detector and first video 
tube, which are plugged into sockets on the tops of 
the adapters. The report includes photos of images 
of c-w jamming, sine w^ave-modulated jamming, 
noise jamming, and sea clutter, with filter off 
and on. 

411-178 (E-400, RP-223) (R. E. Kell). Sum- 
marizes the results of theoretical and test investi- 
gations of the jamming susceptibility of ASB radar 
systems, and suggests various AJ measures. Jam- 
to-signal ratios of 9.6 db (for continuous wave) 
and 2.4 db (for 10 kc sine wave-modulated con- 
tinuous wave) were found to jam a typical receiver 
completely. These ratios were improved by 8 db 
and 15 db respectively after inserting E-410 high- 
pass filter. The receiver’s overload level was in- 
creased 10 db by the E-412 modification of the last 
i-f stage. The system frequency can be shifted from 
that of the jamming frequency by the E-409 remote 
tuning unit for ASB-6 and ASB-7A and by the 
E-413 for the ASB-7B. The E-411 gang tuning 
mechanism, when used with E-409, provides simul- 
taneous control of the transmitter and receiver fre- 
quencies, thus giving single-control tuning for the 
system. These various AJ devices are fully de- 
scribed in the report, with photos, curves, and per- 
formance data on the improvements they effect. 

411-TM-33 (L-900, RP-277) (J. H. Woodruff). 
Two new antijam video amplifiers for the SCR- 
717B. One involves a production line change and 
the other indicates changes which can be made in 
the field. AVith the present amplifier, noise jamming 
need be only 1 db stronger than the echo to obscure 
it, whereas with the new amplifier the ratio is 16 db. 
The new features are an optional short-time- 
constant coupling circuit and the use of a pentode 
instead of a triode limiter. The report includes 
circuit diagrams and detailed discussion for both 
amplifiers. 

411-46 (RP-277, L-901) (J. H. Woodruff). The 
AJ video amplifier for SCR-717B. This unit is de- 
signed to replace the video amplifier in the 
SCR-717B radar equipment. The new unit mini- 
mizes the effect of certain types of jamming and 
sea echoes and, under normal operating conditions, 
provides a better video picture on the scope. Its 
higher overall gain permits decrease in i-f gain with 
consequent increase in jamming power necessary 
for i-f saturation. The use of a sharp-cutoff pentode 
instead of a triode limiter minimizes overload and 
base line displacement. The h-f response extends to 
5 me instead of to 1 me. The unit uses the same 
mounting holes as the original and is easily in- 


stalled. It employs two optional short-time-constant 
video couplings. Results of field jamming and labo- 
ratory tests show that the replacement amplifier not 
only reduces the vulnerability to jamming by 15-25 
db, but also gives an improvement over the original 
in normal operation. 

Range Indicator for Navy Mark IV Radar with 
AA^indow. 

Div. 15 RP-406 

RRL E-2106 

This attachment aids in determining the range of 
moving targets that would ordinarily be lost in 
AAfindow or ground clutter. The obscured targets are 
located by searching in range until characteristic 
audio doppler or propeller modulation is heard in 
headphones. After gating a very small section of 
the range, the modulation of any echo in this gate 
is presented to the range operator through head- 
phones. Since the width of the gate is less than a 
pulse length, the approximate range of a given tar- 
get is obtained by adjusting the range control to 
maximize the doppler tone. The unit comprises a 
gate generator triggered by a pulse from the lead- 
ing edge of the range notch, a stage for mixing the 
narrow gate and the video signal, a stage to amplify 
the gated video signal, and filters to remove the 
pulse repetition frequency [prf] and the lobing 
interference of the radar. 

411-170 (H. O. Anger). Complete description and 
discussion of theory of operation, photos, schematic 
diagram, waveforms, and frequency-response curve. 

411-274 (E-2103, RP-406) (E. R. Brill). Dis- 
cusses several limiter circuits for use with intensity- 
modulated indicators in radar systems employed in 
tracking targets through clutter-infested areas or 
in the blind bombing of complex land targets. AAfiien 
such indicators are operated with conventional 
linear limiter circuit their dynamic range is insuffi- 
cient to allow simultaneous presentation of very 
strong and very weak echoes without saturating 
uniformly on all signals above a certain rather low 
amplitude. The range can be greatly extended by 
using nonlinear circuits in the video amplifier to 
compensate for the cube-law transfer characteristic 
of a cathode-ray tube. One type of circuit employs 
two shunt diodes as the nonlinear elements and 
another type employs a crystal rectifier. The re- 
port recommends that these two types of signal- 
amplitude compression circuits be tested under 
operating conditions. 

411-TM-25 (E-601, RP-213) (D. R. Scheuch). 
Means for distinguishing real aircraft echoes from 
artificial echoes, such as those due to AVindow. 


ANTIJAMMING 


407 


Toward this end are summarized the results of tests 
to detect the 50- to 160-c modulation caused by the 
rotation of the propellers. This a-f modulation 
could not be satisfactorily reproduced because the 
receiver of the Navy Mark IV was not sensitive 
enough and because of difficulty in filtering out 
unwanted frequency components in the echo output. 
Synthetic Giant Wurzburg, 565 me (Adjustable 
540-565 me). 

Div. 15 RP-179 
RRL E-llOO 

Various modifications of an SCR-545A radar 
permitting partial simulation of a German Giant 
Wurzburg with a peak power of 5 kw (adjustable 
3-15). The salient characteristics are as follows: 
prf 1750 per second, average pulse width 2.2 psec, 
lobing rate 25 per second, antenna gain 875, lobe 
split 3 degrees, lobe width at half power, 3.3 de- 
grees, maximum range 55,000 yd. 

411-81 (F. P. Cowan). Describes new units and 
changes in old units with photos, circuit diagrams, 
and sketches of components. 

411-81A (J. F. Youngblood, C. M. Daniell). 
Describes later modification of antenna to permit 
90-degree elevation and 360-degree rotation. 

411-77 (G-606, RP-318) (P. J. Sutro). Photo- 
graphic integration or the use of a long-persistence 
screen is found theoretically to improve the visi- 
bility of a weak signal through noise on an A scope 
(deflection modulation). Either method overcomes 
the lack of homogeneity in the pattern that makes 
direct visual observation difficult. Short exposure 
photographs should bring out the contrast at the 
base line. For longer exposures the camera should 
be adjusted to emphasize the contrast at large de- 
flections. The long-persistence screen would be used 
with an (added) intensity-modulated circuit to 
decrease the beam intensity at small deflections; 
the screen should be viewed through a filter to 
eliminate the “flash.” An artificial overload in the 
receiver may help in distinguishing a weak signal. 

411-84 (E-605, RP-318) (E. R. Brill). Discusses 
the use of long -persistence cathode-ray tubes versus 
[ffiotographic integration of pulses as a means for 
improving the readability of echoes through noise 
jamming of early-warning radars. It finds the long 
afterglow tube to be more practical for combat use. 

411-39 (E-604, RP-213) (E. R. Brill, C. Gray, 
A. M. Hughes, 0. G. Villard) . Describes equipment 
and methods for still and cine-photography of vari- 
ous types of oscilloscope patterns observed in RCM 
and radar operations. Photographs and pertinent 
data of typical indications are included in the 
report. 


411-TM-32 (E-605, RP-318) (E. R. Brill). Dis- 
cusses the usefulness of long -persistence screens as 
a countermeasure against Window and concludes 
that the method is worth further investigation. 

411-TM-124 (E-2000, RP-214) (F. P. Cowan). 
Illustrated description of experimental installation 
of SC indicator, OAV signal generator, and 
CG46ACG for AJ studies, and of a simple method 
of using these components for AJ training. 

411-94 (Z-2500, RP-387) (F. P. Cowan). Dis- 
cusses the RRL training course in defensive counter- 
measures for a selected group of Navy officers. The 
report explains the plan, gives the syllabus, and 
discusses the phases of the work at RRL and Fort 
Lauderdale. 

411-110 (E-1400, RP-343) (D. R. Scheuch). De- 
scribes modifications of SCR-648 used in building 
a synthetic Wurzburg (both small and Giant) for 
testing RCM equipment. The installations are simi- 
lar as regards type of antenna lobing, radio fre- 
quency, peak power, prf, and pulse length. 

411-112 (E-608, RP-318) (E. R. Brill, F. P. 
Cowan) . Discusses the combined use of lobe switch- 
ing for transmission and a single stationary lobe 
for reception as an AJ method for ASB radars. 
A graphical and experimental analysis demonstrates 
that such an arrangement eliminates the scope clut- 
ter (undesirable 1-f modulation of jamming signals) 
and the bearing error in the presence of off-target 
jamming that occur when lobe switching is used for 
reception. The training accuracy is about half that 
obtained with the usual method of lobing for both 
transmission and reception. The improvement is 
illustrated by photos of scope images. Possible ap- 
plications of this technique, which requires more 
complicated antenna installations, are briefly dis- 
cussed. 

411-128 (G-202, RPG82) (D. Middleton, P. J. 
Sutro). Proposes the use of a differentiator circuit 
in the video stage of a radar receiver as an AJ 
system against Chaff (sown radially in the beam 
width). The purpose is to concentrate the target 
return so as to make it visible in the Window dis- 
turbance. The theory of operation, as discussed 
qualitatively and analyzed quantitatively, depends 
upon widening the i-f and video bandwidths suffi- 
ciently to enable successful operation of a modified 
receiver having Type A presentation. The conclu- 
sions are that (1) considerable improvement can 
thus be obtained for pulse lengths of 3 psec or more, 
with little improvement for lengths of 1 psec or less, 
(2) range decreases as pulse width is increased, due 
to mismatched i-f stages and thermal noise from the 
mixer, (3) a single differentiating circuit is more 


408 


APPENDIX 


effective than multiple differentiation in the video 
amplifier, and (4) the method is applicable against 
narrow-band noise jamming when the noise spec- 
trum is narrower than the i-f or video bands of the 
unmodified receiver. The method should be some- 
what more effective against Ropes and Angels than 
against Chaff. 

411-167 (E-2700, RP-447) (J. H. Woodruff). 
Reports favorable results of investigating an AJ 
method for search receivers that are subject to jam- 
ming from an associated spot-jamming transmitter. 
By feeding directly to the receiver a small portion 
of the transmitter output in proper amplitude and 
phase, the jamming picked up on the receiver an- 
tenna is canceled. The parts required comprise a 
line stretcher, two probes, and a cable, which may 
easily be added externally to any spot-jamming 
installation. 

411-207 (E-609/L-1321, RP-214) (J. H. Wood- 
ruff, A. Keck, R. S. O’Brien) . Discusses signal can- 
celation by crossed dipoles as an AJ measure for 
elliptically polarized jamming. The jamming signals 
are received on two separate crossed dipoles with 
outputs properly adjusted in amplitude and phase 


DECEPTION AND CONFUSION DEVICES 


4 1 MECHANICAL DECEPTION AND 

CONFUSION DEVICES 

Chaff. 

Div. 15 RP-103 RRL G-500 

Army AN/CHB, AN/CHA 
Chaff consists of packaged narrow strips of 
aluminum foil designed to be so dispersed that their 
refiection of a radar beam simulates the echo pro- 
duced by a large air or surface craft. The strips are 
machine-cut to a length corresponding to a half 
wavelength of the enemy frequency to be confused. 
Early types were paper-backed, and either flat or 
bent (to stiffen them) . The latest type is made from 
embossed aluminum foil without paper backing; its 
dispersal properties are superior. All types are fur- 
nished in unit packages, each of which simulates 
the echo of one bomber. Later types are taped or 
strung together to facilitate machine dispensing of 
three units at a time. Specifications for AN/stand- 
ard types are: 




Freq. range 

Length by width 

Strips per 

Description 

Type No. 

(me) 

(inches) 

package 

Flat paper-backed 

CHB-0 

110-116 

52x0.25 

50 


CHB-05 

86-230 

60, 48, 38, 30x0.25 

50, 100, 125, 150 


CHB-1 

193-224 

27x0.25 

250 

Bent paper-backed 

CHA-2 

347-404 

15x0.08 

1,000 


CHA-28 

450-600 

111 / 2 , 10x0.045 

1,800, 1,800 


CHA-3 

510-595 

10%6x0.045 

2,000 


CHA-4 

660-770 

7y8x0.045 

3,000 


CHA-5 

2,700-3,400 

1%6x0.045 

30,000 


CHA-6 

8,100-10,600 

i%2x0.045 

300,000 

Bent embossed 

CHA-2-(3) 

335-390 

15 1/2x0.06 

2,200 


CHA-25-(3) 

320-600 

151 / 2 , 12 , 10x0.06 

2,700, 2,700, 2,700 


CHA-28- (3) 

450-600 

111 / 2 , 10 x 0.06 

3,000, 3,000 


CHA-3-(3) 

520-600 

10x0.06 

3,600 

Bent embossed 

CHA-25-(3)T 

Same specifications 

as for corresponding 

untaped type. Used with 

in taped 

CHA-28- (3) T 

G-1107 double tape dispenser. One package 

is equivalent to three units. 

package 

CHA-3- (3) T 





to balance out the signals and thus leave a radar 
echo essentially unaffected by jamming with any 
type of modulation. The correctness of the theory 
was satisfactorily verified experimentally, as shown 
by photos of scope images and by performance 
curves. Investigation of a similar technique for a 
radar with conical scan demonstrated that a fixed 
dipole in an auxiliary reflector gave cancelation at 
one point in the scan. 


411-4 (A-400) (L. J. Chu) . Derives formulas for 
intensity of echo from isolated sphere, disk, rec- 
tangle, cylinder, edge reflector, and corner reflector, 
and applies the results to the problem of producing 
a false echo at 10-, 53-, and 300-cm wavelengths. 
The formulas are derived in terms of an echo con- 
stant {k) which is equal to (R/X)- times the ratio 
of the power density of the echo wave to that of the 
incident wave at a distance {R) of one wavelength 
(A) from the reflector. A single corner reflector is 


DECEPTION AND CONFUSION DEVICES 


409 


found theoretically^ to be superior for ^ = 10 cm, 
and an aggregate of long narrow conductors (length 
approximately 1/2) for ^ = 53 cm and X = 300 cm. 

411-50 (G-500) (F. L. Whipple, W. W. Farley). 
Summarizes preliminary investigations as to mate- 
rials, sizes, amounts, packaging, and production 
methods for a unit of Chaff to simulate the echo 
from a large bomber at various frequencies in the 
range from 100 to 10,000 me. A suitable material 
was found to be thin aluminum foil mounted on 
paper and made rigid by cutting and bending into 
long narrow strips. In the 350- to 1,000-mc range 
a 3-oz package of strips X/2 in length and falling 
2-4 mph was found to simulate one bomber during 
the period that the strips infested the area covered 
by the radar beam. Greater weight per unit and 
much smaller actual lengths were required for the 
1,000- to 10,000-mc range. In the 100- to 350-mc 
range better protection for shorter periods was pro- 
vided by straws^ formed from the paper-backed foil. 
Conclusion was that a skilled radar operator should 
be able to distinguish Chaff echoes from those of air- 
craft. Report includes brief illustrated description 
of rotary cutter for quantity production of Chaff. 

411-73 (G-1400, RP-257) (G. P. Kuiper). Gives 
graphs, photos, and interpretations of field tests of 
the relative effectiveness of six types of paper- 
backed Chaff at 515 me for both vertical and hori- 
zontal polarizations. The chief conclusion is that 
echo fluctuations are governed by a Rayleigh dis- 
tribution throughout a total range of 30 db, the rate 
depending upon the radio frequency and the rate of 
horizontal dispersal. The time of fall through 1,000 
ft is 3 min for vertical polarization and 5 min for 
horizontal polarization. The report includes a de- 
termination of the main lobe of Yagi antennas and 
frequency curves of echo strengths. The general 
conclusion is that the random echo of large infesta- 
tions of Chaff approximates echo of flight of planes. 

411-TM-108 (J. Levine). Tabulates results of 
field dispersal tests of CHA-3 in 15-in. and 6-in. 
wrappers. Average results were about 50 per cent 
dispersal (as compared to 85-100 per cent with em- 
bossed foil) . Additional tests against a radar beam 
showed that echo strength is improved by increasing 
strip width. 

411-91 (G-500) (G. P. Kuiper). Subsumes and 
interprets information on Window presented in pre- 
vious reports and reaches a number of important 
conclusions, including the fact that embossed full- 
hard aluminum foil is better than paper-backed foil 

a It is not yet verified experimentally that a corner refiector is 
superior to Chaff at any radar frequency. 

b Now superseded by “Ropes”; see 411-91. 


as a material for Chaff and Rope. The embossed 
foil does not ‘^nest,” has smaller weight and volume 
per effective unit, and saves paper, glue, and labor. 
It can be cut and bent by existing cutters slightly 
modified and is more effectively dispersed by dis- 
pensing machines. Its rate of fall is from 200 to 
350 ft per minute. Among the facts not mentioned 
in preceding abstracts about Chaff is a simple 
formula for figuring strip length: L = 56 in./F, 
wdiere F is the frequency in 100 me for the principal 
resonance peak. Included curves show that there 
are also secondary peaks at integral multiples of 
the resonance frequency, with heights decreasing 
roughly as the square of the number of the over- 
tone. These curves indicate that the bandwidth 
extends from — 6 per cent to -j- 7 per cent of the 
peak frequency and increases by a factor of 1.2 each 
time that the Chaff width is doubled. No Chaff is 
yet available for efficient jamming of microwave 
radar in vertical polarization, although a new prod- 
uct, CHA-45, may hold the clue to solving the 
problem, utilizing the second and third overtones of 
long strips falling in random orientation. The report 
includes a few remarks and examples on the tactical 
uses of Chaff and on anti-Chaff measures. 

411-236 (F. L. Whipple, A. T. Goble, A. W. 
Tyler, M. Hamermesh) . Comprehensively recapitu- 
lates the development and application of all types 
of mechanical deception and confusion devices, in- 
cluding Chaff, Rope, and Angels. The treatment is 
descriptive and historical and effectively replaces 
all previous reports. New subject matter includes 
the use of projectile Window (in bombs) to identify 
front lines and landing points, an explanation of the 
theory of Window, and an account of the opera- 
tional uses of Window. 

411-TM-127 (G-1800, RP-257) (F. Bloch, 

M. Hamermesh) . Derives equations for the return 
cross sections from random-oriented Chaff. 

411-TM-126 (G-1800, RP-257) (R. D. Sard). 
Computes the response of microwave Chaff for dif- 
ferent polarizations and angles of elevation. With 
horizontal polarization the response is found to be 
sensibly independent of the angle of elevation. With 
vertical polarization the response is near zero from 
the horizon up to about 30-degree elevation and 
then rises rapidly toward a maximum value at 
90 degrees. A system on vertical polarization is less 
vulnerable to Chaff, the advantage over horizontal 
polarization being 32.4 db at 10 degrees, 5 db at 
50 degrees, and 0.6 db at 70-degree elevation. With 
rotating polarization the response varies as the 
plane of polarization is turned and also varies with 
changes in Chaff configuration and distribution. 


410 


APPENDIX 


411-106 ' (F. L. AVhipple). Table of available 
types of Chaff and Rope with information as to 
polarization, frequency band, and weight for each 
type. 

411-103 (G-1800, RP-406) (J. H. Van Vleck, 
F. Bloch, M. Hamermesh) . Discusses mathematical 
theory of the response of Chaff as a function of its 
cross section, which, in turn, is found to depend 
upon the ratios of Chaff length (21) to effective 
radius (a) and to radar wavelength (X) . The quan- 
titative results of two independent solution proce- 
dures are presented in a series of graphs showing 
the mean cross section of randomly oriented Chaff 
and the effect of the angle of incidence on the cross 
section. The mean cross section assumes maximum 
values when 4i/X is slightly less than the “resonant” 
integral values {n = 1, 2, etc.). If d denotes the 
ratio of returned to incident power, the value of 
d/X^ at resonance increases slowly with n, and 
decreases rapidly for nonresonant values of 4i/X, 
reaching minimum values near 3/2, 5/2, etc. These 
minimum values increase as 2l/a decreases. Also, 
the heights of the minima increase and approach the 
height of the resonance peaks as 41/X increases. The 
theoretical results are compared with preliminary 
experimental results. 

411-125 (G-1800, RP-406) (R. Weinstock). 

Finds that the echo cross section of square sheets of 
Chaff is not satisfactory for use as short-wave 
Window, considering the weight-to-response ratio. 
The report also includes a theoretical evaluation 
of broadside echos from circular cylinders, for per- 
pendicular polarization. 

411-174 (G-1800, RP-406) (F. Bloch). Derives 
general formulas for calculating the weight of Chaff 
needed to protect plane formations against projec- 
tiles controlled by radar fuzes (such as me 382) 
by causing the projectiles to explode before reach- 
ing the formation. As an example of the use of the 
general formulas, it is figured that 400 lb give 75 per 
cent probability and 880 lb give 95 per cent proba- 
bility of explosion while flying through 2,000 ft of 
Chaff-infested air. This should be adequate to pro- 
tect a formation over a front 1 mile wide and % 
mile high during 1 min of flight at 200 mph. 

411-199 (G-1151, RP-406) (D. A. Peterson). 
Expendable Chaff dispensers can be hung on the 
bomb racks of fighter aircraft to dispense Chaff or 
Rope from a high altitude in advance of bombers 
requiring protection from enemy gun-laying radars. 
The units are released after serving their purpose, 
thus freeing the fighter for more active duty. An 
inner container is loaded with 350-400 bundles 
which are ejected by aid of a motor-driven stripper. 


an air-intake scoop, and an ejection tunnel. Report 
describes and gives results of flight tests of G-1151 
mounted on P-51 aircraft. At 210 and 240 mph, 
RR 6/U Chaff was dispensed with better than 95 
per cent dispersal, RR 4/U Chaff gave 75 per cent 
dispersal, and RR 3/U Rope appeared to be about 
80 per cent effective. 

Rope. 

Div. 15 RP-257 Army AN/CHR-1 & CHR-IT 

RRL G-1200, G-1800 Navy AN/CHR-1 &CHR-1T 

Rope consists of a roll of ribbon-shaped alumi- 
num foil, 400 ft long and V 2 in. wide, and a small 
parachute (for vertical polarization), or 3-in. 
square card (for horizontal polarization). When 
assembled in packages of three rolls it is used to 
confuse radar systems operating at frequencies less 
than 500 me. CHR-IT differs from CHR-1 only 
in that packages are taped for automatic dispens- 
ing by G-1107. Each package weighs 12.8 oz gross. 

411-TM-28 (G-500) (E. Fubini, M. Hamer- 
mesh). Analyzes the use of metallized Rope as a 
substitute for Chaff. Theoretical conclusions indi- 
cate that Rope should be economically effective 
against EW but not against GCI and GL radar 
systems. For its weight to be comparable to that of 
Chaff, each Rope and parachute should weigh less 
than 1 oz. 

411-TM-lOO (G-1800) (F. Bloch, M. Hamer- 
mesh). Analyzes the effectiveness of Rope in pro- 
ducing vertically polarized radar echoes. The an- 
alysis is accomplished by aid of the Maxwell field 
equations and results in an equation for the cross 
section of the Rope in terms of the wavelength of 
the incident radiation and the length, width, and 
inclination of the Rope. The width is assumed to 
be large compared to the wavelength and the angle 
of inclination is assumed to be small. 

411-TM-lOOA (G-1800) (F. Bloch, M. Phillips). 
Extends the result of TM-100 to cases where the 
wavelength (X) of the incident radiation may be 
less than the width (d) of the Rope. Equations are 
derived for both vertical and horizontal polariza- 
tion and the results of numerical computations are 
plotted in terms of cross section versus wavelength 
for the range from X 314d to X = 0.314d. It may 
be deduced from the curves that Rope is relatively 
ineffective for horizontal polarization at any X/d 
ratio and for vertical polarization at ratios less than 
3.14. Increasing the ratio to 31.4 multiplies the effec- 
tiveness by 3, and to 314 multiplies it by 121/2- Iii 
other words Rope is most effective for vertical 
polarization at long wavelengths. 

411-91 (G-500). Reviews all phases of Window 


DECEPTION AND CONFUSION DEVICES 


4II 


(see Section 4.1 under “Rope”). It states that Rope 
gives 2.6 times the response at 100 me than at 
560 me. Rope is found to be particularly useful 
when enemy frequencies are not known in advance 
or are widely scattered. The report includes oscillo- 
grams of a large number of Rope echoes in both 
vertical and horizontal polarization. 

411-TM-125 (G-1800, RP-257) (F. Bloch, 

M. Hamermesh) . Proves that the equations for the 
current distribution over a thin ribbon of width 5 
and a thin cylindrical antenna having an equivalent 
radius a, are identical when a is replaced by s/4. 

411-TM-133 (G-1200) (H. C. Pollock). Dis- 
cusses the production of long lasting radar echoes 
from balloon-supported Rope. Rope is most effec- 
tive for vertical polarization and for the frequency 
range from 50 to 200 me. It may be carried at con- 
siderable speed toward enemy territory by upper air 
currents and appear as aircraft on an A scope. It 
can also be used to signal from an isolated position 
and to determine wind velocities at high altitudes. 

411-TM-136 (G-1400, RP-406) (A. W. Tyler). 
Gives results of field tests of Rope, tuned and un- 
tuned. Mechanical tests showed that the rolls should 
be placed in individual cartons before they are 
packed in sleeves and that the opening shock at 
airspeeds up to 200 mph is absorbed by a 15-ft strip 
of cloth leader properly attached to the foil. Elec- 
trical tests indicated that three 400-ft rolls of foil 
give an echo equivalent to a head-on heavy bomber 
at 140 me, with increasingly larger echoes at lower 
frequencies and with decreased amplitude at higher 
frequencies, dropping to the 3-db point at 500 me. 
CHR-1, used against a vertically polarized system, 
has a useful life equivalent to a rate of fall of 
5-6 mph. CHR-2 used against horizontal polariza- 
tion has an effective rate of fall of 7-8 mph. The 
memorandum includes photos of packaged and 
opened Rope and of screen images for horizontal 
and vertical polarization at various frequencies. 

Angels (G-1500, RP-258) . 

An Angel is a four-sided corner reflector having a 
radius of about 3 ft. It is designed to confuse micro- 
wave radars. 

411-TM-91 (H. C. Pollock, J. Levine). Sum- 
marizes results of field tests in which the reflective 
power of an Angel was found to be proportional to 
the square of its linear dimensions, and, at 565 me, 
to be equivalent to 0.1 the cross section of a heavy 
bomber. 

411-TM-109 (H. C. Pollock). Summarizes results 
of field tests of the echo characteristics of two solid- 
foil and one mesh-foil balloon-supported Angels at 


565 me. The general conclusions were that the 
echoes fluctuate more violently than do those from 
an aircraft and that an increase in the size of an 
Angel causes a gain in echo size and range. 

411-91 (G-500). Reviews all phases of Window 
(see “Rope” under Section 4.1). It explains that 
the use of Angels is necessarily restricted to the 
higher frequencies and that, until the enemy de- 
velops more microwave radars, the same Angel 
causes a much bigger echo in friendly microwave 
radars than in enemy radars. 

411-TM-131 (G-1400, RP-158) (J. Levine). 

Summarizes results of field tests of echoes from 
Angels at 565 me. Comparisons were made between 
3- and 4-ft Angels, a 3-ft Angel and an AT- 18, 
and both Angels and CHA-3 and an AT-11. In the 
size range considered the equivalent echo area of 
an Angel at 565 me varies roughly as the square of 
the linear dimensions. The equivalent echo of a 3-ft 
Angel is one-eighth that of a B-17. A 4-ft Angel is 
the equivalent of an AT-11 or nearly one-fourth 
that of a B-17. 

759-16 (RP-269) (G. Sinclair, R. B. Jacques). 
Briefly describes the method for measuring reflec- 
tion patterns from a scale model and presents 
reflection patterns of Angel at 515 me for vertical 
and horizontal polarization for various orientations 
in space corresponding to the manner in which 
Angels normally fall. 

(February 14, 1944) 

759-17 (RP-269) (R. B. Jacques). Presents 

reflection patterns of Angel at 360 me. 

(February 18, 1944) 

759-18 (RP-269) (R. B. Jacques). Presents 

reflection patterns of Angel at /fO me. 

(February 20, 1944) 

759-19 (RP-269) (R. B. Jacques). Presents 

reflection patterns of Angel at 1,000 me. 

(February 18, 1944) 

759-25 (RP-269) (G. Sinclair, R. B. Jacques). 
Gives results of reflection measurements on wire 
grids and mesh Angels at 2,000 and 3,000 me. A 
derived formula for calculating the reflection from 
wire grids is practically confirmed by the measure- 
ments, which seem to show that the reflection is 
independent of the polarization. Because large mesh 
sizes are found to be practically transparent to 
waves of a frequency at which small mesh is 
opaque, it is concluded that mesh is effective in the 
construction of a frequency-selective reflecting de- 
vice. Corner action seems to become poorer as the 
mesh becomes larger. 

(August 16, 1944) 


412 


APPENDIX 


931-1 (H. C. Pollock, F. L. Whipple) . A special 
report on field tests of Windoio against SCR-268 
and SCR-270 at Florosa Field and against two 584 
systems and a laboratory model XTIA at Camp 
Davis. The latter tests are considered quite favor- 
able as regards the use of Window. 

(July 6, 1943) 

931-4 (RP-258) (W. K. Kearsley). Tells of ex- 
periments in developing Angel corner folding re- 
flectors, 6-ft structures weighing less than 1 lb and 
launchable from a plane through a 5-in. opening. 

(September 7, 1943) 

931-27 (RP-258) (W. K. Kearsley). Describes 
the construction of Angel corner reflectors. The re- 
flecting surfaces are of aluminum foil; the four 
arms of the frame are of bass wood; the central 
vertical member is paper shellac tubing. 

(September 26, 1945) 


^2 ELECTRICAL DECEPTION AND 
CONFUSION DEVICES 

411-102 (RP-210, D1400) (J. P. Woods, R. 0. 
Petrich). ‘‘Stardust” pulse repeater, 520-570 me, 
consists of a five-stage u-h-f tunable amplifier that 
is used to amplify and retransmit received pulses 
without distorting their shape, thereby causing a 
small target to appear to be very large. The re- 
peater transmits a 20-mc bandwidth with a power 
output of 5 w" for continuous wave or of 15 w for 
pulsed signals. 

895-9 (RP-252) (H. 0. Peterson, W. H. Bliss). 
Briefly describes three proposed DF deception sys- 
tems to provide ship security during ship-to-ship 
and ship-to-shore communication. The systems are 
(1) meaconing, (2) noise masking, and (3) flash 
telegraphy, with (2) and (3) under consideration 
as the more promising, provided that a speed of 
200-400 W'ords per minute is adequate for (3) . 

(October 3, 1945) 

895-40 (RP-252) (H. 0. Peterson, AV. H. Bliss, 
G. S. Wickizer, G. L. Usselman). Describes the 
Blanket mashing signal system to obviate the need 
for maintenance of radio silence by a ship at sea in 
order to prevent DF detection of its position. The 
masking signal transmitted from a 5- to 15-kw 
land-based station is a noise-modulated carrier 
which is broken at a regular rate by short gaps of 
no radiation. On the same carrier frequency the 
ship transmits pulses at the gap rate, properly 
phased to arrive at the land-based station during 
the gap intervals when the ship signals can be 


received. At all points beyond and to the sides of 
the ship the two signals are so mixed that the ship 
signal is concealed. Results of two extensive tests 
indicate that further development is required in 
order to provide reliable communication over a 500- 
to 2,000-k range spread over a 180-degree sector 
about the masking station. 

(October 3, 1945) 

931-2 (RP-156) (S. Hansen, H. H. Race) . De- 
scribes field tests of Peter installed on a 75-ft boat 
in Chesapeake Bay and employed to confuse an 
ASB operator on a PBY-5 trying to home on the 
boat. The tests indicated that Peter gives real pro- 
tection to small boats and submarines from air- 
borne radar-controlled night attacks. (Peter is 
essentially a wide-band r-f amplifier and modulator 
designed to receive and amplify pulsed enemy 
radar signals and modulate the return signal so as 
to deceive or confuse an enemy radar operator and 
prevent his obtaining a true bearing indication for 
gunfire control.) 

(August 24, 1943) 

931-3 (RP-156) (S. Hansen, H. H. Race) . Gives 
results of flight tests of Peter against FD equipment 
at RRL. Fully automatic operation (with no indi- 
cation that normal echoes were being modified) was 
realized up to 5 miles horizontal range at 5,000-ft 
elevation. 

(September 22, 1943) 

931-8 (RP-156) (S. Hansen) . Presents the theo- 
retical considerations involved in the design of a 
multichannel amplifier with grounded grids for 
covering a 20-mc bandwidth, such as is required for 
Peter. 

(February 10, 1944) 

931-10 (RP-156) (H. H. Race, S. Hansen) . Gives 
results of flight tests of Peter equipped with two 
new types of modulators and working against a 
synthetic Giant AA^urzburg (rotating polarization). 
Type E, which generates a sine w'ave automatically 
synchronized and manually phased with the radar 
lobing rate, produces a fixed error of 1.6 degrees or 
38 per cent of the total beamwidth. Type F, which 
generates a random wave containing components 
uniformly distributed in a narrow band bracketing 
the radar lobing rate, produced in the radar bearing 
an uncertainty zone of 1 degree or 24 per cent of 
the total beamwidth. 

(July 14, 1944) 

931-25 (RP-156) (S. Hansen) . A comprehensive 
exposition of the purpose, design, construction, and 
operation of Peter. Experience indicates satisfac- 
tory technical performance in rendering GL radars 


TEST AND TRAINING EQUIPMENT 


413 


ineffective. Tactical requirements are found to be 
better met by jammers except for unusual cases 
such as proximity fuze countermeasure. 

(November 16, 1945) 

966-54 (RP-422) (K. L. Maurer) . Discusses the 
effectiveness of various types of countermeasures 
against Japanese high-frequency DF systems and 
suggests equipment suitable for this application. A 
jammer equipped for automatic tracking is thought 
to be more effective than a meacon (a device which 
receives and rebroadcasts DF transmission at the 
original frequency, thereby causing an erroneous 
bearing at the DF station, since the field is the 
resultant of the original and rebroadcast fields). 

(July 7, 1945) 

966-55 (RP-422) (K. L. Maurer). Surveys the 
basic technical considerations that govern counter- 
measures against radio -navigation aids. General 
principles, including discussion of wave propaga- 
tion, various antennas, direction finding, and range 
finding, are reviewed. Jamming and meaconing are 
described for various applications. Brief mention is 
made of methods for anti-countermeasure. 

(October 15, 1945) 

1045-MR-6 (RP-995) (D. K. Reynolds). Dis- 
cusses the design construction and operation of a 
proposed communications deception device, Elmer, 
designed to provide automatic operation of one 
transmitter so as to simulate a net of several trans- 
mitters having different output powers and fre- 
quencies. It may be used with SCR-284, SCR- 193, 
and/or SCR-506, in conjunction with a magnetic 
wire recorder containing information which auto- 
matically turns them on or off and keys them in 
accordance with the originally recorded signals. 

(May 15, 1945) 

1305-4 (RP-384) (0. H. Schmitt). Analyzes the 
control mechanism of German BlVh tank, which 
is loaded with an explosive charge and remotely 
directed by radio. The mechanism consists of a 
receiver and audio filter unit; a master-control, 
power-supply, and junction-box unit; a decoding 
unit; a detonation sequencing unit; a gear shift 
sequencing unit, and a hydraulic control unit. Each 
of these is illustrated and described. 

(January 10, 1945) 

1305-12 (RP-334) (J. Mead) . Describes and 
gives the results of a-m jamming tests of fm radio 
altimeters. About 300 w of jamming power wdll 
cause a German FUG- 101 to indicate too low an 
altitude, whereas 50 kw might conceivably be nec- 
essary to jam AN/ARN-1 and AN/APN-1 if used 
as proximity detonators. Because of the lack of a 


balanced detector, the German instrument is more 
vulnerable than the two American types. The report 
describes the characteristics of these three types of 
instruments and discusses possible power require- 
ments in tactical situations. 

(April 30, 1945) 

1458-1 (RP-445) . Recommends a field test pro- 
gram for deception of the Japanese h-f DF system 
in the 2- to 20-mc band. This DF equipment is of 
the elevated H type with crossed antenna and with 
receiver installed between the four fixed dipoles. 
The operator at the receiver position takes bearings 
with a hand-operated goniometer having an aural 
null. The proposal calls for the investigation of the 
polarization of sky waves and the development of 
a meaconing transmitter provided with frequency 
scanning and monitoring means. 

(June 12, 1945) 


TEST AND TRAINING EQUIPMENT 
5 1 SIGNAL GENERATORS 


411-TM-971 Test oscillator, 40-3,000 me (A. 


Peterson) . 

Div. 15 RP-195 

RRL U-500 

General Radio P-523A 


Army TS-47/APR 
Navy TS-47/APR 


This compact instrument is used for testing and 
tracking receivers operating in its frequency range, 
such as AN/APQ-1, AN/ APR-2, /APR-4, or 
/APR-5. It is calibrated for the fundamental 40- 
to 500-mc range in two bands (40-115 and 115-500 
me) , and has usable harmonics up to 3,000 me. The 
signals can optionally be unmodulated or modulated 
with 1,000 c at approximately 50 per cent or with 
pulses (70 psec with pulse-repetition frequency 
[prf] of 500 c). It consists of a variable-frequency 
oscillator and a modulator, with an internal a-c or 
external battery d-c power supply. Modulation is 
provided by an audio oscillator which may be con- 
nected as a blocking oscillator to produce pulses. 
It is equipped with a built-in adjustable antenna or 
may be coupled directly to a receiver. 


Pulsed Oscillator, 2,500-3,500 me. 

Div. 15 RP-292 Army TS-82/AP 

RRL A-2651Y Navy TS-82/AP 

This portable instrument was designed for field 
or laboratory checking of AN/APR-5 or /APR-6 
performance in the 3,000- to 3,100-mc range. It 


414 


APPENDIX 


consists of; a 707B velocity-modulated tube in a 
cavity-type resonant circuit, a multivibrator puls- 
ing circuit to put the tube alternately in an oscil- 
lating and nonoscillating condition, a power-supply 
circuit, a small antenna inductively coupled to one 
side of the resonant cavity, and a crystal detector 
loop-coupled to the other side to serve as a monitor. 
The resulting modulation is a pulse about 100 ^isec 
in length with a prf of about 1,000 c. 

411-TM-4 (J. H. Eldredge, R. B. Holt). Tenta- 
tive specifications. 

411-TM-112 (R. C. Raymond). Brief description 
and circuit diagram. 

411-TM-8 Test transmitter. (RP-147, A-741) 
(R. B. Barnas). This portable instrument for 
checking the operation of a search receiver consists 
of an oscillator-modulator unit, a collapsible an- 
tenna, and battery box (or power unit) . It normally 
radiates a small amount of pulse-modulated r-f 
power at the carrier frequency for wRich it is con- 
structed. It supplies a continuous- wave [c-w] sig- 
nal when the modulator tube is removed. 

411-TM-9 Test buzzer. (RP-147, A2107) (H. T. 
O’Neill) . This portable battery-operated instrument 
was used to check the operation of A-2100 radar 
warning receiver. It radiates a small amount of r-f 
energy which can be electrically coupled to the 
antenna rod or magnetically to the interconnecting 
cables by holding it close to either. 

411-TM-94 Audio oscillator. (U-202, RP-315) 
(J. H. Jasberg). Outlines modifications of the 
Model B Hewlett-Packard audio oscillator to adapt 
it for satisfactory use with the AN/APA-6 pulse 
analyzer. The changes include the substitution of 
a precision dial to provide more accurate prf read- 
ings, the addition of high-impedance output ter- 
minals to provide sufficient output voltage to drive 
the sweep of the AN/ APA-6, and modification of a 
standard cradle to permit the instrument to be 
mounted in a standard rack. Each change is shown 
by a circuit or constructional drawing. 

411-TM-12. Carpet tester, 460-600 me. (J. N. 
Dyer) . 

Div. 15 RP-289 Army TS-52/APQ-1 

RRL F-2200 Navy TS-52/APQ-1 

This is a pulsed oscillator or miniature radar 
transmitter for field or shop checking of the locking 
action of AN/APQ-1. The pulses have a width of 
2 psec and a prf rate of 1,500-3,000. The signal is 
transmitted either from a dipole antenna mounted 
on the unit or through 20 ft of lossy cable. 

411-TM-5. Wide-band r-f sweep generator, 100- 
1,000 me (C. B. Clark, J. P. Woods). 


Div. 15 RP-110 Army AN-APQ-8 

RRL D-1308 Navy AN-APQ-8 

This device is used to determine the frequency re- 
sponse of r-f amplifiers, mixers, and filters by show- 
ing the response curve of the unit under test on the 
screen of an external cathode-ray tube. It eliminates 
the need of a signal generator for frequency calibra- 
tion. It operates by changing the frequency of an 
r-f oscillator in synchronism with the horizontal 
displacement of the spot on a scope. The oscillator 
output is impressed upon the device under test. 
The rectified r-f output voltage of the device is ap- 
plied to the vertical deflection plates of the scope 
so that the vertical displacement of the spot is pro- 
portional to the amplitude of the r-f signal. A beat- 
frequency oscillator circuit is employed using the 
outputs of two 3-cm reflex klystrons fed into a 
common wave guide and mixed in a crystal mixer. 
The center frequency of a desired bandwidth is 
changed by adjusting the cavity tuning on the 
klystrons. Frequency modulation of the mixer out- 
put is obtained by modulating the reflectors of the 
klystrons with a 60-c sawtooth voltage obtained 
from the amplified output of a relaxation oscillator 
which also supplies a constant-amplitude sweep 
voltage for the scope. The sweep width is adjust- 
able from zero to 100 me by changing the amplitude 
of the 60-c sawtooth wave. The device is calibrated 
by means of an external w^avemeter. An AVC cir- 
cuit provides a nearly constant output voltage with 
change in frequency. 

IB-78 (RP-306, U-800). Preliminary description 
of the installation, operation, adjustment, and main- 
tenance of test oscillator, 1,500-3,500 me. This cali- 
brated signal generator is designed for general use 
with micro-wave receivers, filters, lines, etc. Single- 
dial calibrated control provides continuous variation 
in r-f frequency. More accurate frequency measure- 
ments may be made from a calibration chart and 
Veedor counter on the panel. Provision is made for 
panel adjustment of voltage necessary for optimum 
oscillation and for panel control of character of un- 
calibrated output, whether continuous or modulated. 
A bolometer and attenuator must be added if accu- 
rate measurement of output magnitude be required. 
The oscillator consists of a calibrated plunger- 
tunable cavity with either a 2K28 or 707-B reflex 
klystron. Pulsing is accomplished by varying the 
cathode or reflector voltage with a pulse obtained 
from a 6V6 in a blocking oscillator circuit. The prf 
ranges from 270 to 10,000 c with resulting non- 
adjustable pulse widths ranging from approximately 
5 to 40 psec. 


TEST AND TRAINING EQUIPMENT 


415 


411-277 (RP-473, U-1500) (W. B. Wholey). De- 
scribes the circuits for the U-1500 pulser, power 
supply, and proposed output attenuating and cali- 
brating system. This field instrument employs a 
2K28 tube as an oscillator to cover the specified 
frequency range in one band and to provide an out- 
put of 200 pw or more. The modulation is either c-w 
or to 10-psec pulses with prf of 45-4,000 c. The 
project was transferred to a manufacturer before 
completion at Radio Research Laboratory [RRL]. 

411-256 (E-3200, RP-221) (R. E. Kell). De- 
scribes an experimental model of the X-band test 
jammer to be used in determining the vulnerability 
of AN/APS-4. (See Section 7.2.) The transmitter 
consists of an experimental A- 131 magnetron oscil- 
lator tunable in the 8,830- to 10,340-mc range with 
50- to 100-w output and the modulator-power 
supply units of a modified AN/APT-4. Auxiliary 
items include an E-1800 modulation signal genera- 
tor, spectrum analyzer, thermistor bridge, and 50-db 
directional coupler. The text informs on the design, 
development, and operation of the system, with 
block and circuit diagrams. 

867-2 (RP-241) (P. S. Hendricks). Describes an 
interim pulsed signal generator for testing RCM 
receivers with a signal similar to that from a radar. 
An r-f oscillator (WE 368AS or 703A tube with 
parallel-line circuit arranged in a circle) with 180- 
to 850-mc range is modulated by means of a pulse 
generator (multivibrator) having 50- to 12,000-c 
range and 1- to 30-psec pulse widths. The oscil- 
lator output is fed to an antenna where the signal 
amplitude and pulse shape are shown on a cali- 
brated oscilloscope. The distance between the 
antenna and the receiver under test gives a com- 
parative indication of the signal strength at the 
receiver. 

(July 2, 1943) 

867-3 (RP-241) (P. S. Hendricks). Describes 
the CBS 166 pulse generator for testing amplifiers 
and associated equipment which must pass pulse 
signals having a steep wavefront. The generator is 
also applicable to modulating low-power r-f oscil- 
lators or amplifiers for test purposes. The frequency 
range is 50-12,000 c with 1- to 30-|isec pulse widths 
and 150-v maximum output level across 1,000 ohms. 
The report includes circuit diagram and construc- 
tional drawings. 

(August 5, 1943) 

923-1 (RP-270) (D. B. Sinclair, R. A. Soder- 
man). Gives operating instructions for P528-A os- 
cillator for testing receivers in the field. 

(December 7, 1943) 


923-3 (RP-160) (A. P. G. Peterson). Gives 
operating instructions for P525-A signal generator 
for 90-250 me (AN/TPQ-T2). 

(June 5, 1944) 


5 2 SPECTRUM ANALYZERS 

Panoramic Spectrum Analyzer, 80-1,000 me. 

Div. 15 RP-175 Armv TS-54/AP 

RRL D-1203 Navy TS-54/AP 

This portable instrument for measuring the 
strength and frequency spread of signals is used to 
adjust a radar jamming transmitter on the ground. 
It analyzes a bandwidth of either 20 or 5 me cen- 
tered at any desired frequency in its range. It may 
be operated either with automatic sweep to show 
the spectral voltage distribution on the screen of a 
cathode-ray tube or with manual tuning for meter 
measurement of the relative energy in any 100-kc 
portion of the spectrum. The device is essentially 
a superheterodyne receiver with an untuned crystal 
mixer, local oscillator, and wide-band i-f amplifier 
followed by a sweeping local oscillator (either 5 or 
20 me), and a second narrow-band (50 kc) video 
amplifier. For panoramic presentation the sweeping 
oscillator is motor-driven and the output of the 
video amplifier is applied to the defiecting plates of 
the cathode-ray tube, which is swept in synchro- 
nism with the tuning condenser of the sweeping 
oscillator. For meter indication the sweep oscillator 
is manually tuned and output of the video ampli- 
fier is measured by aid of a calibrated bolometer. 

411-TM-6 (W. B. Caufield). Specifications. 

411-TM-6A (W. B. Caufield). Supersedes TM-6 
and covers the characteristics, applications, tech- 
nical features, and specifications of the instrument. 

411-25 (W. B. Caufield). Operating principles 
and procedures, specifications, circuit diagram, and 
performance curve. 

411-IB-39A. Illustrated description and prelimi- 
nary instructions for installation, operation, and 
maintenance of RRL production model — block and 
wiring diagrams, characteristic curves, diagrams of 
conversion and functional waveforms, and photos 
of various transmitter spectra observed on analyzer. 

411-292 (J. C. Riley). Suggests several precau- 
tions and techniques for quantitative measurements 
of noise spectra of transmitters, particularly those 
operating at frequencies beyond the normal range 
of D-1203. Such measurements may be made with 
tunable cavities known as echo boxes. 


416 


APPENDIX 


411-96 ^RP-176, H-lOO) (G. P. McCouch, P. S. 
Jastram). Video spectrum analyzer, 100 kc — ^9 me. 
This noise spectrum analyzer measures the energy 
in either an 11 -kc or 33-kc band anywhere in the 
spectrum and, by means of an auxiliary cathode- 
ray oscilloscope, presents a panoramic view of the 
spectrum from 1 to 5 me. At maximum sensitivity 
the analyzer will measure a noise input level of 
3.5 pv/kcl (100-ohm input) or 10/pv/kc^ (50,000- 
ohm input) with gain constant to within 1 db over 
the range from 100 kc to 9 me. The actual sensi- 
tivity is controlled by means of two calibrated 
attenuators fed through a cathode-follower input 
and preceding a 9.5-mc low-pass filter. The instru- 
ment is essentially a wide-range receiver operating 
on the superheterodyne principle with the inter- 
mediate frequency above the region of the spectrum 
to be investigated. The audio output indicator is a 
thermistor bolometer bridge. A regulated power 
supply is incorporated in the unit. The analyzer 
will detect peaks but will not detect narrow holes 
in the noise spectrum. 

411-154 (RP-306, H-600) (P. S. Jastram) . Low- 
frequency spectrum analyzer, 500 c-200 kc. This 
instrument accurately measures the rms value of 
components of the noise spectra in a 60-c pass band 
located anywhere wdthin the rated frequency range. 
It operates on the standard heterodyne principle 
and measures noise levels as low as lOOpv/kcl. 
The instrument comprises an attenuator, a high- 
pass filter, one stage of signal preamplification, a 
modulator and local oscillator, a low-pass filter and 
1-f amplifier, and a rectifier and voltmeter, with 
voltage-regulated power supply. No indication of 
waveform is given. 

931-9 (RP-347) (J. H. Rubel, T. Hudspeth, 
R. E. Troell). Describes a spectrum analyzer for 
the 100- to 1,500-mc range of carrier frequencies 
showing spectra up to 70 me in width. Radio-fre- 
quency signals above 250 pv may be analyzed 
from panoramic presentation on a 5-in. cathode-ray 
tube. The device is essentially a narrow-band super- 
heterodyne receiver whose local oscillator is fre- 
quency-modulated with a 60-c sweep. 

(March 18, 1944) 

931-11 (RP-347) (E. S. Miller, J. H. Rubel). 
Instructs on operation of RP-347 spectrum analyzer 
in producing plot of relative signal amplitude versus 
frequency on cathode-ray tube screen. 

(August 23, 1944) 

931-15 (RP-392) (J. Kahnke, E. Taft, R. L. 
Watters, L. Apker). Describes a double super- 
heterodyne type of spectrum analyzer for the 10- to 
8,500-mc range showing spectra up to 200 kc in 


width. The instrument is tuned over the entire range 
by a single dial, has a 30-db rejection of spurious 
responses, gives a signal-to-noise ratio of 2 with a 
100-pv signal in a 50-ohm line and, by means of 
a 115-mc logarithmic amplifier, presents a constant 
30-mc portion of the band on a 5-in. cathode-ray 
tube. The amplifier handles a 35-db power range. 
Signals feed directly into a crystal mixer, a cascade 
combination of an input crystal, a filter network, 
and an output crystal. Frequency calibration accu- 
rate to within ih 5 me from 500 to 3,500 me is 
furnished by a spark-exeited wavemeter. The 10- 
to 3,500-me range is eovered by using a Z668 tuned 
to 22,000 me as the first loeal oseillator and a 2K33 
tunable from 22,010 to 25,500 me as the seeond 
loeal oseillator. 

(February 1, 1945) 

931-16 (RP-392) (L. Apker). Analyzes mathe- 
matieally the eonversion loss due to reciprocity 
failure in crystal mixers. 

(Mar eh 9, 1945) 

931-17 (RP-392) (L. Apker, E. Taft, J. Diekey) . 
Deseribes the double crystal 7nixer used in the 10- 
to 3,500-me speetrum analyzer and determines its 
behavior in terms of linear network theory with 
matrix equations. Solution of a numerieal example 
for a typieal silieon erystal satisfying the reei- 
proeity eondition shows a eonversion loss of 23 db 
for double mixing. Most silieon erystals are found 
to satisfy the reeiproeity eondition, whereas some 
germanium erystals do not. 

(April 2, 1945) 

931-19 (RP-392) (E. Taft, J. Kahnke, R. L. 
Watters, L. Apker). Deseribes a double super- 
heterodyne type of spectrum analyzer for the 10- to 
1,200-mc hand showing speetra up to 200 ke in 
width. This instrument uses the same prineiples and 
some of the same eomponents as listed in 931-15. 
The charaeteristies of the two instruments are quite 
similar. 

(August 3, 1945) 

931-20 (RP-392) (J. Diekey, L. Apker). Derives 
a formula for eonversion loss and gives results of 
measurements showing the unreliability of the reci- 
procity theorem for welded germanium crystals. 

(September 28, 1945) 

931-26 (RP-392) (R. L. Watters). Deseribes a 
variable-impedanee input circuit for 115-mc i-f 
amplifier having 200-ke bandwidth. The eireuit is 
designed for use in the speetrum analyzer deseribed 
in 931-34. The praetieal range of the variable im- 
pedanee is about 100-2,000 ohms. 

(November 8, 1945) 

931-34 (RP-392) (E. Taft, J. Kahnke, R. L. 


TEST AND TRAINING EQUIPMENT 


417 


Watters, L. Apker). Describes spectrum analyzer 
RP-392K designed to take the place of the analyzers 
described in 931-15, -19. The instrument employs 
type 1462 tubes (revised type 2K50) to cover the 
10- to 3,000-mc range with a single control. Other- 
wise it is quite similar to those it supersedes. All 
spurious responses are suppressed by at least 35 db ; 
approximately 100 me of the spectrum is presented 
at any one time; frequency calibration is accom- 
plished with a K-band wavemeter. 

(November 8, 1945) 

1045-MR-13 (C. B. Clark). Describes modifica- 
tion of AN/APA-11 pulse analyzer to facilitate 
prf measurements. This is accomplished by “open- 
ing” the sine-wave time base into an ellipse, thus 
permitting the base of the pulse to be seen without 
interference from the return trace. The report gives 
circuit changes necessary to provide the elliptical 
time base. 

(May 25, 1945) 


5 3 FREQUENCY METERS 

411-TM-lO (J. F. Byrne). Frequency meter for 
pretuning AN/APT-3, 70-145 me. 

Div. 15 RP-294 Army BC-1255A 

RRL B-2700 Navy BC-1255A 

This portable battery-operated frequency meter 
consists of a local oscillator-mixer tube, two-stage 
audio amplifier, and jacks for headphones or meter. 
A signal picked up on a short-wire antenna is mixed 
with the output of the local oscillator tuned to a 
frequency in the 70- to 145-mc range. The amplified 
beat frequency is applied to a test meter or head- 
phones to indicate its presence. When the local fre- 
quency is identical with that of the signal, the beat 
frequency is zero and the meter dips or the phones 
indicate no signal. The frequency is read to an 
accuracy within ±0.3 me on a calibrated dial. 

411-289 (C. D. Jeffries). Heterodyne frequency 
meter, 55-100 me, 100-250 me. 

Div. 15 RP-245 Army TS-99/AP 

RRL U/B-3000 Navy TS-99/AP 

This portable a-c operated instrument was origi- 
nally designed for pretuning AN/APT-1 in the 60- 
to 225-mc range in a manner similar to that em- 
ployed with B-2700. It was later modified to permit 
field measurement of frequencies in the 100- to 
250-mc range by utilizing the harmonics of the local 
oscillator and of the received signal. It consists of 
a calibrated variable-frequency local oscillator (55- 
105 me and 100-250 me in a butterfly circuit) 
coupled to a diode mixer whose output feeds an 


audio amplifier; it also contains a built-in power 
unit. The energy of the frequency to be measured 
is coupled into the mixer, and the frequency of the 
local oscillator is varied until an audible beat note 
is heard in headphones connected to the audio 
amplifier. The audible beats indicate that the dif- 
ference between the two frequencies is practically 
zero. Because of the many possible beat-frequency 
combinations it is necessary to locate two successive 
dial positions where beats occur, and then to de- 
termine the unknown frequency within an accuracy 
of about 0.25 per cent by the usual harmonic num- 
ber technique. 

411-TM-52 (L. A. Mayberry). Bandwidth ad- 
justment indicator, 0.5 to 7.0 me. 

Div. 15 RP-293 Army TS-92/AP 

RRL U/B-3100Y Navy TS-92/AP 

This device provides a simple means for aligning 
broad-band (0.5-7 me) amplifiers in the field. It 
may be used to align the i-f amplifier of a receiver 
(such as SCR-587, APR-1, or APR-4), the noise 
amplifier of B-2200, or the Dina 100-w power am- 
plifier combination. The unit consists of a crystal 
mixer, low-pass filter, oscillator-mixer, two-stage 
i-f amplifier, peak rectifier, d-c amplifier, and indi- 
cating meter. The general procedure is to tune the 
subject amplifier (being aligned) to approximately 
the desired operating frequency, feed its output to 
the indicator (tuned to a frequency corresponding 
to the desired bandwidth), and adjust the tuning 
and mutual coupling of the subject amplifier to 
indicate maximum output. 

411-TM-95 (RP-293, Y-700) (L. A. Mayberry) . 
Bandwidth adjustment indicator attachment, 0.5- 
7.0 me. This simple device is similar to B-3100 in 
purpose and design except that it requires a suitable 
communications receiver as a selective amplifier in 
determining the bandwidth of a wide-band i-f am- 
plifier. It comprises a crystal mixer, low-pass filter, 
and metering circuit consisting of a copper oxide 
rectifier and test milliammeter for an audio volt- 
meter circuit. Part of the output of the noise ampli- 
fier under test is fed to the crystal mixer to produce 
sum- and difference-frequency components. The 
mixer output is fed to a filter passing the 0.5- to 
7-mc difference-frequency components. These are 
fed to a receiver having a 0.5- to 7-mc tuning range 
and bandwidth not exceeding 100 kc. The receiver 
is tuned to a frequency corresponding to the desired 
bandwidth and the amplifier under test is adjusted 
to give maximum meter reading. 

411-IB-35 (RP-306, r-4000). Wavemeter, 200- 
450 me and 400-700 me, and 700-1,500 me by 
harmonics. This wavemeter is a part of F-2300 and 


418 


APPENDIX 


F-3600 and is used in measuring wavelengths in 
the fundamental range from 0.43 to 1.5 m or with 
harmonics (at reduced sensitivity) down to 0.2 m. 
It is tuned by means of two coaxial units perma- 
nently mounted in a single cabinet with separate 
inputs and a switch to connect either unit to the 
output meter. The output is fed through a crystal 
detector to a lOO-pa meter equipped with a shunt 
resistance connected through a switch to reduce the 
sensitivity. The meter has a reading error of ap- 
proximately 0.6 me per division and an absolute 
error of less than 0.25 per cent. 

411-TM-27 (U-100, RP-327) (M. T. Leben- 
baum). Suggests approved methods for setting the 
frequency of AN/APT-3, /APT-1, /APQ-2, and 
/APT-2, by means of receivers available November 
9, 1944. The general conclusions are that for spot 
jamming the transmitter must be set during flight 
after preliminary approximate setting before take- 
off and that accurate frequency meters are desirable 
in setting for either spot or barrage jamming. De- 
tailed suggestions are given for tuning each of the 
four types of jammers under consideration. 


5 ^ MISCELLANEOUS TEST EQUIPMENT 

411-TM-18 (W. D. White). Transmitter output 
indicator, untuned. 

Div. 15 RP-290 Army CV-9/APT 

RRL F-2305, F-2308 Navy CV-9/APT 

This simple device is used in tuning u-h-f trans- 
mitters to proxide maximum output, as indicated 
by comparative strength of antenna current, or to 
monitor transmitter output during flight. It consists 
of a pickup unit, a control unit, and intervening 
shielded cable. The pickup unit consists of a 2-in. 
antenna mounted near the transmitting antenna, a 
crystal rectifler, and an r-f choke. The control unit 
is mounted near the transmitter and consists of a 
rheostat and a milliammeter jack. The rheostat is 
adjusted to provide readable meter indication and 
the transmitter is adjusted to provide maximum 
meter reading. F-2308 is a simpler and more easily 
mounted model of F-2305. 

411-127 (E. A. Yunker). Short illustrated de- 
scription of CV-9/APT transmitter output indi- 
cator. 

411-127 (RP-290, F-2306) (E. A. Yunker). 

Carpet output indicator, 450-710 me. F-2306 is a 
portable device used as a temporary expedient in 
tuning a Carpet transmitter feeding an AN-132A 
antenna. It is similar to F-2305 except that it is 


hooked on the antenna and picks up the signal 
through a small probe. 

411-TM-39 (R. R. Rhiger, R. B. Monroe) . Radio- 
frequency power indicator. 

Div. 15 RP-306 Army TS-118/AP 

RRL Z-1600 Navy TS-118/AP 

This device gives a comparative indication of the 
power output of an u-h-f transmitter having a d-c 
path through its output coupling circuit. It employs 
a thermocouple (copper-constantan) in series with 
the inner conductor of 200 ft of RG-38/U r-f cable 
across whose output (where no appreciable radio 
frequency exists) is connected a low-resistance 

milliammeter. The meter measures the direct cur- 

rent flowing through the line as a result of the emf 
generated by the thermocouple. Since this emf is a 
function of the r-f power, the device can be cali- 
brated (with correction for skin effect) to show 
meter deflection versus power input. 

411-TM-12 (J. N. Dyer). Carpet checker, 200- 
450 me and 400-700 me, by two-unit wavemeter. 

Div. 15 RP-290 Army TS-53/AP 

RRL F-2300, F-3600 Navy TS-53/AP 

This is a combined modulation monitor, indicator 
of relative power output, and frequency meter for 
fleld or shop checking of jamming transmitters. It 
consists of an untuned receiver, a peak-reading volt- 
meter, and two interchangeable coaxial frequency 
meters. The voltmeter is used with a crystal de- 
tector, alone or with frequency meter, to measure 
the voltage of a pulsed or modulated signal. The 
frequency meter has a reading error of approxi- 
mately 0.6 me per division and an absolute error of 
less than 0.25 per cent. For modulation monitoring 
and power output indication the equipment may be 
used as a receiver without the frequency meter; 
when so used it has a sensitivity of 25 mv for usable 
output. 

867-8 (RP-261) (0. J. Sather). Describes an 
u-h-f power meter to provide a visual indication of 
relative output at frequencies up to 1,200 me. The 
device also furnishes a nonreactive termination for 
a 50-ohm transmission line. The circuit is funda- 
mentally that of a peak-reading meter for measur- 
ing the voltage across a concentric load resistor and 
is calibrated to read the average power dissipated. 
The resistor is cooled by a high-speed blower. The 
inner conductor of the transmission line is brought 
through the resistor and connected to the plate of 
a special u-h-f diode (see 867-3 in Section 6.1). 

(April, 1944) 

High-Frequency Calorimeter Wattmeter, 300-3,000 
me (RP-306, Z-172). 


TEST AND TRAINING EQUIPMENT 


419 


This laboratory instrument measures modulated 
or unmodulated r-f power up to 300 w with an 
accuracy of 5 per cent or better. The readings are 
for average power over a period of at least 2 min. 
The input impedance can be matched to any coaxial 
line or other impedance by means of a double stub 
tuner. Radio-frequency energy from a 50-ohm line 
enters a standing-wave indicator and passes through 
the matching section into a calorimeter load through 
which a hydraulic system maintains a constant rate 
of water flow. The temperature rise of this water, 
as measured by a thermopile, is thus directly pro- 
portional to the power dissipated in the load. The 
standing-wave indicator, by aid of an auxiliary 
oscilloscope, shows the form of the standing wave 
in a short section of the incoming line, thus indi- 
cating the degree of match or mismatch between 
the line and the load. The matching section is then 
adjusted to provide the pattern corresponding to 
the matched condition. The indicator consists of an 
electrically short circular section of 50-ohm line 
slotted to receive a crystal probe mounted on a 
motor-driven flywheel. The resulting rectified volt- 
age from the crystal probe depends upon the distri- 
bution of standing waves in the slotted line and is 
applied to the scope through slip rings and brushes. 
The calorimeter load consists of an 11 -in 50-ohm 
coaxial line (shorted at the extreme end) with a 
brass outside and a hollow copper center conduc- 
tor. The latter is water-cooled on the inside and 
covered with a layer of graphite particles held in 
place by a Pyrex tube on the outside. The hydraulic 
system provides a constant rate of w^ater flow and 
a thorough mixing of the outlet water, whose tem- 
perature is measured by a hot-and-cold junction 
thermopile calibrated with a microammeter. 

411-TM-70 (J. G. Stephenson, R. L. Henkel). 
Complete illustrated description of construction 
and operation. 

411-121 (Q-1400, RP-306) (W. R. Rambo, S. AV. 
Howe). Describes the design and construction of 
a quick-reading calorimeter type water-load for 
measuring r-f power of 1 kw and more in the 250- 
to 800-mc frequency range, with an estimated accu- 
racy of within 10 per cent. The device comprises a 
50-ohm input tapered matching section with crystal 
probe and microammeter for relative power indica- 
tion, a power dissipator consisting of a shorted 
attenuating coaxial line with Cromax resistance 
wire as the inner conductor and water as the dielec- 
tric, a differential thermocouple and microammeter, 
and a circulating water system. The thermocouple 
measures the temperature rise in the circulating 
water, the meter being calibrated for various rates 


of regulated water flow. Reading time for absolute 
power measurement is 45 sec, and for relative power 
(from crystal probe) is instantaneous. 

411-209 (Q-410, RP-169) (W. R. Rambo). De- 
scribes a small calorimeter type r-f wattmeter for 
1,000- to 3,000-mc range with an accuracy esti- 
mated at dz 5 per cent. The instrument gives a 
direct reading of 0- to 50-w r-f power input. The 
power is dissipated in a 9-in. length of coaxial line 
filled with tap water. The low input impedance of 
this attenuating section is matched to 50 ohms in a 
5-in. length of coaxial line of uniform conductor 
cross section having an exponentially tapered titan- 
ium dioxide dielectric. The instrument requires no 
tuning and can be read in 10-25 sec, depending upon 
the rate of water flow. An instantaneous indicator 
of relative power is also provided. The report in- 
cludes photos and drawings to illustrate construc- 
tional suggestions. 

411-246 (U-1200, RP-306) (C. F. Hadley). De- 
scribes a partly developed microwave luattmeter for 
measuring power in a transmission line in the 2,700- 
3,300-mc range. This laboratory instrument em- 
ploys a directional coupler and a double thermistor 
bridge. It can be calibrated to give direct readings 
of incident and reflected power. The report opens 
with a discussion of why this type of measurement 
is more convenient than calorimetric or slotted sec- 
tion transmission line measurements. Complete 
drawings are given for the coupler, with a circuit 
diagram for the thermistor bridge. From experi- 
ments it is concluded that some work has yet to be 
done in eliminating an error present at high stand- 
ing-wave ratios. 

411-247 (Q-1900, RP-306) (L. A. Manning.) 
Describes a self -calibrating thermistor bridge for 
measuring r-f power in the range from 0 to 40 mw 
as read from a calibrated attenuator. The bridge 
operates on the principle of power substitution with 
a single balance control. An accuracy of better than 
5 per cent is obtained, being independent of ambient 
temperature and thermistor characteristics. 

411-280 (Z-1600, RP-409) (R. R. Rhiger, F. M. 
Gager, J. R. Marshall). Considers the coaxial 
thermocouple-lossy line method of r-f power meas- 
urement for determining transmitter output for 
various standing-wave ratio load conditions. The 
construction and calibration of several types of 
thermocouples are also considered. 

411-280A (H. L. Crispell). Describes measure- 
ment of r-f power by the equivalent signal method. 

411-TM-63 (RP-266, U-400) (C. D. Jeffries). 
Noise tube tester (Type 931 and 931A). This in- 


420 


APPENDIX 


strument measures the noise level of the tube and 
indicates its suitability for use. It consists of a light- 
tight holder with exciting light for tube under test, 
two-stage video amplifier, 0.5- to 7.5-mc bandwidth 
diode detector, power rectifier, two 6E5 indicators, 
calibrated potentiometer, and built-in power sup- 
ply. After the exciter light intensity has been ad- 
justed to close the eye of one 6E5, the noise output 
is measured by the percentage of potentiometer 
resistance necessary to close the eye of the other 
6E5. 

411-IB-3 (RP-306, H-300). Noise analyzer, 0.2 
to 5 me. By means of a bolometer output power 
meter this device measures the voltage of the noise 
generated by a constant-current source in the 0.2- 
to 2.5-mc and 2.5- to 5-mc bands, separately and 
together. It consists of an input probe, calibrated 
attenuator, video amplifier, high- and low-pass 
filters with cutoffs at 2.5 me, and. the output meter. 
The accuracy of its measurements is within ± 4 
per cent. 

411-262 (A-9300, RP-461) (J. R. Duggan). De- 
scribes a system for using a commercial communi- 
cations receiver (SX-25) as a noise analyzer. The 
noise is fed to the antenna terminals of the receiver 
(which is adjusted to maximum sensitivity) through 
a cathode follower and attenuator which is cali- 
brated for the frequency range involved in the 
noise spectra. The attenuator may then be set to 
produce the same S meter deflection for each fre- 
quency, all settings and corresponding frequencies 
being recorded. Proper corrections for sensitivity 
variations are made by aid of a signal generator. 
An auxiliary voltmeter may be substituted for the 
S meter if it is not feasible to operate at full 
sensitivity. 

411-TM-45 (J. F. Byrne). ROM test equipment 
summary as of January 1, 1944. 

411-279 (H. W. Belles, H. L. Crispell, F. M. 
Gager). Describes measurement of microwave re- 
ceiver sensitivity by using a test oscillator, lossy 
cable, and a thermistor bridge. The result is given 
in terms of the lowest value of the maximum power 
available from the equivalent signal source required 
to produce a predetermined receiver output. This is 
obtained from the attenuation equivalents of tw’o 
lengths of lossy cable and a power measurement. 

923-2 (RP-270) (A. P. G. Peterson). Discusses 
the behavior of a crystal rectifier voltmeter at ultra- 
high frequencies (300-2,500 me). The crystal is 
mounted in a probe fed by a coaxial cable from a 
source of h-f voltage. The probe is connected to a 
transmission line measuring system which feeds a 


bolometer. The report indicates satisfactory meas- 
urements if proper technique is used in manufacture 
and if suitable measurements of h-f characteristics 
are made. 

(January 7, 1944) 


5 5 TRAINING EQUIPMENT 

Practice Jamming Set, 450-720 me. 

Div. 15 RP-180 Army AN/UPT-1 

RRL F-2800 Navy AN/UPT-1 

This is a ground-based jammer providing five 
types of amplitude modulation used to train radar 
personnel in antijamming techniques. It is a modi- 
fied form of AN/APT-2 permitting separate or com- 
bined modulation with noise (40 kc to 3.5 me) , sine 
waves (50 and 200 kc variable up to 80 per cent, 
and 120 c at 25 per cent), and pulses (1.5 psec, 10- 
100 kc prf ) . Unmodulated carrier power varies from 
8 w at 450 me to 2 w at 720 me. Sideband energy 
and bandwidth depend upon type and degree of 
modulation and clipping. It is operated from 60-c 
power supply. 

411-TR-27. Brief description with block diagram, 
and laboratory report of performance. 

411-TR-27A. Results of laboratory measure- 
ments and tests on a manufactured model, includ- 
ing photos and performance curves. 

411-TM-104 (E. A. Yunker). Brief description 
and comparison with other types of practice jam- 
mers. 

411-TM-104 (RP-180, F-2000) (E. A. Yunker). 
Practice jamming set, 450-720 me. This equipment 
is similar to F-2800 in purpose and construction 
except that it supplies FM (0-200 c with 3-mc 
sweep) instead of noise modulation and supplies 
sinusoidal AM at 50, 400, and 0.8 to 5.2 kc, the 
latter depending upon the frequency of the power 
supply. Operating power at 400-2,600 c is used 
instead of 60 c. Brief description and comparison 
with other types of practice jammers. 

Practice Jamming Set, 175-550 me. 

Div. 15 RP-323 Army AN/UPT-T4 

RRL F-3800 Navy AN/UPT-T4 

This ground-based transmitter is a modified form 
of AN/APQ-2 supplying the same types of modu- 
lation as does F-2800. 

411-IB-61. Illustrated description and instruc- 
tions for installation, adjustment, operation, and 
maintenance, with schematic diagrams, chart of 


TEST AND TRAINING EQUIPMENT 


421 


counter-settings, and chart of energy distribution. 
Oscillator for Practice Jammers, 100 kc or 400 kc. 

Div. 15 RP-348 Army RF-9/ITPT 

RRL r-4100 Navy RF-9/UPT 

This Colpitts oscillator provides sine-wave modu- 
lation for training purposes with AN/APT-2, 
/APT-3, or /APQ-2 when plugged into the second 
video amplifier socket. It modulates at 100 kc, 400 
kc, and twice the power-supply frequency, and 
obtains its powder from the modulator strip of the 
transmitter. 

411-TR-17. Laboratory test report on operating 
characteristics. 

411-TM-62 (E. Barrett). Brief description with 
circuit diagram and photo, and directions for 
plugging in. 

411-TM-104. Brief description and comparison 
with three other practice jammers. 

411-IB-22. Preliminary operating instructions. 

411-14 (RP-207, B-502) (R. J. Pierce). Jam- 
ming signal generator, 100-350 me. This oscillator 
for laboratory study of jamming can be amplitude- 
modulated by internally generated 100-, 200-, or 
500-kc sine waves or by externally generated noise 
or pulses at frequencies up to 2 me. Description and 
preliminary instructions, with parts list, photos, 
and schematic diagrams. 

411-22 (RP-207, B-501) (R. J. Pierce). Jam- 
ming signal generator, 100-350 me. This instrument 
for laboratory study of jamming consists of a 
variable-frequency oscillator with variable r-f out- 
put (0- to 96-db attenuation) modulated by vari- 
able pulses, all indicated by calibrated panel dials. 
The pulse-repetition rate is variable from 500 to 
5,000 c, as controlled by a multivibrator circuit 
whose output is shaped to provide pulse lengths 
varying from 1 to 10 psec. (Two pulses may be pro- 
vided by aid of a time-delay circuit.) The equip- 
ment may also be used as an unpulsed signal gen- 
erator. Description and preliminary instructions 
with photos and circuit diagram. 

Jamming Signal Generator, 2,400-3,700 me (RP- 
191, A-1700). 

This 6-ft rack assemblage is used for laboratory 
testing of radar receivers, for AJ studies, and for 
instructional demonstration of waveforms due to 
various kinds of modulated and unmodulated sig- 
nals. It employs a WE707B low-power r-f oscilla- 
tor with single-dial control of frequency. A wide 
variety of a-m and f-m signals are provided by 
built-in sine-wave oscillator, phototube noise gen- 
erator, and a pulse unit. The output may be ob- 
served by a built-in wide-range (4 me) oscilloscope. 


be measured by a bolometer-wattmeter, and be 
used for receiver testing either by means of an r-f 
attenuator or by pickup from one of three 12-in. 
paraboloid antennas covering the frequency range 
in three bands. 

411-TM-2 (Ralph Hoglund). Brief description, 
specifications, and suggestions for use, with block 
diagram and photo. 

411-IB-18. Detailed description of all compo- 
nents, operating principles and procedures, main- 
tenance, circuit diagrams, photos, and excellent 
oscillograms of various modulation waveforms. 

Antijamming Training Set, 90-270 me. 

Div. 15 RP-160 Army TPQ-T2 

RRL P-525A Navy TPQ-T2 

This portable generator of signals having various 
types of modulation is used in training radar per- 
sonnel in antijamming techniques. It provides fre- 
quency modulation (deviation 5 me or % me at rate 
of 40 to 100 c) , and amplitude modulation with 
noise (3i/^-mc bandwidth), sine wave (approxi- 
mately 80 per cent at 0.1, 0.3, 1, 3, 10, 30, 100, and 
500 kc) , or pulses (6, 4, or 1 psec and prf of 30, 
100, or 500 kc). About 0.5-w output is available 
either at a relatively high-voltage level from a fixed 
coupling loop or at a lower level from an adjustable 
output attenuator. A demountable loop antenna can 
be connected to either output. 

411-TR-23. Brief description, block diagram, 
photos, and summarized results of laboratory per- 
formance tests. 

411-TR-23B. Brief illustrated description and 
report of laboratory tests and measurements of 
manufacturer’s models. A number of changes are 
recommended for improving construction. 

411-TM-128A (D. R. Schueck). Interference 
generator attachment for Mark I trainer. 

Div. 15 RP-313 Navy TS-109/SPA 

RRL E-1300 

This attachment provides various jamming wave- 
forms and means for mixing them with the simu- 
lated radar signals produced by a Mark I trainer 
used to simulate a Mark IV radar. These waveforms 
include 200- to 220-c and 200- to 220-kc sine waves, 
1-psec pulses at 200-220 kc, and random noise. 
Their modulation at a lobing rate of 30 c enables 
an operator to DF on the simulated interference. 
The device consists of an exciter unit with 6AC7 
tubes as sine-wave generators and an 884 as a noise 
source, a video amplifier, a lobe controller, a lobe 
inverter mixer, and a power supply. Explanation of 
operation of circuit and its components includes 


422 


APPENDIX 


specifications, block and circuit diagrams, photos, 
and sketches of waveforms. 

411-TM-124 (E-2000, RP-214). Describes adap- 
tion of Navy SC radar for use in AJ training. 
Jamming Signal Generator, 450-1,000 me (RP-364, 
U-700). 

This equipment produces various types of jam- 
ming signals for training use against the Mark IV 
and Mark XII radar. The signals may be unmodu- 
lated, sinusoidally modulated (AM at 0.15, 150, and 
400 kc) , pulsed (overmodulation on 100- and 500-kc 
sine waves at most carrier frequencies), or noise 
amplitude-modulated with 2-mc r-f bandwidth. 
Provision is also made for superimposing 25% 120-c 
modulation on any other type of modulation in 
order to simulate a jammer with a poorly filtered 
power supply. It has an output of at least 0.1 w 
which is fed through a variable attenuator to a 
dipole antenna that has a fixed bazooka for con- 
version from dipole to unbalanced line. The noise 
source is a 6D4 gas triode. The 450- to 1,000-mc 
oscillator employs a doorknob triode in a butterfly 
circuit. Carrier level is indicated by a 6E5. 

411-TR-42. Brief illustrated description of RRL 
model of U-700 and report of laboratory tests which 
indicated satisfactory operation. 

411-TR-42A. Report of laboratory tests of manu- 
facturer's model indicated satisfactory performance 
except as regards proper calibration and ability to 
withstand vibration and shock tests. 

411-IB-77. Description and instructions for oper- 
ating, adjusting, and maintaining U-700. 

411-282 (W-1800, RP-471) (0. AV. AVhitby) . Ex- 
plains the components and operation of a DF 
antenna trainer, the AN/APA-42T1, for ground 
instruction in using an airborne rotary antenna, 
particularly AN/APA-42, to take bearings on a 
ground-based radar. 

966-43 (R. L. Robbins) . Describes a phonograph 
record of jamming signals (stepped tone, sweep- 
through, spark, random noise, etc.) to be used in 
AJ training of inexperienced personnel. 

(December 7, 1944) 

RCM EQUIPMENT 
ELECTRON TUBES 

747-1 (RP-353). A preliminary report on the 
resnatron development, most of which is dupli- 
cated in 747-2. 

(March 1, 1943) 

747-2 (RP-351a) (AV. B. Fretter, F. AV. Boggs). 
Traces the evolution in the design and construction 


of experimental resnatron high-power oscillator- 
amplifiers in the 20- to 100-cm range. An early 
model was used in Tuba ground-based jammer and 
a later model was installed in other truck-mounted 
jamming stations. The report includes a brief review 
of difficulties due to transit time effects at high fre- 
quencies, an account of methods used in calcu- 
lating the fields in the tube, and a discussion of 
possible applications to television, dielectric heat- 
ing, and high-voltage X rays. 

(September 21, 1944) 

747-3 (RP-351a) (F. AV. Boggs). Recapitulates 
the chronological development of 10-kw magnetrons 
for oscillation in the 43- to 100-cm range. Special 
attention is given to the choice of a cathode ma- 
terial, to reduction of a fluorescent glow in the out- 
put seal, and to methods of cooling the magnet. 
Data and directions are given for constructing a 
tube to oscillate in the 59- to 100-cm range. 

(July 5, 1945) 

867-3 (M. Freundlich). Describes an idtra high- 
frequency diode (158J) suitable for work up to 

I, 000 me and forming the inner part of a standard 
70-ohm coaxial line. The report includes tests which 
indicate no effects due to transit time nor resonance. 
This lighthouse tube is used in the u-h-f power 
meter described in 867-8 (Section 5.4). 

(December 21, 1943) 

931-6 (RP-244) (J. P. Blewett). Discusses the 
design and performance of the ZP-579, a 150-w 
two-anode magnetron that is tunable over the 350- 
to 750-mc range. The development involves the 
solution of the problems of adequate cooling tech- 
niques, external tuning, minimization of cathode 
back heating effects, and modulation techniques for 
barrage jamming. 

(February 14, 1944) 

931-7 (RP-116) (R. B. Nelson, R. A^. Langmuir, 

J. P. Blewett). Describes the construction of the 
ZP-595, a 10-kw two-anode magnetron for opera- 
tion in the 400- to 700-mc range and tunable over 
about 15 per cent of the range. The anode and sec- 
ondary-emission cathode are water-cooled. A com- 
bination of amplitude and frequency modulation 
fits the tube for use in a barrage jammer. 

(February 9, 1944) 

931-33 (RP-116) (R. V. Langmuir, R. B. Nel- 
son). Traces evolution of ZP-595 through conclud- 
ing research stage. Secondary-emission cathode is 
found to eliminate back heating trouble and to save 
cathode power. No conclusive data obtained on life. 

(November 19, 1945) 


RCM EQUIPMENT 


423 


931-12 (RP-396) (N. T. Lavoo). Considers the 
effect of improved output cavity design on the 
amplification characteristics of the L-I4 tunable 
broad-band amplifier, a modified version of the 
ZP-572 “oil can” tube. It is concluded that a small 
signal amplifier having good gain and bandwidth 
characteristics up to 3,000 me can easily be de- 
signed around an L-14 operating on the quarter- 
wave mode. A power gain of ten times is obtain- 
able with a 10-mc bandwfidth, with wider bands 
obtained at reduced gain. The deteriorating effect 
of large signals is yet to be investigated. 

(August 25, 1944) 

931-13 (RP-116) (R. B. Nelson). Discusses the 
use of a gold-copper alloy solder having a melting- 
point at 950-990 C intermediate between the 778-C 
point for silver-copper alloy and the 1082-C point 
for copper. This 3/8 Au-5/8 Cu alloy is satisfac- 
torily used for soldering copper to steel, fernico, 
copper, and gold by techniques described in report. 

(May 30, 1944) 

931-14 (RP-393). Describes a commercially 
available form of housing and ring-type Alnico 
magnet for 6D4 noise source. The report includes 
a nontechnical exposition of the desirable charac- 
teristics of the 6D4 gas thyratron as compared to 
the 931 photomultiplier when used for jamming. 
The 6D4 properly oriented in an optimum magnetic 
field gives a 5-mc spectrum about 25 db higher than 
that obtainable from a 931A, much of whose energy 
is in the 100-mc region. 

(December 20, 1944) 

931-21 (RP-244) (P. H. Peters). Describes a 
magnetron filament regulator which corrects for 
back heating by maintaining constant filament re- 
sistance. The regulator consists of a motor-driven 
Variac control element, a correction signal ampli- 
fier, and a sampling circuit. It can be used with 
any load whose impedance is a function of current 
or voltage to maintain that impedance within ±: 2.5 
per cent against external factors which would 
cause impedance changes in the absence of con- 
trol. The circuit may be modified to act as a voltage 
stabilizer. 

(November 16, 1945) 

931-22 (RP-244) (T. R. Holer. Finds that a 
decay in the efficiency of 5J29 magnetron from 30 
per cent to 20 per cent after 15 hr or more of run- 
ning cannot yet be prevented. Although the cause 
is not definitely established, indications strongly 
point to secondary emission. As efficiencies drop, 
evidence of bombardment strain appears in the 
glass envelope. 

(October 22, 1945) 


931-29 (RP-244, 430a) (J. P. Blewett, G. Kron, 
F. J. Maginnis, H. A. Paterson, W. C. Hahn, J. R. 
Whinnery, H. W. Jamieson). Explains differential 
analyzer techniques in tracing electron paths in 
vacuum tubes. (The analyzer is an electromechan- 
ical device which integrates the fundamental equa- 
tions for electric and magnetic fields and draws a 
picture of an electron path under assumed condi- 
tions.) The methods are applied to a split-anode 
magnetron and to a study of transit time effects in 
lighthouse triodes. The results are useful in pre- 
dicting behaviors and improving performance. 

(November 23, 1945) 

931-23 (RP-244, 158f) (D. A. Wilbur, R. V. 
Langmuir, R. D. Gordon). Tells of the development 
of 90- to 1,500-mc magnetrons rated at 150-w and 
at 1,000-w continuous output. The 150-w series con- 
sists of ZP-579, -590, -666, -584, -646, -676, -675, 
and -677. The 1,000-w series^ consists of ZP-599, 
-647, and -685 and A-131. The report gives detailed 
data on the design and operation of each of these 
tubes, following a discussion of principles applic- 
able to all of them. The lower-frequency tubes are 
of the split-anode type, while those for the higher 
frequencies are of the multivane behavior. The re- 
port includes numerous photos, sketches, and per- 
formance curves. 

(November 23, 1945) 

931-30 (RP-116) (R. B. Nelson). Discusses the 
factors which determine the design, construction, 
and performance of the externally tuned high-power 
ZP-636 magnetron for 100- to 350-mc range. This 
tube is of the split-anode type with double-ended 
coaxial structure. It is tuned by sliding shorts 
symmetrically placed in coaxial lines connected at 
opposite ends of the tube. The cathode is a heavy 
tungsten spiral. Output varies from 3,000 w at the 
center of the frequency range down to 1,000 w at 
the ends of the range. Efficiency is about 50 per cent. 

(November 21, 1945) 

931-24 (RP-430a) (R. D. Gordon). Records the 
development of air-cooled ZP-633 magnetron to 
provide a 25-w output for airborne jammers in the 
300- to 1,500-mc range. The tube has split anodes 
connected across parallel lines which are shorted by 
sliding contacts. Low efficiency at the higher fre- 
quencies suggests that the frequency range be 
covered by two magnetrons of differing anode- 
cathode dimensions. 

(November 21, 1944) 

931-28 (RP-394) (A. M. Gurewitsch, J. S. 

Hickey, E. L. Strempel, W. H. Teare, J. R. Whin- 
nery). Tells of the uncompleted development of a 
5-kw triode for 70- to 350-mc range. The latest 


424 


APPENDIX 


version, L-200, had an indirectly heated barium 
oxide cathode, molybdenum grid, and water-cooled 
anode. 

(December 8, 1945) 

931-32 (RP-116, -156, -157, -158f, -188, -243, 
-244, -258, -347, -392, -394, -430a, -433, -434) (J. P. 
Blewett) . Summaries work done in developing 
magnetrons, noise sources, confusion techniques, 
and spectrum analyzers. In addition to results also 
reported in accounts of individual projects, the most 
noteworthy conclusion is that the echo from the 
ionized gases produced during explosions is useless 
for confusion of enemy radars. The report includes 
many photos, sketches, and performance curves. 

(November 20, 1945) 

931-35 (RP-430a) (R. B. Nelson). Tells of pre- 
liminary development of ZP-652 magnetron for use 
in a low-power airborne jammer in the 10-cm region. 

(November 23, 1945) 

1019-1 (RP-158a) (L. Tonks). Discusses the 
design of electromagnets for 1-kw magnetrons. 
Formulas are derived for the required number of 
ampere-turns in coils and dimensions are given for 
iron cores to be used with ZP-597, -612, -615, -616, 
-638, and -639. For constant power output through- 
out the frequency range it is also found that magne- 
tron voltage should be inversely proportional and 
current directly proportional to the square root of 
the wavelength. 

(June 6, 1945) 

1019-2 (RP-158a) (H. C. Hertha, R. B. Nelson, 
T. C. Swartz) . Traces the various design and con- 
structional steps in the development of ZP-616 
magnetron to give an output of 1 kw in the 760- to 
1,160-mc range. The tube is water-cooled and uses 
a double-spiral tungsten filament, a J-shaped anode 
soldered with a gold-copper alloy, fernico bellows, 
and a fernico-to-glass air-cooled seal. 

(September 27, 1945) 

1019-3 (RP-158A) (H. C. Hertha). Discusses 
the use of vacuum thermocouples in a detector of 
standing waves for frequencies around 1,000 me. 
They provide a sensitive instrument which does not 
easily burn out and which eliminates the use of 
batteries and cures the drifting of readings in a 
bolometer bridge circuit. 

(October 1, 1945) 

1019-4 (RP-158a) (A. H. Sharbaugh) . Describes 
a method for the “cold” testing of magnetrons and 
its application to the study of parasitic resonance 
in ZP-597 magnetron. The study results in elimi- 
nating harmful resonances which had prevented 


continuous output of 1 kw in the 21.5- to 30.0-cm 
range. 

(September 18, 1945) 

1019-5 (RP-158a) (L. Tonks and associates). 
Summarizes the development of Piccolo 1-kw tun- 
able c-w magnetrons for RCM application in the 
500- to 3,600-mc range. The tubes specifically dis- 
cussed are ZP-594 (460-640 me) , ZP-615 (600-840 
me), ZP-616 (760-1,160 me), ZP-597 (1,000-1,400 
me), and ZP-639 (1,710-2,610 me). Mention is 
made of the evolution of 6J21 from ZP-612 to cover 
the 2,500- to 3,600-mc range and of the ^-kw L-104 
to cover the 8,100- to 10,000-mc range. The dis- 
cussion comprehensively includes design of cath- 
odes, anodes, interaction space, tank circuits, tuners, 
and coaxial and wave-guide outputs. The report 
includes many photos and test curves. 

(October 29, 1945) 

1019-6 (RP-158a) (R. A. Dehn, W. H. Teare, 
S. E. Webber). Discusses the design construction 
and testing of the tunable L-104 X-band magnetron 
having a minimum c-w output of 500 w. The tube 
has a doubly tapered wave-guide output and a thin 
untuned mica window. The vane-type anode is of 
double-strap construction with 12 oscillators. Tun- 
ing is accomplished by a “crown of thorns,” each 
thorn being a sector of an annulus shaped to fit the 
inductance part of the cavity. Preliminary tests 
indicate coverage of 8,100- to 10,000-mc range. 

(October 25, 1945) 

1019-7 (RP-158a) (R. I. Reed). Describes the 
development of the cathode, anode, and tentative 
tuning mechanism of the ZP-594 magnetron oper- 
ating in the 500- to 670-mc range. The tube has an 
eight-vaned anode with double-ring strapping and 
a double-helix tungsten emitter and is rated for an 
output of 1,000 w. 

(October 29, 1945) 

1019-8 (RP-158a) (P. W. Crapuchettes, R. I. 
Reed, R. J. Stupp) . Tells of the successful develop- 
ment of the ZP-597 magnetron to operate in the 
1,000-1,400-mc range wdth a rated output of 1,000 w. 
The final tube has a 12-vane anode tuned by a 
plane C-Ring and recessed flat L-Ring actuated by 
a Monel bellows and tuning post arrangement. The 
cathode is a tungsten bifilar filament supported by 
a molybdenum sleeve. The output connection is 
50-ohm coaxial with terminals tapered to permit 
uniform loading with frequency. 

(October 29, 1945) 

1034-1 (RP-247) (E. Labin, M. Arditi, J. Glau- 
ber, M. Charchian). Traces unsuccessful attempts 
to develop a 600-mc sealed-off resnatron on the basis 
of techniques established for demountable tubes. 


RCM EQUIPMENT 


425 


The chief difficulty is due to energy being absorbed 
from the r-f field by unaccounted for secondary 
emission. 

(May 31, 1945) 

1043-1 (NDRC-366) (L. Malter, R. L. Jepsen, 
L. R. Bloom) . Describes a mica window for wave- 
guide output magnetrons. A mica output window 
has lower dielectric losses than has a glass window 
and is less likely to fail at high output powers. 
Reflections are minimized by proper dimensioning. 

(December 5, 1944) 

1043-3 (L. Malter, J. L. Moll) . Discusses the use 
of quartz output transformers with wave-guide out- 
put magnetrons. The use of fused quartz instead of 
a vacuum as a dielectric permits less stringent me- 
chanical tolerances. Performance is found to be 
practically the same for the two types of dielectric. 

(January 15, 1945) 

1943-2 (RP-430c) (R. L. Jepsen. Discusses the 
use of tantalum cylinder cathodes for c-w jnagne- 
trons designed to deliver 100 w at 1,200 v. For a 
short life of about 50 hr tantalum is found to give 
the required high emission and to dissipate back 
bombardment power more satisfactorily than do 
available oxide-coated cathodes. Tungsten is not 
suited for a single-ended cathode with low heater 
current. The report gives details of design which 
may serve as a guide in solving similar problems. 

(January 15, 1945) 

1043-4 (L. Malter). Gives constructional data 
for a K-band wave-guide output magnetron. This 
is an unstrapped tube wherein the use of alternating 
cavities of unequal size gives a large frequency 
separation between the pi and adjacent modes, thus 
favoring pi-mode operation. Data are also given on 
the development of quartz output transformers, 
mica output windows, and other improvements. 

(March 1, 1945) 

1043-5 (RP-430c) (H. C. Hu) . Derives a scaling 
formula for designing new magnetrons by changing 
the number of slots in an existing tube with known 
characteristics. 

(May 15, 1945) 

1043-6 (RP-244b) (L. Malter, R. L. Jepsen, 
L. R. Bloom, H. C. Hu, J. L. Moll). A sequential 
account of the uncompleted development of A- 131 
tunable X-band c-w magnetron for use in airborne 
jammers covering the 8,500- to 10,300-mc range. 
The latest specifications called for an output of 
200 w at 2,000 v. The report is largely concerned 
with a discussion of problems yet to be solved and 
recommendations for paths to be followed in seek- 
ing solutions. 

(November 15, 1945) 


1222-1 (RP-332) (A. L. Samuel, J,W. Clark). 
Recounts the development^ of 2K48 and 2K49 local 
oscillators for 3,000- to 6,000-mc and 5,000- to 
10, 000-mc search receiver operation, respectively. 
The important requirements for these low-power 
vacuum tubes were that there should be no blank 
regions in the frequency coverage and that they 
should be easily tunable. Each is a velocity-varia- 
tion tube of the focused beam reflex type designed 
for use with an external coaxial cavity whose inner 
conductor forms an integral part of the tube. Tuning 
is done with an adjustable piston which varies the 
effective length of the coaxial cavity. The tube con- 
tains an electron gun which directs an electron 
beam through an h-f gap, defined by holes in two 
copper disks, and a repeller electrode which, after 
a critically valued time of transit in the reflection 
region, redirects the ‘^bunched” beam through the 
gap where it delivers energy to the r-f field. The 
report includes laboratory drawings and test speci- 
fications for the finished tubes. 

(February 28, 1945) 

1222-2 (RP-439) (A. L. Samuel). Reports on 
consulting service on and deliveries of 2K48 and 
2K49 tubes. 

(September 28, 1945) 

1357-1 (RP-158b) (W. G. Wagner). Recounts 
the evolution of the sealed-off 6J21 tunable magne- 
tron from the ZP-612 demountable, continuously 
exhausted prototype. Complete information is given 
on the design, development, and pilot production 
of magnetrons delivering 800- to 1,000-w average 
power in the 2,500- to 3,600-mc range. The tube can 
be fully amplitude-modulated, with simultaneous 
FM of the amount required for RCM purposes, and 
can be tuned to any point in its spectrum within a 
backlash limit of 4 me. Features differing from the 
prototype include a broad-band wave-guide out- 
put transformer and glass window, a thoriated 
cathode, and externally actuated tuning mechanism. 

(September 30, 1945) 

1430-1 (RP-158c) (A. K. Wing, A. S. Vander- 
hoof, P. I. Corbell, H. R. Jacobus). Tells of the 
incomplete development of preproduction models 
of 1-kw c-w tunable magnetrons to cover the 600- 
to 840-mc and the 760- to 1,160-mc ranges (ZP-615 
and ZP-616) . 

(September 29, 1945) 

62 ULTRAHIGH FREQUENCY 

OSCILLATORS 

411-11 (A-1501, RP-173) (G. E. Hulstede). De- 
scribes a double coaxial cavity type of oscillator 


426 


APPENDIX 


using a GL~44^ “lighthouse” tube and tunable with 
a single dial from 1,000 to 3,300 me. One cavity 
terminates the tube’s anode- to-grid impedance and 
the other terminates the grid-to-cathode impedance. 
Both cavities are tuned by means of sliding plungers 
connected through metal rods to an external mecha- 
nism wherein a mechanical linkage with an adjust- 
able cam provides proper trackage for the plungers. 
For applications see A-2600, D-1500 (Section 1.2). 

411-38 (J-800, RP-168) (J. G. Stephenson). 
Summarizes results of tests with early experimental 
models of GE-L-3 triode as a c-w oscillator in co- 
axial line tuned circuits. Most of the models were 
efficient oscillators up to 1,000 me, with usable 
power up to 1,200 me, and were tunable from 300 
to 1,100 me. Optimum output and efficiency required 
external feedback in the grid-separation circuit 
(three types described). Maximum power output 
was limited by mechanical distortion of the grid, 
amounting to about 30 w at 600 me. 

411-49 (A-3000, RP-205) (J. G. Stephenson, 
R. L. Henkel). Summarizes results of experiments 
with GE ZP-449 triode as a c-w oscillator in coaxial 
line tuned circuits described in 411-38. Most of the 
tubes tested with external feedback oscillated as 
high as 2,000 me, delivering 25 w at 500 me and 6 w 
at 1,500 me, using a liquid-cooled anode. Tuning 
range extends from 465 to 575 me. Report includes 
measured characteristics, operating notes, descrip- 
tion and diagram of oscillator assembly, and de- 
scription of tuning methods, feedback, and output 
coupling. 

411-TM-139 (A-3100, RP-286) (R. H. Hoglund) . 
Finds that satisfactory oscillation over the 3- to 
6-cm range with 10-mw output can be maintained 
by a magnetically focused velocity-modulation tube 
(Bell Labs. Exp. 1280 CT) in a wide-band wave- 
guide type of cavity. The tube consists of an elec- 
tron gun, two gaps, and a drift tube, with collector 
and disk connections to an external cavity in whose 
hollow center the tube is mounted. The cavity is a 
rectangular wave guide operated with one-half 
wavelength between two tuning plungers driven 
through a gear train to give full tuning range with 
single-dial control. A regulated power supply en- 
ables operation at three separate voltage modes in 
covering the frequency range. The report includes 
performance curves and circuit diagrams. 

411-TM-135 (A-3200, RP-295) (F. A. Record). 
Reviews the difficulties encountered with micro- 
wave c-w power oscillators and discusses possible 
means for avoiding them. Consideration of small 
conventional tubes, telescopic triodes, cylindrical 
tetrodes, magnetrons, velocity-modulated tubes 


(klystrons), and positive-grid tubes (Barkhausen) 
leads to two possibilities: (1) increasing the upper 
frequency of the high-power, high-efficiency tetrode 
and (2) increasing the power and efficiency of the 
high-frequency velocity-modulated tube. Commer- 
cial developments of wide-range-tuned magnetrons 
are under way for frequencies less than 4,000 me. 
Slight progress has been made in developing 
moderate-power klystrons, at low efficiency. A cy- 
lindrical structure is desirable for high power and 
some type of positive-grid operation is advanta- 
geous for high frequency. 

411-184 (A-3200, RP-295) (F. H. Crawford). 
Interprets data developed in studying tunable 
squirrel-cage magnetrons of both the cavity-tuned 
(SD-849) and internally tuned (donutron) types. 
The resulting theoretical picture of their operation 
reveals several strong modes of oscillation. That 
having the longest wavelength is regarded as a 
loaded cavity oscillation. Those having shorter 
wavelengths seem to correspond to various numbers 
of standing waves around the anode circumference. 
The wavelengths of these latter reentrant-line 
modes depend upon the radius of the anode and 
the number and length of the fingers. Steady c-w 
outputs of around 60 w at 6 cm have been obtained 
from the donutron (14 per cent efficiency) with a 
tuning range of approximately 1.3 to 1. 

411-249 (A-3200, RP-298) (M. D. Hare, 

V. Leonard). Describes the materials, mechanical 
processes, and assembly methods employed in 
Radio Research Laboratory [RRL] construction of 
the donutron, tunable squirrel-cage magnetron, 
Models K and L. 

411-252 (A-3200, RP-295) (F. H. Crawford, 
M. D. Hare). Describes the construction and 
operating characteristics of the donutron, a magne- 
tron consisting essentially of a set of interleaving 
metal fingers arranged to form a multisection 
squirrel-cage anode. The tube is tuned by the rela- 
tive axial displacement of alternate anode segments, 
through flexure of one wall of the cavity in which 
the anode structure is supported. The construction 
is much simpler and cheaper than that of a con- 
ventional multicavity c-w magnetron of the same 
power level. This is of the order of 50 w at 40- to 
50-per cent efficiency with a tuning range of 1.5:1 
with power flat at 3 db. The entire tuning range 
can be covered by a single value of voltage and 
magnetic field. The important modes of operation 
are a long-wave tunable cavity mode and a short- 
wave resonant reentrant-line mode. The former can 
be entirely suppressed and the latter enhanced by 
a special phase-reversing anode. The usual troubles 


RCM EQUIPMENT 


427 


due to mode jumping are almost entirely eliminated. 
Modes of 4 cm or less have been indicated in cold 
tests. The report includes many curves and three 
Rieke diagrams. The discussion covers a wide range 
of design parameters. Voltage-current character- 
istics indicate a static impedance of 700-1,500 ohms. 

411-70 (A-3700, RP-321) (G. Hok) . Summarizes 
results of preliminary tests on operating character- 
istics of the AVestinghouse (Sloan) 10-kw tunable 
magnetron. The report includes a description of the 
equipment and the test procedure, an outline of 
the theory of magnetron modulation, and an ex- 
planation of how Rieke diagrams are used to 
determine the load impedance necessary to provide 
optimum performance. The models tested employed 
an aluminum-coated cathode with a tungsten fila- 
ment for supplying the electrons to start emission 
and oscillation. Because maintenance of emission 
from aluminum requires occasional exposures to air, 
the particular tubes used for these tests could not 
be sealed off and required continuous pumping to 
maintain vacuum. The electrodes are placed along 
the axis of a solenoid magnet coil. Frequency is 
varied by a movable tuning ring which increases 
the capacitance between the anode segments when 
moved to the left and reduces the tank circuit in- 
ductance when moved to the right. The generated 
power is transferred into a rectangular wave guide 
by means of a coupling loop. The anode, cathode, 
and tuning ring are water-cooled, while the magnet 
and output seal are cooled by compressed air. The 
modulator provides a noise output up to 1,000 v 
peak to peak, with a 5-mc bandwidth for a 300- to 
1,000-ohm lead. A typical tuning range is from 310 
to 490 me. Cathode emission was found to be gen- 
erally satisfactory, but all tested tubes show in- 
stability over part of the performance range. 

41 1-70 A. A report on later work on the project 
just described. 

411-160 (A-3700, RP-321) (G. Hok). Explains 
seven methods for calculating the approximate 
parameters of u-h-f resonant systems from the re- 
sults of standing-wave measurements. The methods 
are applicable to four-terminal networks, such as 
vacuum-tube tank circuits or systems with distrib- 
uted constants, where direct measurements are diffi- 
cult or impossible. They depend upon finding an 
approximately equivalent circuit in terms of lumped 
constants, from which are derived the relations be- 
tween the parameters and the “cold” impedance 
seen from the output terminals. The values of these 
parameters are then determined from a plot of 
standing-wave measurements by aid of graphs and 
simple formulas. The report reviews the important 


parameters, discusses equivalent circuits' from the 
viewpoints of accuracy and simplicity of analysis, 
investigates experimental procedure and sources of 
error, and presents the analytical foundations for 
the various methods of calculation. 

411-TM-138 (A-3900, RP-295) (F. H. Craw- 
ford) . Gives preliminary results of measurements of 
the noise modulation of ZP 597 at low power levels 
and relatively narrow modulation bandwidth. The 
noise source was a 931 photoelectric tube. The re- 
sults suggest that this magnetron might be usable 
as a source of power for a jamming transmitter at 
a power level of the order of 150 w for frequencies 
from 1,170 to 1,500 me. 

411-TM-138A (A-3900, RP-295) (F. H. Craw- 
ford) . Gives results of measurements of the response 
to noise modulation of a ZP-597 magnetron at 
500-w output near 24 cm and of a ZP-594 at 500- 
to 1,300-w output near 44 cm. Using unsymmetri- 
cally clipped noise from a 6D4 source with high- 
pass filter cutting off at 1.5 me, the 597 gave a 
bandwidth of 44 me, and the 594 a bandwidth of 
6-12 me at half-power points. The report includes 
a description, block diagram, and a noise spectrum 
of the modulator, and tabulated results in terms of 
both the Rieke diagram and the current-voltage 
plot. 

411-185 (A-3900, RP-417) (F. H. Crawford, 
M. Pease). Discusses the use of a magnetic diode 
in the output coaxial line from a magnetron as a 
method of magnetron modulation. The diode acts 
as a variable-impedance tube whose operation de- 
pends upon the presence of a region of very low 
dielectric constant produced by an electron cloud 
rotating around the cathode. Any change in anode 
voltage changes the standing-wave condition in the 
line by changing the diameter of the electron sheath 
around the cathode. As this changes the operating 
point in the Riecke diagram, it changes (modu- 
lates) the frequency and amplitude of the magne- 
tron oscillations. The method provides a high- 
impedance load into which the modulator acts and 
eliminates d-c plate dissipation. The report includes 
theoretical expressions and graphs for results to be 
expected at low r-f fields. 

411-130 (A-4100, RP-417) (F. H. Crawford). 
Preliminary studies of the response to noise modu- 
lation of a ZP-612 tube with gas-tube noise source 
indicate satisfactory modulated powers and 15- to 
20-mc bandwidths, at half-power points, for modu- 
lator voltages of 800-1,100 v peak to peak. Observa- 
tions were made at 2,660, 2,764, and 2,910 me in 
the 10.2- to 12.1-cm tuning range. A high-pass filter 
in the modulator improved the r-f spectra, which 


428 


APPENDIX 


were somewhat unsymmetrical, with rather pro- 
nounced wings. A marked decrease in cathode emis- 
sion was noted during continued use ; it could 
always be compensated for by increasing the fila- 
ment temperature. 

411-235 (A-4100/9300, RP-461, 417) (J. C. 

Turnbull, J. R. Duggan, C. F. Otis, H. W. Welch). 
Describes modulation tests of 6J21 magnetrons with 
sine-w^ave, noise, and pulse voltages. The results of 
these tests were applied toward the development of 
a magnetron for use as a spot jammer wdth mini- 
mum output of 800 w in the 2,460- to 3,610-mc 
range. 

411-172 (A-9000, RP-461A) (J. F. Byrne). De- 
rives equations for the efficiency and output power 
of a Class B power amplifier of noise energy in 
terms of the peak, rms, and average values of exci- 
tation voltage. The performance of push-pull 813 
tubes with 10 per cent clipped noise is computed 
as a typical example. 

411-159 (D-lOO, RP-416) (R. A. Soderman). 
Discusses applications of butterfly circuits for oscil- 
lators in the 100- to 1,200-mc range of frequencies. 
These are used with type 955 or type 703 A tubes in 
the tuning units for APR-1 and APR-4 receivers 
and C-1203 spectrum analyzer, as well as in the 
U-700 and U-1300 signal generators. They are also 
used in the U/B3000 and GR-720 heterodyne fre- 
quency meters as well as in other applications re- 
quiring a moderately high Q, broad-band, selective 
circuit. They are small in size, light in weight, and 
rugged in construction, but may require close toler- 
ances. The discussion covers both symmetrical and 
unsymmetrical butterflies and explains reasons and 
cures for some of the difficulties that arise. The 
report is well illustrated with sketches, photos, and 
circuit diagrams. 

411-TM-lOl (Q-lOO, RP-186) (R. R. Buss). 
Concludes that a random-pulsed triode cavity oscil- 
lator (ZP-522) is a relatively inefficient and ineffec- 
tive jamming source, unless for possible operation 
in a frequency region wffiere no other equipment is 
operable. Constant-rate pulsed operation is almost 
completely ineffective. No appreciable increase in 
average power output or in upper frequency limit 
has been obtainable from pulsed operation, and the 
size and weight of modulator required for the nec- 
essary short, high-recurrence-rate pulses are out of 
all proportion to the amount of power required for 
the oscillator. 

411-83 (Q-200, RP-204) (J. G. Stephenson, 

R. L. Henkel). Presents the results of studies of 
the characteristics and performance of preproduc- 
tion models of the ZP-522 triode used as a c-w 


oscillator and amplifier in coaxial line circuits. AVith 
125-w d-c input the average air-cooled oscillator 
had an output varying from 46 w at 500 me to 
8.5 w at 1,500 me, the upper limit of useful opera- 
tion. Greater power output can be obtained by 
liquid cooling of the anode. The report describes a 
single-tube air-cooled oscillator tunable from 350 to 

I , 500 me and plate-modulated with wide-band noise 
(modified for use in Carpet IV). It also describes 
a push-pull liquid-cooled oscillator delivering 100-w 
output from 500 to 600 me. Operated as a Class B 
amplifier (cutoff bias) the average tube shows a 
7-8 db gain of up to 800 me, with plate efficiency 
of 40 to 50 per cent. Gain up to 11 db at 600 me is 
possible with Class AB operation, but at reduced 
plate efficiency. The bandwidth at 600 me was about 
13 me, between half-power points. 

411-TM-66 (Q-300, RP-204) (R. L. Henkel). 
Reports the results of an investigation of the opera- 
tion of tw^o A2212 (Nehrgaard) tubes in a coaxial 
cavity oscillator. The tube readily delivers 100 w of 
r-f energy at any point between 175 me (50 per cent 
efficiency) and 400 me (30 per cent efficiency) . The 
practical limit for the first mode (V4) operation is 
somewhat less than 500 me. AAude-band plate modu- 
lation is feasible. 

411-TM-65 (Q-600, RP-305) (R. R. Webster, 

J. G. Stephenson). Concludes, as a result of exten- 
sive tests with coaxial line oscillators using light- 
house triodes (ZP-522 and ZP-449) , that wide-band 
modulation is limited by the high effective Q of the 
loaded output cavity (Q varies from 100 to 1,000, 
depending upon the dynamic impedance of the os- 
cillator tube, the characteristic impedance and 
number of quarter wavelengths in the coaxial tank 
circuit, and the degree of coupling of the tank cir- 
cuit to the load, etc.). The bandwidth obtainable 
with plate amplitude modulation can be improved 
from 75 to 100 per cent by simultaneous grid modu- 
lation in phase with the plate modulation, but at 
the expense of linearity. The same improvement is 
given by a combination of plate and out-of-phase 
cathode modulation. The report presents evidence 
in support of these conclusions. Circuit diagrams 
are given for a push-pull ZP-449 oscillator and for 
a single oscillator, both for 500-600 me, and for a 
single 350- to 1,500-mc ZP-522 oscillator arranged 
for grid, plate, or combination grid-plate modula- 
tion. There are also a number of comparative spec- 
trum curves and other pertinent diagrams. 

411-126 (Q-800, RP-378) (AV. R. Rambo, L. D. 
Tuck, S. AV. Howe). Details performance methods 
and results for 1-kw X-12Ji and X-139 beam 
tetrodes (resnatrons) proposed for use as 500- to 


RCM EQUIPMENT 


429 


600-mc ship-borne jammers. These tubes have a 
thoriated tungsten filament in the form of an 
18-wire cylindrical cage, two tantalum grids (con- 
trol and screen) in the form of an 18-wire open- 
ended cylinder, and a copper anode in the form of 
a slotted cylinder, water-cooled in the X-124 and 
air-cooled in the X-139. Electrons pass from each 
filament wire as a radial sheet focused between grid 
wires into the anode slots. The screen grid is oper- 
ated at a high positive potential to reduce transit 
time and also to shield the cathode from the anode, 
enabling anode current to be shifted into proper 
phase relation with anode voltage by adjusting the 
phase of the driving voltage. Coaxial cavities, tuned 
by plungers, extend in both directions from the 
plane of the grid. In its present developmental stage 
the tube is found to be unsatisfactory for the con- 
templated application. Best performance was given 
by an X-124E operating as an amplifier with only 
30 per cent anode efficiency for 1.2-kw output at 
500 me. In the report various redesign features are 
suggested. 

411-116 (Q-1000, RP-169) (AV. R. Rambo, L. D. 
Tuck). Describes experiments with GL-522 as a 
third-harmonic generator. The best result was 3-per 
cent anode efficiency for an output of 2 w at 1,700 
me. Tuning is critical. 

411-241 (Q-2000, RP-286) (J. J. AVedel). Pre- 
sents tuning curves for 2K28 (McNally) tubes in 
radial cavities to oscillate in the 4- to 33-cm range 
of wavelengths. The curves are obtained by theo- 
retical extensions from experimental data and are 
useful in calculating radial cavity dimensions. Tube 
impedance curves are also given for use in designing 
nonradial types of oscillators. Lumper-capacity 
representation of the 2K28 is shown to be valid 
down to wavelengths of at least 7 cm. 

411-175 (G-2600, RP-295) (F. Bloch) . Analyzes 
the stationary states in a cylindrical magnetron 
when a steady voltage is turned on to maintain a 
small current. The solution is based upon con- 
sideration of electronic motion under the influence 
of a static magnetic field parallel to the axis of the 
cylindrical magnetron and of a radial electric field 
which is defined as a function of time and of an 
electron’s distance from the axis. Emission is lim- 
ited by space charge and the emitted electrons are 
initially assumed to rotate in circular orbits around 
the cathode. The analysis indicates that the circular 
orbit assumption breaks down when sufficient time 
elapses after the current ceases. This further indi- 
cates the possibility of transitory states during 
which electrons are constantly emitted from and 
returning to the cathode. No safe conclusion can be 


reached without adequate methods for their investi- 
gation. 

411-284 (A-9000, RP-461) (H. C. Early, H. W. 
AATlch) . Discusses the design and use of electro- 
magnets in circuits to provide self -regulating field 
excitation for c-w magnetrons. Because of conse- 
quent wide range of tuning with no adjustment of 
anode voltage, prevention of oscillation in a para- 
sitic mode, and easy regulation of power output, 
the method is useful in developmental and experi- 
mental work as well as in equipment used in the 
field. 


6 3 EFFECTIVENESS OF VARIOUS TYPES 
OF MODULATION 

411-TM-23 (A-3600, RP-197) (W. R. Rambo). 
Summarizes results of studies of the effectiveness 
of 7nechanical FM, electronic FM, and combina- 
tions of the two in high-power ground jamming of 
communication receivers in the 40-mc band. Modu- 
lation was by random noise and by a 120-c sweep 
signal supplied from a motor-driven rotating vari- 
able condenser. The scheme produced satisfactory 
jamming signals in the Fuge 16 receiver but was 
ineffective against a-m receivers equipped with 
noise limiters. 

411-2 (B-500, RP-207) (J. F. Byrne, R. J. 
Pierce) . Tests with laboratory equipment simulating 
a typical radar system using Type A presentation 
show that a jamming-to-signal power ratio of 34.0 
db is required for c-w jamming, of 17.5 db for 
modulated 100-kc sine-w^ave jamming, and 7.9 db 
for noise-modulated jamming (0-200 kc). The 
ratios become 60 db, 26 db, and 7.9 db, respectively, 
if the receiver be equipped with antijamming cir- 
cuits (described in detail). The conclusion is that 
noise modulation giving a signal at least 10 db 
higher than the reflected signal and containing fre- 
quencies above 200 kc is most effective in jamming. 
A receiver can be partially protected against jam- 
ming by means of an automatic biasing circuit and 
a 200-kc high-pass filter with switch to permit use 
only under jamming conditions. 

411-31 (B-500, RP-207) (R. J. Pierce). De- 
scribes and instructs in the use of an artificial radar 
system and jammer for measuring or demonstrating 
the effects of jamming under controllable condi- 
tions. The radar system produces simulated echoes 
which are variable in carrier frequency (100-350 
me) , amplitude (max r-f output varies between 3.0 
and 0.2 V with 96 db continuously variable attenua- 


430 


APPENDIX 


tion), length (1, 2, 5, 10, and 20 ^isec), range (2, 5, 
10, 15, 35, 70, and 150 miles), and azimuth (to 
simulate a moving target). It provides Type A 
and B presentation and has means for producing a 
main pulse and one echo, or two pulses of differing 
ranges. (See 411-22.) The jammer’s tuning range 
and output are the same as the radar’s. It may be 
modulated by sine wave (5-2,000 kc), noise (5- 
2,000 kc), or pulse (20-200 kc, 1-20 fxsec). (See 
411-14.) The report includes photos and circuit 
diagrams. 

411-55 (K-400, RP-186) (D. W. Taylor, D. A. 
Peterson). Summarizes observations of experimen- 
tal jamming of Type A presentations with sine- 
wave AM, noise AM, and direct noise. The results 
indicate that sine-wave AM is not effective, noise 
AM is effective (especially with close clipping) , and 
direct noise is effective (especially at high prf’s). 
Estimates of effectiveness are based upon the ratio 
of jamming power to signal power (J/S), assuming 
that the receiver is not overloaded and that the pips 
can be detected half the time. The report includes 
a description of the synthetic radar system and 
Dina jamming generator used in the investiga- 
tions. 

411-65 (K-400, RP-186) (D. W. Taylor, D. A. 
Peterson). Summarizes observations of experimen- 
tal jamming of Type A presentations with sine- 
wave FM, noise FM, and various combinations of 
AM and FM. Estimates are based on same assump- 
tions as used in 411-55. The results indicate that 
sine-wave FM is not effective and noise FM is 
effective (especially with clipped noise, large fre- 
quency deviation, and optimum bandwidth). Addi- 
tion of noise AM to sine-wave FM yields about the 
same effectiveness as did the best case of noise FM ; 
further addition of sinusoidal FM having proper 
frequency deviation enhances the effectiveness. The 
results from sine-wave FM plus noise FM were in- 
ferior. The report includes performance curves and 
sketches, with detailed comment on each case. It 
also includes a description of the f-m, a-m generator 
used in the investigations. 

411-71 (K-400, RP-186) (D. W. Taylor). Sum- 
marizes observations of experimental jamming of 
Type A presentations with AM, FM, and Dina 
when the receiver is overloaded. When the i-f am- 
plifier is overloaded, the jamming effectiveness of 
sine-wave AM and FM is increased but is still very 
inefficient, that of noise FM is first increased and 
then decreased, and that of Dina is increased. When 
the video amplifier is overloaded, the effectiveness 
of all these types of jamming is increased by an 
amount which is least in the case of Dina and great- 


est in the case of sine-wave AM and narrow-band 
clipped noise AM. The report includes performance 
curves and detailed comment about each case. 

411-75 (K-400, RP-186) (D. W. Taylor, J. M. 
Moran). Summarizes observations of experimental 
jamming of Type A presentations with constant- 
amplitude periodic and random pulses. The results 
indicate that periodic pulses are noneffective and 
that the effectiveness of random pulses increases 
with increase in the bandwidth of the noise which 
triggers the pulses. No significant change is caused 
by overloading the i-f or video amplifier provided 
that the bandwidth of the triggering noise is about 
five times that of the receiver. If it drops to two 
and one-half times greater, i-f overloading greatly 
decreases the jamming effectiveness and video over- 
loading slightly increases it. The report includes a 
description of the random-pulse generator employed 
in the investigations, showing a block diagram with 
tube complement and corresponding pulse shaping. 

411-80 (K-600, RP-186) (D. W. Taylor, J. M. 
Moran). Summarizes observations of experimental 
jamming of Type B presentations by means of 
Dina, sine-wave AM and FM, noise AM and FM, 
and periodic and random pulses when the i-f and 
video stages are not overloaded. All of these types 
of jamming are found to be much more effective 
against a normally loaded receiver in a B scope than 
in an A scope. The effectiveness for each case is 
given by detailed comment and curves with respect 
to such factors as antenna scanning rate, video gain, 
J/S ratio, modulation, etc. The report includes a 
description of a novel device for simulating antenna 
patterns. 

411-85 (K-600, RP-186) (D. W. Taylor). Sum- 
marizes observations of experimental jamming of 
Type B presentation when the i-f or video stages 
are overloaded. An increase in the degree of i-f 
overloading caused (1) a decrease in the effective- 
ness of jamming with noise AM and Dina, (2) a 
slight increase in the effectiveness of noise f-m jam- 
ming, (3) an increase in effectiveness of low-fre- 
quency sine-wave FM or AM, and (4) an increase 
in effectiveness of relatively high-frequency sine- 
wave f-m and a-m jamming. Except for relatively 
high-frequency sine-wave FM, an increase in video 
overloading caused an increase in the effectiveness 
of jamming in all cases. These results are applicable 
to the particular receiver employed in the tests; 
their relevance to other radar receivers can be de- 
termined only by similar studies with each receiver. 
The report includes an account of the test methods 
employed and plotted curves for the various re- 
ported results. 


RCM EQUIPMENT 


431 


411-248 (G-300 and 500, RP-103 and 217) 
(D. AV. Taylor). Summarizes the results of labora- 
tory studies of the effectiveness of jamming radar 
systems. Periodic jamming (sine-wave AM or FM 
and periodic pulses) is found to be completely in- 
effective against deflection-modulated scopes whose 
i-f or video stages are not overloaded. An intensity- 
modulated scope is susceptible to both periodic and 
random jamming. Random jamming, including 
noise AM or FM, random pulse, and Dina, is effec- 
tive against deflection-modulated scopes to a vary- 
ing degree. Effectiveness of noise AM is increased 
by increasing sideband power either by increasing 
percentage of modulation or by clipping (provided 
that the bandwidth of the clipped noise is about 
ten times that of the receiver) . Increase in clipping 
and in frequency deviation increases the effective- 
ness of f-m noise (provided that an optimum band- 
width is used). Random-pulse jamming is most 
effective when the upper frequency limit of the 
triggering noise is about five times the bandwidth 
of the receiver. 

411-238 (G-2700, RP-299) (D. Park) . Discusses 
an 8th Air Force appraisal of RCM based upon 
consideration of battle damage to aircraft. Analysis 
of the data with regard to Chaff leads to the esti- 
mate that the chances are about 70 to 30 in favor 
of a Chaff-protected squadron as compared to one 
on the same mission not so protected. No quantita- 
tive conclusions are possible with regard to elec- 
tronic jamming beyond a general indication that it 
interferes more with search and early engagement 
than with the direction of fire at any particular 
formation. 

411-7, 7A (F-1900, RP-305) (W. D. White). 
Analyzes energy distribution between carrier and 
sidebands for half-wave AM, full- wave AM, and 
FM carriers when each is modulated by random 
noise. It indicates that, for the same amount of 
radiated power in a noise signal, FM gives five 
times and half-wave AM gives three and one-half 
times the sideband energy given by full- wave AM. 
Similar analyses for suppressed carrier (balanced 
modulator) conclude that, while it is excellent in 
theory, it will have little practical value until suit- 
able u-h-f modulators can be built. 

411-29 (G-lOO, RP-181) (D. Middleton). Cal- 
culates the spectra resulting from various com- 
binations of AM and FM by noise. For barrage 
jamming, AM or FM by noise, superimposed on 
sinusoidal FM, should be more effective than AM 
or FM by noise alone. The introduction of sinu- 
soidal FM serves to spread the overall spectrum, 
thus increasing the barrage width without destroy- 


ing the uniformity of the jamming spectrijim. Four 
combinations of AM, FM, and sinusoidal FM are 
considered and found superior to sinusoidal FM 
alone. The results are based on considerations of 
relative spectral uniformity, spectral width, and the 
quality of the modulating noise, i.e., whether it is 
random or highly clipped. 

411-51 (G-103, RP-181) (J. H. Van Vleck). 
Calculates the spectra which result from clippmg 
an unmodulated noise band (Dina) and from a 
carrier modulated by clipped noise. It indicates 
practically no distortion in either if they are clipped 
at about 1.4 times the rms level after clipping. Even 
in cases of extreme clipping, spectral nonuniformity 
causes very little waste of power. Clipping is found 
to reduce peak power requirements and to lessen 
waste of power in the carrier frequency. Clipped 
noise is found to be fully as effective as undipped 
noise having the same spectral distribution provided 
the receiver width is small compared to the barrage 
width. 

411-86 (G-104, RP-181) (J. H. Van Vleck, 

D. Middleton). Presents a theoretical examination 
of the relative merits of visual, aural, and meter 
detection of radar signals in the presence of noise. 
The report consists of two parts: (1) a descriptive 
survey of results and (2) a mathematical discussion 
of the behavior of a superheterodyne receiver when 
a pulse-modulated carrier enters the device and is 
rectified in the presence of noise. Visual detection is 
considered in terms of the spreadout image pre- 
sented by an A scope, in which the criterion for 
signal detectability involves the ratio of peak signal 
to mean noise background. In aural or meter de- 
tection, where one listens to or measures the funda- 
mental or low harmonic of the prf, the important 
ratio is that of the signal energy in one particular 
harmonic component to the noise energy in the fre- 
quency region surrounding this component. The 
metering scheme may be either periodic (when the 
rectified current is passed by a narrow-band audio 
filter tuned to the prf and then rectified before being 
applied to the meter) or aperiodic (when the recti- 
fied current is fed directly to the meter and the d-c 
component takes the place of the harmonic com- 
ponent) . 

The sensitivity of any method depends upon the 
width and shape of the i-f response, the pulse 
length, and the prf. In aural or meter reception the 
duration of the gate (to reduce the noise back- 
ground by the fraction of time that the gate is 
open), the width of the audio filter, or the time 
constant of the meter, are also to be taken into 
consideration. Knowledge of the prf is not necessary 


432 


APPENDIX 


in the case of the aperiodic meter and the ear, which 
can discriminate frequency (equivalent to surround- 
ing the signal by a certain effective bandwidth) . All 
of these factors are discussed in detail, with par- 
ticular emphasis on the optimum i-f filter design to 
provide maximum signal-to-noise ratios. For both 
visual and aural detection this design is found to be 
expressed by a filter frequency characteristic which 
is the Fourier transform of the pulse. The best pulse 
for visual detection is the Fourier transform of the 
filter frequency response, whereas long pulses give 
the best results in audio or meter detection. The 
quadratic detector is appreciably better than the 
linear detector only for intense signals. By means of 
gating and long time constants (which tactical con- 
siderations may make difficult of accomplishment) , 
meter methods can potentially be made more sensi- 
tive than the A scope. 

411-86A (G-104, RP-181) (D. Middleton). Ex- 
amines the low-frequency output of a detector 
having an essentially half-wave quadratic response. 
This is considered as a particular case of a general 
theory of quadratic rectification of a modulated 
carrier in the presence of noise, which theory is also 
outlined. The powers of the transmitted 1-f noise 
and signal, and their spectral ordinates, are each 
shown to be one-quarter of their corresponding 
values for the full-wave quadratic detector. Conse- 
quently there is no change in the signal-to-noise 
ratios used in 411-86. The conclusions of the theory 
also remain unchanged, provided that attention be 
restricted to low frequencies and that the input 
noise band be narrow compared with the bandwidth 
of the i-f amplifier of the receiver. 

411-TM-41 (G-lOO, RP-81) (D. Middleton). 

Outlines a general theory for the rectification of a 
modulated carrier in the presence of noise (such as 
that from the i-f output stage of a receiver) and 
derives an equation for the (mean) envelope of the 
output wave from an unbiased linear rectifier. The 
general method is an extension of the theory devel- 
oped in 411-51. The equation is found to be equiva- 
lent to other previously derived special cases of this 
general noise theory. It was intended that this 
outline be the basis for attacking many specific 
noise problems. 

411-32 (G-200, RP-182) (J. H. Van Vleck). 
Investigates the efficiency of a series of pulses for 
barrage jamming. To cover barrages of the order 
10 me the pulses must be short, of the order 0.1 
psec or less. The pulses should be irregularly spaced, 
with a mean interval less than the characteristic 
time characteristic of the receiver bandwidth, i.e., 
less than a microsecond if this width is about 1 me. 


With such a pulse system the energy wasted in the 
carrier is small. 

411-TM-29 (G-200, RP-182) (J. H. Van Vleck). 
Mathematically analyzes jamming effect of slow 
jittered FM (wide-swing slow mechanical FM on 
which is superimposed a smaller swing noise FM) 
on phone reception of communications. The spec- 
trum at such a j amming signal consists of a discrete 
portion composed of harmonics of the mechanical 
FM and a continuous part. Since the energy of the 
discrete portion affects only certain nerves in the 
ear, its jamming effectiveness is very small as com- 
pared with that of the continuous portion. The best 
obtainable results of rapid, high-amplitude jittering 
put half the energy into the continuous portion. 

411-56 (G-300, RP-217) (D. Middleton, M. 
Steinberg) . Outlines the requirements, as suggested 
by theoretical considerations, for a possible use of 
various types of frequency modulation in conjunc- 
tion with AM or FM by noise to provide sufficiently 
wide and uniform barrages for the jamming of radar 
or communication systems. Frequency modulation 
by sinusoidal, unsymmetrical and symmetrical saw- 
tooth, and square waves is considered. Modulation 
with an unsymmetrical sawtooth wave, if prac- 
tically obtainable, is the most effective method for 
jamming either radar or communications systems. 
For radar, either sinusoidal or symmetrical saw- 
tooth wave modulation is also effective, while the 
symmetrical sawtooth wave may be used for com- 
munications. It is found that the sideband separa- 
tion should be not less than one-half the effective 
video or audio bandwidth of the receiver to be 
jammed and not greater than one-fifth the half 
barrage width. The spectrum is sufficiently uniform 
for barrage jamming of radar systems if half the 
barrage width is not less than 5 times or more than 
25 times the FM sweep frequency. The correspond- 
ing figures for jamming communications are 50 and 
3,000. The width of the noise band should be about 
three-fourths the sideband separation. 

411-TM-26 (G-301, RP-217) (T. S. Kuhn, L. 
Hoffman) . Studies the spectra due to simultaneous 
sine-wave AM and parasitic FM in a self-excited 
oscillator. The results are plotted to show spectral 
distribution (amplitude of first four sidebands 
relative to the carrier after modulation) as a func- 
tion of the modulation index {K — frequency 
deviation/modulating frequency) from K = 0 to 
K = 1.5 for phase differences of 0, 15, 45 and 90 
degrees between AM and FM. By estimating the 
value of K and the phase difference it is then pos- 
sible to judge the lack of symmetry in the spectrum, 
or vice versa. 


RCM EQUIPMENT 


433 


ANTENNAS 

NDC-rc-100 (Suppl. No. 1) (G. Sinclair). Dis- 
cusses methods for measuring aircraft antenna pat- 
terns by means of models and shows a number 
of representative three-dimensional patterns for 
mountings on various parts of aircraft. The shape 
of a pattern is found to be influenced by reflection, 
diffraction, and resonance in the structure of the 
aircraft. Knowledge of these factors makes it pos- 
sible to estimate radiation patterns for various 
antennas for many conditions. 

(August 31, 1942) 

NDC-rc-100 (Suppl. No. 2) (G. Sinclair). Pre- 
sents sample radiation patterns for antennas on 
aircraft and tanks and briefly discusses the meas- 
urement of antenna impedances by means of models. 
It is found that patterns for the horizontal and 
vertical planes are almost as useful as three- 
dimensional patterns and are much easier to obtain. 

(August 24, 1943) 

NDC-rc-100 (Suppl. No. 1) (G. Sinclair). De- 
scribes a method for determining tank antenna pat- 
terns by means of models. The lobes in the patterns 
for a model in free space are caused by reflections 
from the principal surfaces of the tank. Diffraction 
and resonance have little influence. Ground-reflected 
weaves affect only those antenna radiations at 15-20 
degrees above the horizon. 

(September 24, 1942) 

NDC-rc-100 (G. Sinclair, E. C. Jordan). Indi- 
cates the effects of airplane structure on polariza- 
tion of airborne antennas by means of patterns ob- 
tained from models. Examination of these patterns 
may aid in predicting the pattern for a proposed 
airborne antenna. 

(November 17, 1943) 

104-4 (77, RP-399-404) (G. Sinclair, W. Rife) . 
A final report on model measurements of antenna 
patterns and antenna impedance. Results at pattern 
measurements are satisfactory and have greatly 
aided in the design and development of all types of 
antennas. Preliminary impedance measurements in- 
dicated large errors around the antiresonant region 
of an antenna. Progress has been made in the con- 
struction of suitable standard impedances for cali- 
brating models. 

(October 30, 1945) 

411-100 (A. W. Alford). This comprehensive 
treatise catalogs 26 RRL production types of an- 
tennas and antenna systems for RCM in order to 
facilitate the proper choice, installation, and servic- 
ing of a given type for a desired purpose. For each 
type there is a detailed statement as to purpose. 


description, specification, impedance characteristics, 
radiation patterns, mountiiig location and instruc- 
tions, maintenance, and list of types having over- 
lapping frequency ranges. These detailed listings 
are prefaced by a brief discussion and explanation 
of such terms as antenna pattern, gain polarization, 
standing-wave ratio, and line-balance conversion 
units. Emphasis is placed on the need for taking 
both radiation pattern and standing-wave ratio into 
account when selecting an antenna for a given ap- 
plication. The chapter on installation includes a 
chart indicating possible antenna locations on an 
airplane. 

411-TM-22 (G-408, RP-107) (E. Fubini, P. J. 
Sutro) . Discusses the frequency characteristics of a 
bazooka, a particular type of transformer for feed- 
ing a balanced load from a single-ended line. Inser- 
tion of a pair of properly designed quarter-wave 
matching sections between the transformer and a 
load having a higher characteristic impedance is 
found to keep the standing-wave ratio below 1.25:1 
for frequency bands of the order of 4:1. Design 
parameters are given for matching a 50-ohm un- 
balanced line to 128-ohm and 150-ohm balanced 
line. 

Thick Stub, 70-400 me. 

Div. 15 RP-138 Army-Navy 

RRL M-313 AT-36APf (150-220 me) 

AT-37APT (113-150 me) 
AT-38APT (93-113 me) 
Slant Mount— AT-41 APT (150-220 me) 
Slant Mount— AT-42APT (113-150 me) 
Slant Mount— AT-43APT (93-113 me) 
Used with SCR-587, ARC-1, APR-1, 2, and 4 for 
vertical polarization. Consists of copper-plated, 
compregwood mast in rectangular mount. Copper 
area is connected to type N connector by tapered 
copper “dog-ear” whose shape and mounting are 
important factors in providing wdde-band feature. 

411-TM-92 (C. M. Daniell, M. J. White). Brief 
description, characteristics, photos, and graph of 
impedance versus frequency. 

411-153 (P. L. Harbury). Illustrated description 
of various types of stubs and mounts, discussion of 
theory of operation, and instructions for installa- 
tion, maintenance, and cabling. 

411-TM-93 (C. M. Daniell). Photos and charts 
of electrical characteristics for stub and cone assem- 
bly, 100-400 me, and 300-1,000 me. 

Div. 15 RP-138 Army AS-25/APR-2 

RRL M-801 Navy AS-25/APR-2 

Obsolete design for use with APR-2, replaced by 
M-313. Consists of a modified AN-104B stub for 
the lower-frequency range and a 60-degree cone 


434 


APPENDIX 


with a 90-degree cap for the higher-frequency 
range. 

411-TM-79 (H. C. Singleton). Description, 

sketches, photos, graph of impedance versus fre- 
quency of cone, 300-3,300 me. 

Div. 15 RP-138 Army AT-49/APR-4 

RRL M-2101 Navy AS-49/APR 

Used with SCR-587, ARC-1 for 290- to 1,650-mc 
range and with APR-1 and APR-4 for 300 to 3,000- 
mc range, mounted for either vertical or horizontal 
polarization. It consists of a 60-degree cone housed 
in a supporting nacelle. The pattern is nondirec- 
tional in a plane perpendicular to the axis of the 
antenna. 

Cone, 1,000-3,000 me. 

Div. 15 RP-138 Army AS-44/APR-5 

RRL A-2612 Navy AS-44/APR-5 

Used with APR-5 for vertical or horizontal po- 
larization. Pattern is nondirective perpendicular to 
axis of cone. Polarization depends upon mounting, 
whether vertical or horizontal. Structure includes 
700-mc high-pass filter, to minimize spurious re- 
sponses from lower frequencies. A-2602 is housed 
in a pressurized jacket, whereas A-2612 requires a 
blister. 

411-TM-77 (H. C. Singleton). Specifications, 
photo, and dimensional drawing for A-2602. 

411-TM-113 (P. L. Harbury). Modified specifica- 
tions, description, photo, assembly drawing, stand- 
ing-wave and impedance characteristics, and sug- 
gestions for installation. 

411-TM-113 (P. L. Harbury). Modified specifi- 
cations, description, photo, assembly drawing, 
standing-wave and impedance characteristics, and 
suggestions for installation of cone, 1,000-3,000 me. 
Div. 15 RP-138 Army AS-125/APR 

RRL A-2608 Navy AS-125/APR 

Used with APR-5 for vertical or horizontal po- 
larization. General features same as A-2612 ex- 
cept that cone is tilted 55 degrees to base plate 
and requires blister. Inclination of the axis mini- 
mizes null in direction of axis, thus providing 
fairly uniform radiation for horizontal polariza- 
tion when antenna is mounted on side of airplane. 

Waveguide, 3,000-6,000 me. 

Div. 15 RP-291 Army AS-45/APR-6 

RRL A-2701,R-1000 Navy AS-45/APR-6 

Used with APR-6. Installation comprises a wave- 
guide antenna and plastic hood (R-1004) and one 
of three optional types of wave-guide connections 


to the receiver (1x2 in.. Toll Ticket Tubing, or 
1^x3 in., whichever is more available or mechani- 
cally convenient). Condensation of moisture, with 
consequent high attenuation of signal, is prevented 
either by heating the system or by silica gel in a 
sealed system. The antenna pattern in the plane 
perpendicular to the broadside of the guide is ap- 
proximately a cardioid (equal gain over 180 degrees 
± 90 degrees from guide axis) and in plane perpen- 
dicular to narrow side of guide has equal response 
over 40 degrees ± 20 degrees from guide axis. Two 
sections (with a Y joint) may be used to feed a 
single receiver simultaneously from two antennas 
pointing to port and starboard. 

411-TM-71 (W. G. Wadey). Instructions for in- 
stallation of transmission lines, flanges, tapered and 
Y sections, and antennas, illustrated wuth sketches 
and photos. 

411-TM-88 (R-1012, RP-286) (W. G. Wadey). 
Description of a convenient type of fastener for 
quickly coupling two wave-guide sections. 

411-TM-80 (H. C. Singleton). Brief discussion of 
salient features, with photos, assembly sketch, and 
curves of standing-wave ratio of thick dipole, 75- 
300 me. 

Div. 15 RP-138 Navy AS-56/SPR-1 

RRL M-2408 

Used with SPR-1 for either vertical or horizontal 
polarization, depending upon mounting. Requires 
M-2406 conversion unit when used with unbalanced 
load. 

Double-cone Assembly, 225-1,000 me. 

Div. 15 RP-138 Navy AS-57/SPR-1 

RRL M-2409 

Used with SPR-1 for either vertical or horizontal 
polarization, depending upon mounting. It consists 
of two 60-degree cones supported by a cylindrical 
nacelle. Requires M-2410 conversion unit when used 
with unbalanced load. 

411-TM-81 (H. C. Singleton). Brief discussion of 
salient features, with photos, assembly sketch, and 
curves of standing-wave ratio. 

411-TM-55 (E. L. Bock) . Tests of the compara- 
tive performance of M-2409 and M-801 with semi- 
circular ground screen indicate that for some types 
of installation for vertical polarization M-2409 has 
a significantly greater response and for horizontal 
polarization, less directivity than has the M-801. 
The line length variation is greater in the case of 
M-2409. Various suggestions are given for using one 
of each type in order to provide adequate search 
coverage. The report includes photos, field patterns, 
and graphs of standing-wave ratios. 


RCM EQUIPMENT 


435 


411-IB-44. Illustrated description, preliminary 
instructions for installation, operation and main- 
tenance, and curve of standing-wave ratio versus 
frequency of antenna selection switch. 

Div. 15 RP-138 Navy SA-14/ APR-1 

RRL M-2404, -2413 SA-44/ APR-1 

411-IB-41. Antenna selection switch, frequencies 
up to 3.500 me. 

Div. 15 RP-138 Army SA-44A/APR 

RRL M-2415 Navy SA-44A/APR 

This six-position switch connects six or fewer 
pieces of equipment to one antenna or one piece of 
equipment to six or fewer antennas. When installed 
in a 50-ohm concentric line the switch introduces a 
standing-wave ratio of less than 1.5 to 1 for fre- 
quencies up to 3,500 me and of less than 3 to 1 for 
higher frequencies up to 5,000 me. Illustrated de- 
scription and instructions for installation, operation, 
and maintenance. 

TMR-48E. Minor changes in drawings to super- 
sede those in previous TMR’s. 

411-114 (RP-138, M-6301) (E. L. Bock, J. A. 
Nelson) . Brief illustrated description, graph of 
standing-wave ratio, and patterns of horizontal and 
vertical planes of balanced dipole and reflector 275- 
325 me. This antenna can be mounted at any point 
below the top of a mast. It consists of two modified 
M-1201 antennas fed in phase and mounted back to 
back on either side of the mast. Its pattern is sub- 
stantially circular in the horizontal plane. 


Skirted Stub, 275-325 me (RP-138, M-6302). 

This antenna is designed to be mounted at the top 
of a mast. It consists of a oyg-iri- stub fed against a 
9%-iu. skirt. Its pattern is circular in the horizontal 
plane. 

411-114 (E. L. Bock, J. A. Nelson). Brief illus- 
trated description, graph of standing-wave ratio, 
and patterns of horizontal and vertical planes. 

411-120 (J. A. Nelson). Describes the M-6302 as 
a vertically polarized antenna designed for vertical 
mounting on the rudder of a TBF airplane. The 
report includes performance curves for various 
mountings. 

TMR-252. Constructional data on M-4012 for 
250-500 me. 


TMR-253. 
500-935 me. 

TMR-254. 
90-147 me. 

TMR-255. 
88-175 me. 


Constructional 

data 

on 

M-4013 

for 

Constructional 

data 

on 

M-4015 

for 

Constructional 

data 

on 

M-4008 

for 


TMR-256. Constructional data on M-4011 for 
134-257 me. 

TMR-262, Report on vibration tests and voltage 
standing- wave ratio for M-4011. 

411-291 (RP-303) (J. Nelson, H. Horton, D. Wil- 
hoit) . Describes the various antennas in the M-4000 
series (81-203 me) , giving photos and performance 
curves. The report illustrates laboratory procedure 
in designing an antenna to meet certain speciflea- 
tions. These streamlined antennas are intended for 
low-speed patrol aircraft, such as PB4Y-2, at speed 
up to about 500 mph. They are tilt-mounted at 45 
degrees, with one for the same frequency range on 
each side of the plane. Each is fed by a separate 
transmitter to provide overlapping patterns with 
360-degree coverage. M-4003 has a range from 81 
to 111 me, M-4004 from 111 to 152 me, and M-4005 
from 144 to 203 me. 

411-TM-54 (C. M. Daniell). Brief description, 
characteristics, photos of two crossed, bent dipoles, 
505-580 me. 

Div. 15 RP-303 Army AS-69/APT 

RRL M-2202 Navy AS-69/APT 

Used with APT-2, APT-5, and APQ-1 for verti- 
cal, horizontal, and rotating polarization, and with 
APQ-9 for rotating polarization. It is so designed 
that the transmitted energy is directed primarily 
downward from the plane. The two dipoles are 
adapted for operation with a single transmitter by 
means of a quarter-wave phasing and matching sec- 
tion, and for operation with two transmitters by 
means of a pair of transformer sections which make 
the impedance of one dipole with a transformer 
equal to that for the combination used with a single 
transmitter. The assembly is housed in a Lucite 
dome outside the skin and in an iron box inside 
the skin. 

411-TM-53 (C. M. Daniell). Purpose, character- 
istics, photos, parts list, construction drawings, field 
pattern, and impedance graph of two crossed, bent 
dipoles, 520-580 me (RP-138, M-2201). Antenna 
resembles M-2202 except that it is not fitted with 
transformer sections for operation with two trans- 
mitters. 

411 -IB-33. Brief illustrated description of AI-2803 
and M-2804 with directions for installation of two 
stubs and balun, 150-210 me (RP-303, M-2804) . 
Used with APT-1 and AM-18/ APT for horizontal 
polarization. Assembly comprises two AT-36/APT, 
one M-2802 balun, . and two equal lengths of RG-9U 
cable. The balun maintains 180-degree electrical 
phase relation between the radiating elements. 

411-TM-122 (C. Driscoll). Brief description and 


436 


APPENDIX 


discussion; of installation, four field patterns, and a 
curve of standing-wave ratio versus frequency for 
bent, balanced-sleeve dipole, 195-295 me, 280-490 
me, 400-590 me. 

Div. 15 RP-303 Army AS-181/APT 

RRL M-3203 Navy AS-181/APT 

Consists of a permanently installed cylindrical 
mount (13 in. long) and three interchangeable an- 
tennas producing horizontally polarized radiation, 
distributed in a pear-shaped horizontal pattern with 
the principal lobe forward. Each antenna may be 
plugged into the mount and consists of a balanced- 
sleeve dipole bent into a Vee having an included 
angle of 100 degrees. 

Fishhook Antenna, 440-660 me. 

Div. 15 RP-303 Army AS-251/AP 

RRL M-2204 Navy AS-251/AP 

Designed for use with AN/APT-2 in all polariza- 
tions, this antenna has a single-lobed, circularly 
polarized field pattern approximately cosinusoidal 
in shape in all planes through the axis of the lobe. 
It consists of a pair of crossed-sleeve dipoles housed 
in a Lucite nacelle. The dipoles are fed approxi- 
mately 90 degrees out of phase by means of a 
phasing unit which is an integral part of the input. 

411-216 (J. Allen). Gives results of laboratory 
tests of 'performance of M-2204 when mounted in 
metallic recesses of various forms. The most satis- 
factory field patterns and circularity of polarization 
were obtained when the antenna system was 
mounted in a parabolic reflector 6% in. deep and 
36 in. in diameter. A Lucite cover for the recess does 
not substantially impair the results. 

411-298 (A. W. Alford). A summary report on 
fishhook antennas. 

411-IB-65, Preliminary instruction sheet giving 
electrical and physical characteristics, photos, 
curves of standing- wave ratio, and potential un- 
balance. 

Horn-Type Antenna, 2,310-4,000 me (RP-303, M- 
4902) . 

This circularly polarized antenna comprises (1) 
transformer consisting of a wave-guide section fed 
by the center conductor of a short coaxial cable 
from the transmitter, (2) polarizer consisting of a 
10 -cm length of wave guide shaped to resolve the 
exciting wave into two modes at right angles, (3) a 
phasing section consisting of a nearly square wave 
guide whose walls are at a 45-degree angle from 
those of the transformer and which is fitted to re- 
ceive a crystal detector and r-f filter unit whose 


output is fed to the indicating meter, and (4) a 
9%-in. diameter horn with a 130-degree flare. The 
antenna provides a substantially circularly polar- 
ized radiation, distributed essentially in a single- 
lobed, symmetrical pattern about 60 degrees wide 
between half-power points. When mounted against 
a ground plane, the radiator has a gain of about 
10 db over an isotropic radiator. 

411-IB-71. Illustrated description and explana- 
tion of theory of operation, preliminary instructions 
for installation, adjustment, operation, and main- 
tenance, field patterns, graph showing less than 3-db 
deviation from circularity of polarization through- 
out greater part of frequency range, and graph of 
standing-wave ratios. 

411-294 (P. Keeler). Gives preliminary design 
information and characteristics of M-4905, a modi- 
fication of M-4902 to provide circular polarization, 
for low-level bombing attacks against radar-pro- 
tected installations. In a partly successful attempt 
to accomplish this purpose, the phasing and flared 
sections of M-4902 were replaced by a sectoral horn 
to give a beam of the required shape. The report 
includes an account of the operation of M-4902 and 
M-4905 and a discussion of the parameters for de- 
termining the M-4905 characteristics, as shown by 
curves. 

Split Can Antenna, 575-1,400 me. 

Div. 15 RP-138 Army AS-180/APT 

RRL M-3301 Navy AS-180/APT 

Used for horizontal polarization in the 575- to 
1400-mc frequency range. The antenna consists of 
a grounded metal can in the shape of a truncated 
cone having a narrow slot along its full height. It 
is tuned to a desired 50- to 150-mc bandwidth in 
its frequency range by means of a variable shorting 
bar set to give less than 2:1 standing-wave ratio 
on a 50-ohm line. It is fed by a coaxial cable whose 
outer conductor is bonded the full length of the 
inner side of one edge of the slot, and whose inner 
conductor is tied to the other edge of the slot by 
a “dog-ear” which minimizes the inductive drop 
through this lead. The radiation is distributed pre- 
dominantly forward and to the sides of an aircraft. 

411-TM-34 (A. W. Alford, P. L. Harbury) . Gives 
results of preliminary experiments with radiation 
from split can antennas. 

411-IB-46. Brief description and operating in- 
structions, field patterns, and graph of shorting-bar 
position versus frequency. 

Slot Antennas (RP-303, M-6800) . 

Each of this series of faired-in, nonadjustable an- 


RCM EQUIPMENT 


437 


tennas for high-speed aircraft consists of a shallow 
box-like cavity which is energized by a T-shaped 
feeder. Each operates as a loaded stub in a short 
length of wave guide. Wide-band performance is 
obtained by the interaction of the reactances of the 
T joint, the shorted section of guide forming the 
back of the cavity, the aperture and skin forming 
the load. The aperture is covered with a thin sheet 
of Fiberglas. Input is made through a modified 
UG-lOl/U connector mounted in the side of the 
cavity and connected to the feeder through a tapered 
section of 50-ohm line. The radiation patterns are 
polarized perpendicularly to the long dimension of 
the slot, being wide in one plane and somewhat 
narrower in the other. 

411-166 (D. Lazarus). Describes the structure 
and characteristics of a slot antenna (M-6804) for 
the 1,050- to 2,100-mc range. 

411-263 (D. Lazarus). Summarizes preliminary 
development of wide-band slot antenna and dis- 
cusses operating theory and characteristics. Experi- 
mental installations in B-17 and PB4Y2 aircraft 
are described and transmitter radiation patterns are 
shown for various M-6800 transmitting antennas. 
Similar information is given for M-7300 curved slot 
antennas for XP4M airplane and S-1200 bomb-case 
jammer. The report is concluded with a brief ac- 
count of experiments with loaded slot antennas. 

411-TM-82 (H. C. Singleton). Brief Description, 
specifications, characteristics, sketch and photos 
of assembly, field patterns of dual dipole and re- 
flector, 90-150 me, ground-based. 

Div. 15 RP-279 Army AS-49/TPT-1 

RRL M-2508 Navy AS-49/TPT-1 

Used with APT-1, APT-3, AM-14/APT for verti- 
cal or horizontal polarization, depending upon ori- 
entation. Assembly consists of two dipoles fed in 
phase, each having a corner-type reflector and being 
adjustable in length to cover the frequency band. Its 
dimensions are approximately 6 x 11 x 4 ft, with 
weight of 208 lb. Employs M-2503 conversion unit 
to feed dipoles in phase and uses M-2504 trans- 
former unit to connect two assemblies in multiple. 

411-TM-83 (H. C. Singleton). Same as 411-TM- 
82 except as regards modifications for higher- 
frequency range. Dual dipole and reflector, 150- 
210 me, ground-based. 

Div. 15 RP-279 Army AS-50/TPT-1 

RRL M-2511 Navy AS-50/TPT-1 

Used with APT-1, AM-18, APT. Equipment is 
similar to M-2508, except as modified to cover 
higher-frequency range. Employs M-2509 conver- 
sion unit to feed dipoles in phase and M-2510 trans- 


former unit to connect two assemblies in multiple. 
Uses same connecting cables as M-2508. 

411-IB-70. Illustrated description and prelimi- 
nary instructions for installation, adjustment, oper- 
ation, and maintenance, with field patterns and 
graph of standing-wave ratio of dipole and corner 
reflector, 460-720 me. 

Div. 15 RP-138 Navy AS-71/SPT-2 

RRL F-3701 

Used with APT-2, APT-5, APQ-9, UPT-Tl. The 
range is covered by adjusting the lengths of the 
dipole arms for the desired frequency. The entire 
band can be covered in five settings. Adjustable 
members are protected from the weather by a 
waterproof sleeve. Antenna can be used with an 
input power up to 75 w and has a gain of about 
10 db in the maximum direction. Polarization is in 
the direction of the axis of the dihedral angle and is 
adjustable by rotating the antenna and reflector 
assembly. 

TMR-57. Brief discussion, chart of dipole length 
versus frequency, parts list, constructional draw- 
ings. 

TMR-57A. Drawings for protective sleeve and 
information on dipole adjustment. 

411-TM-78 (H. C. Singleton). Discussion of 
salient features, field patterns, chart of dipole length 
versus frequency, drawing and photo of assembly of 
dipole and corner reflector, 175-550 me. 

Div. 15 RP-138 Army AS-263/UPT 

RRL F-3903 Navy AS-263/UPT 

Used with APQ-2. The operation depends upon 
the adjustments of the length of the dipole in the 
corner reflector. Several settings of each of these 
parameters are necessary to cover the frequency 
range with a standing- wave ratio of less than 2:1. 
The field pattern is . practically independent of po- 
larization. The antenna gain is approximately 10 db. 

TMR-92. Brief description, parts list, photo, con- 
structional drawings for F-3903. 

TMR-92A. Brief description, photo, parts list, 
and construction drawings for F-3903 ship-borne 
directional antenna system designed primarily for 
use with F-3800 practice jammer. 

411 -IB-58. Illustrated description and prelimi- 
nary instructions for installation, adjustment, op- 
eration, and maintenance, including antenna pat- 
terns and graph of standing-wave ratio versus fre- 
quency of dipole and corner reflector, 700-1,300 me. 

Div. 15 RP-138 Navy AS-145/SPT-6 

RRL F-3702 

Used with SPT-6 and APT-5. Consists of an ad- 


438 


APPENDIX 


justable dipole, provided with a balanced matching 
section, mounted in a corner reflector. An adjustable 
mounting bracket and calibrated scale permit set- 
ting the antenna and reflector assembly at any 
desired orientation in a single plane. The frequency 
range is covered in three settings of dipole length. 


End-Fed Balanced Antennas, 85-800 me. 


Div. 15 RP-138 

Navy CAKZ-66AJA 

RRL M-2901 

CAKZ-66 AJB 

M-2902 

CAKZ-66 AJM 

M-2903 

CAKZ-66 AKJ 

M-2904 

CAKZ-66 AKL 

M-2906 

CAKZ-66 AKM 

M-2907 

CAKZ-66 AJY 

M-2908 

CAKZ-66 AJR 

M-2909 

CAKZ-66 AJY 

M-2910 

M-2912 

M-2913 

These antennas are designed for use with CXFR, 


TDY, or SPT-7 transmitters without adjusting the 
antenna throughout its rated range. M-2901 covers 
the 350-685 me range, M-2902 the 645-800 me 
range, M-2903 the 175-350 me range, M-2904 the 
85-175 me range, M-2906 the 143-275 me range, 
M-2907 the 265-540 me range, M-2908 the 450-820 
me range, M-2909 the 800-1,400 me range, M-2910 
the 810-1,385 me range with TDY, M-2913 the 810- 
1,385 with the SPT-7 transmitter. All are designed 
for waterproof mounting on a mast. Each consists 
of a dipole, untuned reflector, and converter from 
unbalanced to balanced transmission line. The pat- 
terns for vertical polarization in the horizontal 
plane are broad enough to allow for changes in the 
ship’s course with small reduction in signal toward 
the target. The patterns for vertical polarization 
in the vertical plane are w\de enough to allow for 
moderate roll of the ship and yet^ narrow enough 
to prevent undue waste of energy at angles removed 
from the horizontal. 

411-TM-140 (E. L. Bock). Illustrated descrip- 
tion of M-2903 with graphs of standing- wave ratio 
versus frequency and field patterns for various re- 
flector spacings. 

411-218 (G. Stavis). Describes the mechanical 
construction and the electrical performance of the 
M-2914 r-f relay for remote switching of antennas. 
The report includes voltage standing-wave ratio 
curves showing effects of two types of right-angle 
connectors on the electrical performance of the 
relay. 

411-210 (E. L. Bock). Gives design information 
and dimensions for building M-2900 corner-type 


antennas covering 140- to 1,400-mc range by means 
of four antennas. Each is fundamentally a sleeve 
dipole in a 135-degree corner reflector. Sleeve and 
balun impedances are given along with typical 
curves of standing-wave ratios and measured field 
patterns. 

411-TM-134 (C. Driscoll). Description, photos, 
measured field patterns and graphs of energy dis- 
tribution and standing-wave ratio under various 
experimental conditions of high-gain antenna, 
1,500-3,000 me (RP-138, M-4400). This laboratory 
model typifies a suitable ground-based antenna to 
be used with a jammer operating above 1,500 me. 
The model produces vertically polarized radiation 
in a 30-degree fan-shaped pattern in the horizontal 
plane and 6 degrees in the vertical plane. It gives a 
gain of 23.4 db at 1,500 me and 27.7 db at 3,300 me. 
The antenna consists of an 8-ft cylindrical para- 
bolic reflector fed by a 3-ft horn. A similar antenna 
with a height of 5 ft or less may be adapted for 
ship-borne use in the 10-cm region. 

411-TM-143 (W. G. Wadey). Brief description 
illustrated by sketches, with statement of pattern 
characteristics of search antennas, 3,000-6,000 me. 

Div. 15 RP-107 

RRL R-1004 
R-1022 

Used with AN/APR-5A receiver aboard naval 
vessels for searching in the 5- to 10-cm range. 
R-1022 is a biconical horn feeding a separate coaxial 
cylindrical line joined to a wave guide by a con- 
tinuous transformer; it is used for reception of verti- 
cally polarized weaves. R-1004 consists of the open 
end of a toll ticket tubing wave guide covered with 
a hood to keep out the weather; it is used for hori- 
zontal polarization. Each has a broad pattern in the 
horizontal plane with a single null, the desired form, 
since the antenna will be installed on either the 
forward or aft side of the mast at or below the level 
of the yardarm. 

411-101 (C. Driscoll). Illustrated description, 
suggestions for installation and operation, field pat- 
terns, and graph of standing-wave ratio of high- 
gain antenna, 2,880-3,310 me (RP-303, M-4701). 
This horizontally polarized antenna was used to 
test the jamming effectiveness of a klystron tube 
transmitter having 10-w output (Q-llOO). It has a 
gain of about 23 db and its sharp radiation patterns 
are suitable for screening a destroyer at 5,000 yd 
against a microwave medium-power radar system. 
It consists of a horn-fed cylindrical parabolic re- 
flector with a swivel base permitting 360-degree 
rotation and about 20-degree variation in elevation. 
The horn is fed by a wave guide which is fed by a 


RCM EQUIPMENT 


439 


length of RG-14/U cable from the transmitter. A 
matching adjustment between the cable and guide 
is provided by a movable plunger at the end of the 
wave guide. A pair of sights attached to the reflector 
and aligned with the axis of the radiation pattern 
provides accurate sighting control of the radiation 
direction of a visible target. 

411-18 (J-400, RP-107) (R. Silliman). Gives 
results of measuring the input impedance versus 
frequency characteristics of various models of cone 
antennas. The data are presented by curves plotted 
in terms of driving-point impedance versus overall 
length in wavelengths. Curves are also plotted for 
the coefficient of reflection and standing-wave ratio 
(see 411-23) of one of the models. The general con- 
clusions are that the bandwidth of a cone antenna 
depends upon the allowable degree of terminal mis- 
match, being less for transmitting than for receiv- 
ing. For a 0.17 reflection coefficient {R) a bandwidth 
of 3 to 1 is obtainable from a 70-ohm line or 1.5 to 
1 from a 50-ohm line. A bandwidth of at least 4 to 1 
is obtainable from either type of line for R = 0.33. 

411-34 (MJ-2100, RP-107) (C. M. Daniell). 
Gives results of measurements of impedance char- 
acteristics of cylindrical antennas varying from 10 
to 256 in ratio of length to diameter and from 
% to 1 wavelength in length. The data are presented 
in the form of curves from which it is concluded 
that the effect of decreasing the ratio of length to 
diameter is to smooth the resistance and reactance 
curves, with relatively small effect on the resistance 
at the quarter-wave and three-quarter-wave reso- 
nance points and large effect at half-wave and full- 
wave resonance. The divergence between the elec- 
trical and physical lengths is found to increase more 
rapidly for long than for short antennas and for 
ratios of length to diameter of less than 30 to 1. 

411-TM-34 (M-2700, RP-303) (A. Alford, P. L. 
Harbury). Reports on preliminary experiments on 
radiation from split can antennas. The antennas 
were metal cylinders (30 cm long and of various 
diameters) split lengthwise along one side. When 
one end of the antenna is connected to the ground 
plane it is energized by a single coaxial line con- 
nected either to the top or the center of the can. 
When the antenna is raised above the ground plane 
by small insulators it is energized by a balanced 
feed (conversion unit) connected to the bottom of 
the can. Test results tend to substantiate the tenta- 
tive theory that the two edges of the lengthwise 
split constitute the two wires of a transmission line, 
whilst the effect of the rest of the can represents 
that of a number of loops shunted across the lines. 
Because most of the energy is radiated from these 


“loops,” the radiation is polarized in a plane per- 
pendicular to the lengthwise axis of the can. An 
antenna can be energized to give either vertical, 
horizontal, or circular polarization. AVhen the shunts 
are in length, the resonant frequency is deter- 
mined solely by the length of the can. 

411-23 (G-400 and J-302, RP-107 and -138) 
(E. Fubine, P. J. Sutro, R. F. Lewis). Gives meth- 
ods for calculating the characteristics and perform- 
ance of wideband matching line sections in series at 
frequencies other than those for which they were 
designed. The sections investigated include single 
and double quarter-wave (which are found to cover 
very much wider bands than are usually assumed) 
and half-wave sections (for matching a load at two 
frequencies) . The concept of “ideal load” is intro- 
duced — that is, the load which varies with fre- 
quency in such a way as to compensate exactly for 
the frequency characteristic of the transformer. 
Thus the matching problem is reduced to that of 
finding the matching transformer whose ideal load 
most nearly approximates the actual load to be 
matched. In terms of this concept, the case of a 
transformer composed of a single section of line is 
considered in detail, and plots of ideal load as a 
function of frequency are included. A simple formula 
is given for the reflection coefficient in terms of the 
ideal and actual loads. An appendix discusses the 
factors which limit the acceptable mismatch in 
transmitting and receiving antennas. 

411-TM-24 (G-1000, RP-107) (Donald Foster). 
Explains and proves the validity of a method for 
calculating the pattern of an antenna. The method 
is based upon choosing as an origin of radiation 
some point, if it exists, at which the equivalent 
current phase is independent of direction, and re- 
garding the entire antenna as an array of such spe- 
cially located point radiators. The Poynting flux is 
then readily calculated from the magnetic vector 
potential. Examples are given for a dipole consist- 
ing either of straight nonresonant elements or of 
segments one-quarter wave in length. 

411-TM-42 (G-1000, RP-107) (Donald Foster). 
Describes an airborne lobe-switching antenna to 
locate enemy transmitters of unknown frequency. 
The antenna consists of a small horizontal Vee 
mounted with its open end toward a vertical reflect- 
ing plate. The pattern usually has one lobe pointed 
backward toward the driving point. The lobe is 
switched to either side of a vertical plane normal to 
the reflecting plate by interchanging the driving 
point and the terminating resistance. Satisfactory 
lobe-switching patterns are obtained for two ranges 
of the ratio of a side of the Vee to the wavelength. 


440 


APPENDIX 


These ranges are approximately 0.4 to 0.6 (for 
which the radiation resistance is nearly constant at 
90 ohms) and 0.12 to 0.35 (for which the radiation 
resistance varies from 5 to 72 ohms as a linear func- 
tion of the frequency) . The report contains a num- 
ber of directional patterns calculated by a formula 
which is illustrated by a sketch. 

411-TM-123 (G-1000, RP-107) (Donald Foster) . 
Gives general equations describing the salient fea- 
tures of loop antennas in the shape of a circle or of 
large polygons having a center of symmetry. Con- 
sideration is given to unattenuated traveling cur- 
rent waves, standing waves, and uniform current 
distributions. Various ways are shown for driving 
polygons or circles with substantially uniform cur- 
rent. It is suggested that similar directivity patterns 
and polarization characteristics might also be ob- 
tained by means of wave guides terminated by an- 
nular horns. The solution of the problem of the 
circular antenna wdth uniform current is treated in 
detail, giving directivity and radiation-resistance 
graphs. With uniform current and less than two 
wavelengths in the perimeter, the circle or polygon 
seems to have possibilities as a transmitting an- 
tenna for horizontally polarized waves. At high fre- 
quencies or with large loops the vertically mounted 
circular antenna may be used to transmit in a par- 
ticular direction with either horizontal or vertical 
polarization, depending upon whether the normal 
to the loop lies in the same vertical plane or the 
same horizontal plane as the target. Rotation of the 
normal to the circle around the direction of the 
target would rotate the direction of polarization 
around the ray at the same speed. 

411-192 (G-1000, RP-107) (D. Foster). Theo- 
retically determines an optimum directivity pattern 
for search antennas. The determination is based 
upon permitting the maximum area to be inspected 
per unit time of search with uniform quality and 
upon the probability of detecting the presence of an 
operating radar in that area. The resulting pattern 
has (1) a forward bulge which is sufficient to detect 
operating radar close to the line of flight and (2) a 
forward slanting region having a constant minimum 
transit time. 

411-158 (G-608, RP-318) (D. Foster). Describes 
and analyses two methods for locating a rotating 
beam transmitter by means of continuously rotating 
DF antennas with azimuthal scope presentation. 
Either method overcomes the difficulty caused by 
the false-direction indication due to variation of 
field strength of the receiver. One method merely 
requires the selection of the largest of a number of 
curves (eight are typical) drawn on the scope by 


a single receiving antenna having a much higher 
rotational speed than the transmitter. The other 
method requires two DF antennas having mirror- 
image directivity diagrams and rotating at the same 
speed in opposite directions. True direction is then 
found by bisecting the angle between the two false 
directions that are indicated when the antennas are 
so adjusted in relative angle that their outputs trace 
identical curves on the scope. 

411-119 (A. W. Alford, I. G. Clarke). Presents 
five semiempirical equations for determining the 
power gain and beamwidth of high-gain antennas. 
The formulas for gain are in terms of known 
(1) aperture and operating wavelength, (2) beam- 
widths, and (3) number of half-wave radiators in 
a mattress array. The formulas for beamwidth are 
in terms of known aperture dimensions and wave- 
lengths. Eight numerical examples are given for 
comparison with measured values. 

411-212 (M-1037, RP-306) (D. Lazarus). In- 
structs on methods for adapting AS-161/ART and 
AS-97/ART whip antennas as radiators horizon- 
tally polarized in the 75-mc region. Two whips are 
cut to 40-in. lengths, bent at a 45-degree angle, and 
installed (properly phased) on opposite sides of the 
fuselage toward the forward end of a plane. They 
may also be easily modified for pressurization, if 
necessary. The report includes test procedure and 
data which indicate the required broad patterns 
with maximum radiation forward and below the 
aircraft. 

411-203 (M-7501, RP-481) (J. Margolin) De- 
scribes field modifications of AN -1^8 A (designed 
for IFF) to adapt it for interim use as an anti-GL 
antenna in the 200-mc region. The report includes 
structural sketches and standing-wave measure- 
ments. 

411-203A (W-2210, RP-481) (M. P. Klein). 
Gives results of flight tests for determining the 
radiation characteristics of modified AN-I 48 A an- 
tenna. The characteristics appear to be satisfactory 
for use in jamming horizontally polarized GL radars 
in 200-mc region. 

411-202 (M-7407, RP-299) (H. Clark and E. F. 
Shaw). Presents 59 graphs to be used in determin- 
ing optimum height of jamming antennas. In most 
of the graphs the field strength in volts per meter 
is plotted against the range of the enemy ship in 
yards. Calculations are based on jammer heights of 
40, 80, and 120 ft and on enemy radar heights of 
80 and 120 ft at frequencies from 200 to 6,000 me 
with both vertical and horizontal polarizations. 
Values chosen for jammer power, antenna power 
gain, and cable or wave-guide attenuation are given 


RCM EQUIPMENT 


441 


on: each graph. Methods of calculation are explained 
in the report. 

411-242 (C-3303, RP-481) (J. W. Christensen). 
Describes the rapid method and simple equipment 
used to obtain continuous antenna patterns from 
small-scale models of whip antennas mounted at 
different positions on a rotating model of a B-24. 
Patterns are obtained by photographing polar traces 
on a plan-position indicator scope having radial 
deflection and long-persistent screen. Selsyns syn- 
chronize the scope’s rotational deflection with rota- 
tion of the model. The drive mechanism and indi- 
cator consist of modified DMB equipment. The 
method’s usefulness is illustrated by conclusions 
drawn from studying the effects of bending antennas 
that are usually mounted perpendicularly, thereby 
minimizing nulls. 

411-283 (C-3200, -3500, RP-303) (C. C. Loomis, 
R. M. Hatch). Describes methods and equipment 
used in designing two circularly polarized 8-band 
antennas for shipboard use. Each was to have a 30- 
degree elevation pattern centered on the horizontal 
(to allow for =b 15-degree roll or pitch) , one with a 
360-degree azimuth pattern and the other with a 90- 
degree pattern. Since the antennas were to utilize 
an M-9001 horn, the problems were reduced to de- 
signing proper reflectors. These problems and their 
compromise solution are discussed in detail. An- 
tennas which meet the specifications in some im- 
portant respects are described. 

759-1 (G. Sinclair) Gives patterns of cone an- 
tenna models of various sizes mounted on a circular 
plate. These measurements are preliminary to the 
measurements for cones mounted on aircraft and 
show various distortions which are briefly discussed. 

(October 29, 1942) 

759-2 (G. Sinclair). Gives radiation patterns of 
a cone antenna at two locations on a B-17E. Most 
of the energy is found to be vertically polarized and 
there is no evidence of pronounced structural reso- 
nances in the aircraft. 

(November 22, 1942) 

759-3 (G. Sinclair) . Gives patterns of cone an- 
tennas on a B-24 and suggests optimum locations 
for 100- to 300-mc and 300- to 1,000-mc antennas 
to be used for reception of signals of unknown 
polarization. 

(December 20, 1942) 

759-4 (G. Sinclair). Gives patterns of a dipole 
on AT -11 aircraft at 110 me for three mounting 
locations. 

(December 28, 1942) 

759-5 (G. Sinclair). Gives patterns of horizontal 


stub antennas projecting from the nose ot an AT-11. 
Measurements simulating 200 me were made for a 
quarter- wave stub, a three-quarter stub, and a 
quarter-wave stub with disk. 

(January 21, 1943) 

759-6 (G. Sinclair). Gives patterns for 50-ohm 
cone mounted on a disk for simulated operation at 
250, 400, and 1,000 me. 

(January 23, 1940) 

759-7 (G. Sinclair). Gives patterns of an array 
for SCR-587 on B-17F. The report tells how the 
array is phased. 

(February 20, 1943) 

759-8 (G. Sinclair). Gives patterns of stub an- 
tenna pairs for RC-164 lobe switching on B-17F at 
115-130 me. 

(March 17, 1943) 

759-9 (G. Sinclair). Briefly discusses patterns of 
antennas for Gyinnast, including those given in 
759-7 and 759-8, and predictions of those for vari- 
ous search receivers in 75- to 1,000-mc range. 

(March 25, 1943) 

759-10 and 759-11 (G. Sinclair, R. B. Jaques) . 
Gives patterns for antennas mounted on Hairy But- 
terfly. The antennas are dipoles and loops of various 
sizes mounted at various locations. 

(May 15, 1943) (June 11, 1943) (June 25, 1943) 

759-12 (R. B. Jaques) . Gives antenna patterns of 
special loop on A-29 bomber for 200 me. 

(July 24, 1943) 

759-13 (R. B. Jaques) . Gives patterns of vertical 
antennas on B-17 and B-24 bombers for 35 me. 

(August 2, 1943) 

759-14 (R. B. Jaques). Gives patterns of a short, 
wide-band antenna for 200- to 500-mc range. 

(August 2, 1943) 

759-20 (RP-137) (^. A. Jones, G. Sinclair). Pre- 
sents antenna radiation patterns for Albatross I 
project. Measurements were made on M-1203, 
M-801, and a quarter-wave stub installed on the 
equivalent of a PB4Y-2. 

(February 25, 1944) 

759-21 (RP-269) (R. B. Jaques). Presents re- 
flection patterns of B-24 100 me, based on data 

taken on a scale model of the bomber. 

(March 18, 1944) 

759-22 (RP-269) (R. B. Jaques). Presents re- 
flection patterns of B-17E at 100 me, based on data 
taken on a scale model of the bomber. 

(March 18, 1944) 

759-23 (RP-137) (E. A. Jones). Presents an- 
tenna radiation patterns for H 8-293. 

(June 20, 1944) 


442 


APPENDIX 


759-24 ^E. W. Vaughan, N. Kennedy). Gives 
constructional data for a square root amplifier de- 
signed to drive a square-law recording indicator so 
that the deflection of the pen is proportional to the 
square root of the amplifier input voltage. 

(May 29, 1944) 

759-26 (RP-137) (E. A. Jones). Presents radia- 
tion patterns for antennas on PBJfY-2, including 
M-1203, M-801, stub mast, IFF whip, and v-h-f 
whip. The models were 1/10 and 1/20 scale. 

(September 10, 1945) 

759-27 (RP-137) (E. A. Jones). Presents radia- 
tion patterns for antennas on P4M, including AT- 
49/ APR-4 and AN/APX-8. 

(September 1, 1945) 

759-28 (RP-137) (E. A. Jones). Presents radia- 
tion patterns of antennas on Ferret C-1 project, 
including an AT-43/APT stub and two AS-97/ART 
stubs fed as a two-wire fan and a three-wire fan. 

(September 10, 1945) 

759-29 (RP-137) (E. A. Jones) . Presents antenna 
radiation patterns for 1,000 me on the SB 28. The 
AS-133/APX-6 was mounted at three locations in 
an effort to determine the best location. A pattern 
calculated by rap-optics theory has the same num- 
ber of lobes as the model pattern, but the lobes have 
different angular positions. 

(September 13, 1945) 

759-30 (RP-269) (K. P. Yates, P. C. Wright). 
Describes experimental procedures used and gives 
the results obtained for reflection measurements on 
target tow cable designed at RRL to be antiresonant 
at 10- to 11-cm wavelengths. Using data obtained 
from tentatively designed samples, an improved 
antireflective cable was designed, tested, and found 
to give good performance. 

(August 13, 1945) 

759-31 (RP-137) (D. R. Rhodes, E. C. Jordan). 
Discusses the modeling of slot antennas for the 
measurement of patterns. Preliminary investigation 
of calculated and measured patterns indicate that 
the patterns of slot antennas are as predictable as 
those of any of the more common types. 

(October 3, 1945) 

759-32 (RP-427) (H. Heil, E. Jordan, D. Cleck- 
ner) . Discusses the modeling of ship-borne antennas 
for the measurement of patterns, taking into ac- 
count the effect of the sea on the pattern. Compari- 
son of theoretical curves with experimental data 
indicates that the pattern is a function of distance, 
that the total unattenuated pattern closely re- 
sembles that given by a model over a highly con- 
ducting ground screen, and that the fields of a dipole 


account for the effect of finite conductivity upon 
the pattern at any particular distance. Patterns 
obtained with a model sleeve antenna for 18 me 
showed reasonable correlation with measurements 
on the prototype. A terminated ground plane of rea- 
sonable size is found to be satisfactory for measur- 
ing patterns using wavelengths less than 50 cm. 

(October 16, 1945) 

759-33 (RP-269) (K. P. Yates, P. H. Nelson). 
Describes a c-w method for measuring reflection 
patterns from scale models of aircraft, RCM decoys, 
missiles, and other bodies by means of a trans- 
mitting and receiving system which discriminates 
between the transmitted and reflected signals. The 
measuring system is essentially a directional an- 
tenna array mounted within a wave guide with 
horn so that the array rejects energy transmitted 
through the guide toward the model and absorbs the 
signal reflected from the model. The method de- 
pends upon the principle of electromagnetic simili- 
tude whereby the reflection of 2,000-mc energy from 
a l/20th scale model, for example, is equivalent to 
that of 100-mc energy from the prototype. The 
report contains sample patterns which partly dupli- 
cate those listed herewith for specified measure- 
ments of reflections from bombers, corner reflectors, 
and tow cables. The report also describes the use of 
models in studying radar echoes from mortar shells 
and rockets. 

(October 18, 1945) 

759-34 (RP-137, -269, -427) (G. Sinclair). Sum- 
marizes Ohio State University research for Division 
15 of the Office of Scientific Research and Develop- 
ment, including work done on communications jam- 
ming equipment, airborne and ship-borne antenna 
radiation patterns, and aircraft echoing areas. 

(October 16, 1945) 

778-5 (S. A. Schelkunoff, W. C. Babcock) . De- 
scribes a proposed broad-band airborne antenna 
system and a method for broadening the band of an 
antenna by means of equalizing circuits. The pro- 
posed system consists of two parallel spaced wires 
(one insulated and the other grounded) running 
from tail to wing tips and fed by a transmission 
line running back to the tail. Analysis shows that 
they should provide a practical antenna for barrage 
jamming at lower frequencies. The band-broadening 
method is illustrated by the design of networks to 
use with two whip antennas over the 38- to 48-mc 
band. 

(January 26, 1943) 

867-1 (RP-261) (R. Serrell). Correlates work 
done at CBS and Ohio State University Research 
Foundation on design of a suitable antenna system 


RCM EQUIPMENT 


443 


for Moth. Preliminary measurements at 122 me in- 
dicate that approximately the same power is de- 
livered by a loop and half-wave dipole. The report 
includes drawings and radiation patterns for two 
proposed dipoles with horizontal polarization and 
one with vertical polarization. 

(November 1943) 

867-5 (RP-261) (J. A. Nelson). Gives graphs 
showing the input impedance of long-wire antennas 
having a cylindrical cross section. The general con- 
clusions are that the antennas are predominantly 
capacitive with a mean reactance of about 30 ohms 
and that the variations in resistance and reactance 
become smaller as the electrical length of the an- 
tenna increases and as the physical length-diameter 
ratio decreases. Measurements were made for elec- 
trical lengths varying from one-half wavelength at 
100 me to five wavelengths at 1,000 me. 

(January 14, 1944) 

867-7 (RP-261) (R. Serrell). Describes stub an- 
tennas with series matching sections suitable for 
mounting on the B-24 and for covering the 34- to 
38-mc, 38- to 42-mc, and 42- to 50-mc bands with 
a standing-wave ratio in a 50-ohm feed line not 
smaller than 0.5. 

(April 1944) 

867-10 (RP-261B) (E. C. Hayden). Describes 
an electromagnetic model of the ocean to be used in 
obtaining patterns of antennas mounted on ship 
models. The ocean surface is represented by a large 
bronze screen surrounded by “Uskon cloth” absorb- 
ing screens to prevent reflections at the boundaries 
of the model. Test measurements of patterns indi- 
cate that the model is satisfactory for most meas- 
urements. 

(February 1945) 

895-1 (RP-260) (P. S. Carter) . Gives the meas- 
ured impedance characteristics and radiation pat- 
tern of a sleeve antenna consisting of the outer sur- 
face of a coaxial line and the projection of the inner 
conductor. The impedance characteristic is found to 
be somewhat broader than that of a dipole. The 
resonant resistance is about 100 ohms. A frequency 
band of one octave can be covered with less than 
50 per cent reflection. The report also states that 
the use of steel for antenna units does not intro- 
duce appreciable losses compared with the use of 
copper. 

(July 14, 1943) 

859-2 (RP-260) (R. S. Wehner). Tells of im- 
proved impedance characteristics resulting from 
using the sleeve antenna principle with a corner re- 
flector, a fan, and an inverted L. Use in a corner 


reflector yields good directivity combined with 
bandwidths ranging from 10 per cent at 5 per cent 
reflection to 50 per cent at 30 per cent reflection. 

(September 9, 1943) 

859-3 (RP-260) (P. S. Carter). Gives an ap- 
proximate formula for estimating the power limit of 
airplane antennas and gives a curve sheet of values 
for quarter-wave antennas at 40,000-ft altitude in 
rainy weather. The values for a free-space dipole 
are about twice those shown by the curve and are 
greatly reduced as the length of the antenna is re- 
duced below one-quarter wavelength, being propor- 
tional to the radiation resistance for a particular 
length. 

(August 12, 1943) 

895-10 (RP-260) (P. S. Carter, R. S. Wehner). 
Gives results of antenna tests and flnds that a sleeve 
antenna is useful over a wider band than is a helical 
antenna, dielectric cone, dielectric cylinder, or half 
folded dipole. A quarter-wave stub mounted on a 
B-24 matches a 50-ohm line at 40 me, is good for a 
band of several megacycles, and distributes radia- 
tion satisfactorily. 

(December 22, 1943) 

895-11 (RP-260) (P. S. Carter) . Derives formu- 
las and gives computed radiation patterns for dipole 
and loop antennas on cylindrical fuselages. Theo- 
retical patterns are computed for the antenna axis 
parallel, radial, and circumferential to the axis of 
the cylinder. Some patterns have been checked ex- 
perimentally and indicate radiation paths of an- 
tennas mounted on a fuselage in positions where the 
wings have negligible effects. 

(December 24, 1943) 

895-15 (RP-260) (R. S. Wehner) . Describes two 
methods for determining the constants of transmis- 
sion line matching sections and applies them to the 
synthesis of broad-band antenna matching sections. 
One is a graphical method for use with antennas 
which are flat enough to be matched by a simple 
series line section. The other is an approximate 
analytical method that is applicable to highly re- 
active antennas. 

(March 6, 1944) 

895-16 (RP-260) (P. S. Carter). Presents two 
charts which give values for the power limits of 
trailing wire antennas. The curves are based upon 
an altitude of 40,000 ft in wet air. One chart gives 
the safe minimum wire size for quarter-wave an- 
tennas for power ranging from 10 to 1,000 w. The 
other chart gives similar data for antennas varying 
in length from one-twelfth to dne-half wavelength. 

(March 10, 1944) 

895-17 (RP-260) (P. S. Carter). Discusses the 


444 


APPENDIX 


effects of .antenna coupling upon pattern distortion 
change in input impedance and reaction between 
transmitters. Data are given to permit selection of 
locations for two antennas to have a degree of 
coupling below any specified value. The theory pro- 
vides partial prediction of the interaction for a sys- 
tem of four antennas. Tests are suggested for 
determining the maximum degree of coupling allow- 
able before serious trouble develops from the re- 
action between transmitters operating at nearly the 
same frequency. 

(April 11, 1944) 

895-21 (RP-260) (N. E. Lindenblad). Gives pre- 
liminary results of measurements on a 1,200-ft wave 
antenna over Rocky Point soil and compares them 
with results obtained with vertical radiators. For 
the major portion of the 200- to 8,000-kc range the 
wave antenna shows greater than a 12-db gain in 
the transmitting direction. The gain may be in- 
creased by paralleling of wires. Except for ground 
conditions corresponding to salt marsh, the use of 
wave antennas for transmitting seems to be per- 
tinent and attractive. 

(May 2, 1944) 

895-23 (RP-260) (W. A. Miller) . Gives pre- 
liminary results of measurements on 1,200-ft wave 
antennas over Tobyhanna, Pennsylvania, soil, which 
is wet, heavy loam. The wave antenna is found to 
have a gain of 10-12 db over a 30-ft vertical an- 
tenna at 200-2,000 kc. 

(June 20, 1944) 

895-24 (RP-260) (R. S. Wehner). Gives the im- 
pedance characteristics for a broad-band inverted-L 
antenna which has been modified so as to have two- 
thirds the height of a conventional quarter-wave 
stub and so as to be conveniently matched to a 
50-ohm line over frequency bands approaching 60 
per cent in width. The modification is a sleeve ex- 
tension of the outer conductor of the feed line, which 
has a much greater diameter than the horizontal 
conductor of the antenna. The characteristics and 
the radiation pattern indicate that the antenna is 
practical for use on aircraft at frequencies less than 
150 me. 

(July 20, 1944) 

895-27 (RP-260) (R. F. Franklin). Gives pre- 
liminary results of measurements on wave antennas 
over sandy soil. The antennas tested were one-, 
two-, and four- wire, 1,200 ft and 2,250 ft long, and 
one- and two-wire, 3,600 ft long, over a 200- to 
2,000-kc range. The tests indicate better perform- 
ance over sandy soil than over wet, heavy loam. 
Except for high frequencies the wave antenna per- 


formance is inferior to that of a vertical quarter- 
wave balloon-supported antenna. 

(August 28, 1944) 

895-29 (RP-352) (R. S. Wehner). Describes a 
simple coax-fed V dipole u-h-f antenna for hori- 
zontal polarization. Impedance and pattern data 
are presented to indicate that the antenna may be 
useful over frequency bands approximately 35 per 
cent wide. An assembly drawing is given for one of 
a series of four to cover a combined 500- to 1,500-mc 
range. 

(October 19, 1944) 

895-31 (RP-260) (P. S. Carter). Discusses the 
radiation characteristics of circular loop antennas 
at high frequencies. Formulas are derived and 
curves are given to show radiation resistance versus 
loop size and also the voltage induced in a receiver 
loop. A few patterns are also given to show the dis- 
tribution of radiation from loops of one wavelength 
and one-half wavelength circumference. The curves 
cover loops of any size having the natural approxi- 
mately sine-wave current distribution. 

(January 10, 1945) 

895-32 (RP-260) (N. E. Lindenblad) . Describes 
and gives test measurements of wide-band slot an- 
tennas having a 30 per cent bandwidth when ac- 
cepting a 2:1 standing-wave ratio tolerance. Such 
performance is obtained without the aid of com- 
pensating transmission line elements. 

(March 26, 1945) 

895-33 (RP-260) (R. S. Wehner) . Describes the 
graphical computation of two-element broad-band 
matching sections (2:1 standing-wave ratio for 
bandwidth greater than 30 per cent) by means of 
two charts. The charts solve the problem of match- 
ing a series resonant antenna (resonant resistance 
greater than 2-5 ohms) to a 50-ohm transmission 
line by means of an L-type circuit consisting of an 
antiresonant shunt section followed by a series 
transformer. 

(February 2, 1945) 

895-35 (RP-260) (R. S. Wehner). Describes an 
u-h-f zero-drag aircraft antenna consisting of a 
sleeve antenna mounted axially in a semicylindrical 
cavity recessed into the skin of a plane. The physi- 
cal dimensions are small enough to be practical at 
frequencies higher than 300 me. The impedance and 
pattern characteristics suggest its use for altimeters, 
guided missiles, tail warning, and IFF, using either 
vertical or horizontal polarization. 

(January 15, 1945) 

940-5 (C. R. Burrows). Presents and describes 
charts for determining the factors to be used in the 
design of admittance transforming networks, such 


RCM EQUIPMENT 


445 


as : ^re used in matching the plate circuit of a 
vacuurEi tube to an antenna. A pi network is 
used itpl transform one complex admittance into 
another.; 

96i5-5 (W. C. Babcock). Gives formulas and 
curves for approximate values of the average char- 
acteristic impedance of fan dipoles. The computed 
values are found to average about 10 per cent higher 
than values determined by impedance measure- 
ments. 

(May 24, 1943) 

966-8 (W. C. Babcock). Gives approximate for- 
mulas and curves for the average characteristic 
impedance and multiwire cylindrical cage dipoles. 

(July 1, 1943) 

966-14 (S. A. Schelkunoff) . Compares the meas- 
ured and theoretical impedance characteristics of 
cylindrical radiators by means of a series of curves 
which show fair agreement between theory and 
experiment. 

(June 28, 1943) 

966-15 (W. C. Babcock). Consists of charts and 
comments on computed values for the input im- 
pedance of hollow cylindrical dipoles with charac- 
teristic . impedances varying from 250 to 600 ohms. 
For characteristic impedances less than 300 ohms it 
is. noted that the input impedance tends to flatten 
out over a rather broad band between the first and 
second antiresonant frequencies and that it is closely 
resembled by the input impedance of a 60-degree 
conical dipole. 

(August 25, 1943) 

966-38 (RP-410) (W. C. Babcock, E. 0. Ber- 
nard, C. R. Eckberg, M. C. Francis) . Describes the 
stingaree trailing coaxial dipole airborne antenna 
designed for use against German tank communica- 
tions in the 27- to 33-mc band and 40-mc region. 
The antenna consists of two hollow radiators each 
about 1 in. in diameter and one-quarter wavelength 
in length, with a coaxial feeder passing through one 
of thein in order to reach the center of the dipole. 
The 50- to 100-ft coaxial feeder serves as a towing 
line and prevents any serious distortion of the radia- 
tion pattern by the plane. This antenna has a 20 
per cent bandwidth over a 2 : 1 standing- wave ratio 
and may be used with many different types of 
planes. Vertical polarization is provided by a 30-lb 
weight at the end of the antenna and horizontal 
polarization, by a small wdnd sock. The report gives 
results of preliminary tests. 

(December 9, 1944) 

966-47 (RP-410) (M. E. Campbell, C. R. Eck- 


berg, M. C. Francis). Gives stingaree antenna pat- 
terns at 30 me, supplementing those in 966-38. Field 
tests indicate that the antenna can be satisfactorily 
towed and that pattern shape is not materially 
affected by the length of the cable outside the air- 
craft. (Length of 20-40 ft recommended for 30 me.) 
The vertically poled pattern is reasonably circular 
when aircraft is less than 10 degrees above the 
horizon. At higher angles the energy is greater in 
front of the aircraft. 

(March 15, 1945) 

1045-6 (RP-992) (R. F. Lewis, G. H. Klemm) . 
Constructional data on a sleeve antenna for re- 
ceiver-transmitter use in the 350- to 400-mc range. 
The antenna is designed for vertical polarization 
when mounted on the under surface of an aircraft. 
An included curve sheet shows standing-wave ratio 
to 63-ohm line to be 2:1 for 350-410 me, 3:1 for 
210-430 me, and 10:1 for 180-520 me. 

(April 17, 1944) 

1045-7 (R. F. Lewis, G. H. Klemm). Construc- 
tional data on sleeve antenna for use with a 150- to 
450-mc receiver. The antenna is designed for ver- 
tical polarization when mounted on the under side 
of an aircraft. An included curve sheet shows stand- 
ing-wave ratio to 63-ohm line to be 2:1 for 305-360 
me, 3:1 for 190-380 me, and 10:1 for 150-450 me. 

(April 17, 1944) 

1305-1 (RP-382) (L. K. Findley). Gives pre- 
liminary measurements for patterns of antenna on 
model of German Hs-293 glider bomb. 

(April 24, 1944) 

1305-10 (RP-402a) (N. E. Klein) . Describes the 
CLU-24314 antenna switching unit for selectively 
connecting a coaxial input cable to any one of eight 
coaxial antenna feeders. 

(April 17, 1945) 

1305-19 (RP-402b) (N. E. Klein). Describes a 
remote-control antenna transfer switch for connect- 
ing a single coaxial line with any one of six other 
coaxial lines. A similar manually controlled model 
is also mentioned. 

(August 31, 1945) 

1305-TM2 (0. H. Schmidt). Describes an r-f 
dummy load having a fixed resistive impedance over 
a 500-mc range and capable of dissipating 1,500 w. 
The load surrounds the end of an r-f cable and con- 
sists principally of a brass block containing a slot 
through which salt water is circulated at a constant 
rate. Rise in temperature determines the amount of 
power dissipated. 

(August 31, 1945) 


446 


APPENDIX 


5 COAXIAL CABLE, WAVE GUIDES, 
AND FITTINGS 


411-TM-30 (W. W. Salisbury). Analyzes the 
effect of copper losses (due to skin effect) on the 
group velocity of radio waves in a coaxial line and 
concludes that the formula should be 


L.C.(l+|) 


where 

411-TM-130 (G-400, RP-107) (P. J. Sutro) . Pre- 
sents and compares the accuracy of three formulas 
for computing the characteristic impedance of a 
shielded balanced line composed of two inner con- 
ductors symmetrically placed within a cylindrical 
shield. The most convenient formula is found to be 


Zo 


120 


-1 



1 +y (1 -x*)J’ 


where e = dielectric constant of the dielectric filling 
the line, x = r/s, and y = s/R, with s = distance 
from center of shield to center of one conductor, 
r = radius of one conductor, and R — radius of 
shield. This formula is sufficiently accurate for most 
purposes if x and y are not too large. It should be 
noted that x and y are always less than unity. 

411-TM-85 (G-409, RP-107) (P. J. Sutro) . De- 
rives equations for the frequency bandwidths of 
resonant-line sections with and without resistive 
loads. The terminating reactance with which a sec- 
tion is resonated is either in parallel or in series with 
the section and the generator. Equations are also 
derived for the change in frequency band produced 
by a change in the mode of resonance, whether the 
mode be shifted by changing the physical length of 
the section or by changing the frequency. In an 
appendix the equations are used to determine the 
characteristic impedance (Zc) which provides op- 
timum bandwidth from an oscillator consisting of 
a section of coaxial line resonated with the inter- 
electrode capacitance of an oscillator tube connected 
in parallel with a load resistance. For first-mode 
operation the relation between the bandwidth and 
Zc is given by the equation. 

Q = . 

where Q = resonant frequency/frequency band- 
width, 

R = total resistance seen at resonance, 

0) = 2jt:/, 

C = interelectrode capacitance of oscillator 
tube. 


In practical cases an increase in Zc is thus seen to 
increase the first-mode bandwidth. A shift to a 
higher mode, however, is mathematically found to 
cause a decrease in bandwidth. Consequently, if the 
oscillator is to be operated in more than one mode, 
it is generally advantageous, in contrast with usual 
practice, to make Zc as small as possible. This pro- 
vides a more uniform bandwidth over all modes and 
extends the frequency range of the first mode while 
increasing the bandwidth in the higher modes. 

411-TM-132 (G-409, RP-107) (P. J. Sutro). 
Considers the theory of mode separation in a stand- 
ard coaxial oscillator using two sections of coaxial 
transmission line as resonant circuits. From calcu- 
lated graphs it is shown that the mode separation 
(the difference in the setting of one of the sections 
for the two modes) increases with the difference 
between the products of terminating capacity and 
the characteristic impedance for the two sections. 
The mode separation is seen to vary quite slowly as 
a function of frequency. 

411-TM-118 (M-lOO, RP-306) (C. M. Daniell). 
Details procedure in measuring the relative power 
supplied to a load through a coaxial transmission 
line. The method consists of inserting a probe volt- 
meter into notches cut in the line at small intervals 
compared to the wavelength in order to determine 
the maximum and minimum crest voltages along the 
line. Then the power in watts is proportional to 

Rmax Emin. 

411-255 (A-4300, RP-405) (J. C. Turnbull, J. R. 
Duggan, R. W. Green). Reviews measurements on 
wide-band coaxial lines preliminary to development 
of line to transmit 1 kw wdth minimum standing- 
wave ratio and attenuation for frequencies in the 
range from 500 to 2,500 me. Tests showed that 
beaded lines are unsatisfactory because of reflec- 
tions. The best line for low reflection and attenua- 
tion appears to be a longitudinally supported line 
using %-in. polystyrene tubes to support the inner 
conductor. 

411-123 (R-1000, RP-107) (W. G. Wadey, T. E. 
Moore). A plotted curve showing the results of 
measurements of the attenuation of RG-21/AU 
cable. Over the range from X = 3 cm to X = 15 cm, 
the data lie close to the curve a = 3.8 X — f. No 
change in the loss was observed when the cable was 
handled. 

411-TM-17 (Z-801) (L. T. Slocum). Contains 
curves showing the power loss in various lengths 
of Federal B-45 cable at frequencies from 100 to 
3,000 me for a 1:1 standing-wave ratio. 

411-237 (U-1600, RP-472) (J. G. C. Swinney). 
Summarizes RRL accomplishments in the design 


RCM EQUIPMENT 


447 


and testing of wide-band r-f coaxial (and wave- 
guide) connectors and fittings. Included are sug- 
gestions for future standardization. 

411-293 (J. R. Marshall). Describes equipment 
and methods used in voltage standing-wave ratio 
measurements on connectors, adapters, antennas, 
etc., in 90- to 10,000-mc range. Details are given 
on M-115 slotted lines for the 90- to 2,000-mc range, 
U-1202 measuring lines for the 2,000- to 3,500-mc 
range, and U-1600 lines for the 3, 500-10, 000-mc 
range. 

411-TM-118 (M-lOO, RP-306) (C. M. Daniell). 
Details procedure in measuring the relative power 
supplied to a load through a coaxial transinission 
line. The method consists of inserting a probe volt- 
meter into notches cut in the line at small intervals 
compared to the wavelength in order to determine 
the maximum and minimum crest voltages along 
the line. Then the power in watts is proportional to 

Emax -^min* 

411-255 (A-4300, RP-405) (J. C. Turnbull, J. R. 
Duggan, R. W. Green) . Reviews measurements on 
wide-band coaxial lines preliminary to development 
of line to transmit 1 kw with minimum standing- 
wave ratio and attenuation for frequencies in the 
range from 500 to 2,500 me. Tests showed that 
beaded lines are unsatisfactory because of reflec- 
tions. The best line for low reflection and attenua- 
tion appears to be a longitudinally supported line 
using %-in. polystyrene tubes to support the inner 
conductor. 

411-137 (R-1000, RP-107) (T. E. Moore, W. G. 
Wadey). Discusses the use of a variable-length 
resonant probe in wave guide as the reflecting ele- 
ment in a simple tunable stop-band filter for de- 
termining the frequency of signals received by 
AN/APR-5A. The method was found to be unsatis- 
factory. Determination of the frequency of weak 
signals will probably be difficult because of an 8- to 
10-db off-resonance attenuation. At wavelengths 
below 4.5 cm the attenuation drops off and at wave- 
lengths greater than 7.5 cm there is too small a 
rate of change in probe length with resonant wave- 
length. 

411-138 (R-1000, RP-107) (T. E. Moore, W. G. 
Wadey). Presents preliminary results of measuring 
the sensitivity of AN / APR-5 A in wave guide, for 
each of the possible harmonics over the 3- to 10-cm 
range. The purpose was to determine the expediency 
of operating the receiver at frequencies above 6,000 
me. The sensitivity (r-f power necessary to produce 
an audio signal power equal to the noise power) was 
found to range from lO”"^^ w at 10 cm to 10~'^ w at 
3 cm, being about the same for each of the oscillator 


harmonics out to the 9th. More complete and cor- 
rect data are to be given in 411-152. 

411-147 (R-1000, RP-107) (T. E. Moore, W. G. 
Wadey). Describes experiments in measuring the 
electrical effect of, and in preventing the condensa- 
tion of, atmospheric moisture in wave guides used 
for r-f transmission between an antenna and a 
search receiver. The moisture condensed on 4 sq in. 
of wave-guide wall, cooled below the dew point, 
caused a 10 per cent reduction in power transmitted 
at 11 cm. Condensation can be effectively prevented 
by circulating the air in the wave guide through a 
desiccator using magnesium perchloride or silica gel. 

411-149 (R-1000, RP-107) (T. E. Moore, W. G. 
Wadey). Illustrated description of materials and 
methods to be used in a wave-guide installation for 
AN/APR-5A. 

411-79 (R-715, RP-286) (R. H. Hoglund, A. J. 
Yakutis, J. S. Foster). Describes three wide-band 
wave-guide mixers, one for the 5- to 10-cm range 
and the other two for the 3- to 6-cm range. The 
former is a straight, terminated guide with which 
impedance matching is obtained by nonuniform 
cross section; it was designed to replace the mixer 
used in A-2700 receiver, whose characteristics are 
less uniform. One of the 3- to 6-cm mixers is a 
reduced scale model of the 5- to 10-cm design, and 
the other obtains a voltage maximum at the crystal 
by means of a wave-guide loop. 

411-1150 (Q-1900, RP-442) (P. I. Richards). 
Finds that the optimum response of nonresonant 
u-h-f coupling circuits having a specified form is 
independent of the type of coupling, whether shunt 
or series reactance, loops, nonresonant irises, etc. 
The response is found to depend upon the number 
of resonant cavities, the bandwidth, the center fre- 
quency, and the allowed-mid-band loss. Any change 
in the allowed decibel loss in the pass band has a 
certain maximum effect that is independent of the 
number of cavities. The optimum responses for from 
one to six coupled circuits are shown by curves of 
insertion loss versus ratio of frequency difference to 
bandwidth. There are also graphs comparing experi- 
mental with theoretical results on two types of 
wave guide coupled circuits. 

411-186 (Q-1900, RP-442) (S. B. Cohn). Pre- 
sents a method for the design of broad-band wave 
guide-to-coax junctions to be used with wave-guide 
filters requiring coaxial terminations. The report 
includes a brief discussion of pertinent transmission 
line theory, description of various types of junc- 
tions, and an account of the test method used. One 
type of junction (tapered ridge) has a bandwidth 


448 


APPENDIX 


ratio of 2.7 to 1 with a voltage standing-wave ratio 
of less than 2 to 1. 

411-201 (Q-1900, RP-442) (S. B. Cohn, P. I. 
Richards). Considers the effect of improper termi- 
nation on insertion loss in the filter pass band. 
Formulas and curves are given for maximum and 
minimum possible mismatch and insertion loss 
values in receiver r-f lines in which filters are in- 
serted. An important conclusion is that standing- 
wave ratios should be kept lower than is ordinarily 
assumed. The data show that a filter acts properly 
only when it is terminated at both ends in the im- 
pedance for which it is designed. 

411-211 (Q-1900, RP-442) (S. B. Cohn). Ex- 
plains the properties of ridge wave guide, a rec- 
tangular guide with a rectangular ridge projecting 
inward from one or both sides. By means of devel- 
oped equations and curves this type of guide is 
proved to have a lower cutoff frequency and im- 
pedance and a greater higher-mode separation than 
a plain rectangular guide of the same width and 
height. Experiments show a high degree of accuracy 
for the equations. Ridge wave guide has been suc- 
cessfully used as matching or transition elements in 
guide-to-coax junctions (411-186), as filter and 
cavity elements, etc. (411-229, and 411-221). 

411-221 (A-9000, RP-461a) (H. C. Early) . De- 
scribes a broad-band directional pickup and watt- 
meter for wave guide or coaxial cable. The pickup 
consists of a small loop or probe each of whose ends 
is terminated in a piece of lossy cable. The design 
with respect to the electric and magnetic fields in 
the wave guide is such that the power in one piece 
of cable is proportional to that in the forward wave, 
whereas the power in the other piece is proportional 
to the reflected wave. The difference between the 
two, as read by means of a microammeter and 
thermocouple connected to the forward piece, is then 
proportional to the net power into a load or antenna 
connected to the wave guide or coaxial cable. Such 
a wattmeter provides satisfactory readings in the 
range from 8 to 12% cm. 

411-229 (A-9000, RP-461) (H. C. Early). De- 
scribes a tapered steelridge wave-guide dummy 
antenna for the 8- to 12-cm range. It can dissipate 
1,000-w continuous wave without artificial cooling. 
The rugged mechanical construction of this dummy 
load for wave guide makes it suitable for naval use. 

411-253 (C-3306, RP-481) (P. A. Pearson). 
Finds that the energy loss due to moisture conden- 
sation in wave guide is seldom appreciable unless 
very large drops and puddles are formed. Measure- 
ments of attenuation in 1%- by 3-in. wave guide at 
3,000 me increased from 0.003 db per ft for a light 


film to 0.005 db per ft for large drops to 1.7 db per 
ft for large drops and puddles. Sea water caused 
slightly less loss than distilled water. Measurements 
also indicated that power loss is approximately 
linear with standing-wave ratio, becoming 20 per 
cent for standing-wave ratio of 4. 

^ ^ NOISE SOURCES AND STUDIES 

411-1 (F-700) (5 . 'Dyer) . Illustrated descrip- 
tion of type 931 photoelectric electron multiplier 
tube, which provides theoretical gain as high as 
500,000 from low magnitude signal current resulting 
from minimum light input. Experimental circuit 
provides 95-pa output with practically uniform re- 
sponse throughout 5-mc bandwidth, and develops 
0.38 rms v of noise at grid of first amplifier. Report 
includes suggested methods for securing necessary 
1,200-v operating potential difference from typical 
power supply. 

411-26 (G-lOO, RP-181) (R. D. Sard). Calcula- 
tions of frequency spectrum of noise from 931 tube, 
including discussion of factors affecting it. Theoreti- 
cal results for 70 v per stage show constant output 
up to 100 me, after which output drops as frequency 
increases, being —1 db at 200 me and —6 db at 
500 me. With 70 v on each of first eight stages and 
400 V on last two stages the output drops to only 
—4 db at 600 me. These results lead to the conclu- 
sion that a net accelerating voltage of 1,500 v gradu- 
ated from stage to stage would probably permit use 
of tube as direct-noise source in the 550- to 600-mc 
range. 

411-57 (H-201, RP-187) (J. D. Cobine, C. J. 
Gallagher). Report of experiments on operating 
characteristics of 931 tube between 50 and 5,000 kc 
indicates that gain may safely be assumed to be at 
least 75,000 with 100 v per stage and 0.001 1. In 
going from 50 to 5,000 kc the noise output drops 
about —3 db. Because first 15 min of operation 
causes a decrease of 4 db in noise output, the illumi- 
nation of the photo-cathode should then be in- 
creased to produce relatively constant output. One 
out of every five or six tubes has to be rejected be- 
cause of erratic performance. Higher operating volt- 
ages can be used to increase the noise output if a 
pressure chamber be provided to prevent breakdown 
at high altitudes. The report includes circuit dia- 
grams and graphs of results. It states that the noise 
is principally due to amplified shot effect in the 
first stage. 

411-TM-119 (H-200, RP-187) (C. J. Gallagher) . 
Life tests on 931 A phototube show average life of 
110 hr. 


RCM EQUIPMENT 


449 


411-68 (H-200, RP-187) (J. D. Cobine, C. J. 
Gallagher). Investigations of the 50- to 5,000-kc 
spectra of 11 types of gas tubes indicate RCA-884 
as the most promising noise source, followed by 
RCA-24G, WL 629, and WE 256A. By placing the 
tube in a strong magnetic field (1,000-1,500 gauss) 
to suppress objectionable variable-frequency oscil- 
lations it produces a relatively high-level spectrum 
free from peaks and holes. Under normal operating 
conditions with 30-ma plate current and 550-ohm 
output resistor, the 884 gives output voltages of 
2.8 at 50 kc, 7.5 at 2 me, and 1.1 at 5 me, as com- 
pared to 0.55, 0.46, and 0.38 v, respectively, as 
obtained from the type 931 tube with 1-ma plate 
current and 75,000 gain. The output remains prac- 
tically constant for long periods of operation. The 
report contains tables and performance graphs for 
each type of tube tested. It suggests that maximum 
output can be obtained by orienting the tube with 
respect to the magnetic field. 

411-TM-l (H-200, RP-187) (J. D. Cobine). 
Early investigation of use of type 884 tube as a 
noise source. Conclusions are practically the same 
as later reported in 411-68. 

411-TM-31 (K-400, RP-186) (D. A. Peterson) . 
Summarizes observations of the performance of the 
type 884 gas tube (not operated in magnetic field) 
as a noise source for an a-m radar jammer. The out- 
put was found to include oscillations which so 
masked the noise output as to make the tube much 
less effective than a type 931. Furthermore the 
energy distribution is so lacking in uniformity as 
to make difficult its adaption for use in a broad- 
band modulated jammer. 

411-TM-116 (H-200, RP-187) (J. D. Cobine, 
C. J. Gallagher, P. S. Jastram). Reports on the 
l-f noise spectrum of the 884 gas triode used with- 
out a magnetic field for frequencies below about 
100 kc. The average spectrum for 15 tubes which 
were tested shows a practically constant noise out- 
put of 66 db from 70 c to 100 kc. The output in- 
cludes a natural oscillation, usually about 100 kc, 
which must be filtered out to prevent overloading 
of amplifier tubes. 

411-TM-3 (RRL-H-200, RP-187) (J. D. Cobine). 
Gives results of tests of the noise output of the 
FG178A thyratron in the frequency range from 0.1 
to 9 me under various conditions. Spectral curves 
corresponding to optimum conditions show that 
when the tube is placed in a 1,000-gauss magnetic 
field the output varies from 80 db above lOpv/kc^^ 
at 0.1 me to 45 db at 5 me to 30 db at 9 me, as com- 
pared to a practically 4-db (or 3-db) output from a 
type 931 throughout the same range. (All figures are 


approximate.) The rms integrated voltage over this 
range is about 1.6 with a peak of about 6 v. For 
h-f applications, components below 100 kc should 
be suppressed because of the possible presence of 
relatively l-f oscillations. The tube must be oriented 
relative to the magnetic field in order to provide 
maximum noise output. 

411-TM-38 and 38A (H-200, RP-187) (J. D. 
Cobine). Gives results of tests of the noise output 
of Sylvania 2C4 cind 6D4 miniature gas triodes in 
the frequency range from 0.1 to 5 me under various 
operating conditions. The two tubes have the same 
noise spectrum and level and are the most efficient 
of those yet reported in this series of investigations. 
With a 300-gauss magnetic field and an anode cur- 
rent of 5 ma, the noise output varies from 65 db 
above lOpv/kc^'^ at 0.1 me to 76 db at 1 me, drops 
to 46 db at 5 me and to 27 db at 9 me. The rms 
integrated voltage over the 0.1- to 5-mc range is 
2.1 with a peak of about 6 v. 

411-92 (H-200, RP-187) (J. D. Cobine). De- 
scribes methods and gives results of testing the 
noise output of 6D4 in the range from 25 c to 100 kc. 
With normal heater current, 5-ma anode current, 
and 300-gauss transverse magnetic field, the tube 
produces noise at a level of 10 mv/kc^^ with little 
variation from tube to tube. This can be increased 
to 1 v/kc^ by connecting a 0.0005-mfd capacitor 
from anode to cathode and using a 600-gauss field. 
These conditions are satisfactory for either spot 
radar or communications jamming. Random pulses 
suitable for communications jamming may be pro- 
duced by the use of a 0.004-mfd capacitor between 
anode and cathode with proper adjustment of mag- 
netic field and anode current; the resulting noise has 
a level of about 8 v/kc^/^ between 1 and 6 kc. 

411-TM-115 (H-200, RP-187) (J. D. Cobine). 
Reports on the l-f noise spectrum of the 6D4. In a 
300-gauss magnetic field the noise output is prac- 
tically constant at 60 db above lOpv/kc^^ from 25 c 
to 100 kc. The rms voltage integrated over this 
range is 0.1 v with a peak of 6 v due to maximum 
output at about 1 me. Placing a 0.0005-mfd ca- 
pacitor between anode and cathode increases the 
output by about 20 db and introduces a peak of 
18 V due to an oscillation at 200 kc. When this peak 
is filtered out to prevent overloading of amplifier 
tubes, the noise should be suitable for both spot and 
communication jamming. The use of an 0.004-mfd 
capacitance and simultaneous adjustment of anode 
current and magnetic field strength raises the noise 
output to about 110 db in the range from 1 to 10 kc, 
with a peak noise at about 140 v. This should be an 
excellent noise source for communication jamming. 


450 


APPENDIX 


411-TM-36 (H-200, RP-187) (J. D. Cobine). 
Gives results of tests of the noise output of the 2D21 
miniature gas tetrode in the 0.1- to 9-mc frequency 
range under various operating conditions. Spectral 
curves show that for normal connection in a 1,200- 
gauss magnetic field the output is practically con- 
stant at about 70 db for the frequency range from 
0.12 to 1 me, dropping to 46 db at 5 me and to 30 db 
at 9 me. The noise has a peak of about 5 v. For most 
effective jamming, the circuit should attenuate fre- 
quencies below about 200 kc. 

411-TM-121 (H-200, RP-187) (C. J. Gallagher). 
Investigations of the noise output of GL-546 indi- 
cate too much variation to justify use as noise 
source. 

411-90 (G-105, RP-181) (D. Middleton). Cal- 
culation of the effect of rectification and clipping on 
the output spectra of 604, 884, 178 A, and 2021 
noise sources shows that clipping spreads the spec- 
trum and lowers the output level in all cases. The 
6D4 yields the greatest spectral spread, closely 
followed by the 884 and 2D21. A biased quadratic 
rectifier gives greater output spectral width than 
does a biased linear detector, if the ratio of cutoff 
voltage (relative to the operating point) to rms 
input noise voltage is less than about 2. The report 
includes a mathematical development of the theory 
and curves showing spectra for the four types of 
sources considered. 

411-97 (G-106, RP-181) (D. Middleton). Ex- 
tends the analysis of the effect of rectifying and 
clipping the output spectra of the 604 (as given in 
411-90) to include the effects of overloading the 
rectifier tube. Overloading is found to clip the “top” 
of the wave, whereas the cutoff of the tube clips 
the “bottom” and causes a wider spread in the 
spectrum. With an overloaded rectifier, whether 
linear or quadratic, the spread is greatest when the 
ratio of cutoff voltage (relative to the operating 
point) to rms input noise voltage lies between ±1.0 
and ±2.0. The linear is usually to be preferred be- 
cause of its generally higher output spectral levels. 
Optimum spread is provided by operation without 
overloading and by clipping the bottom of the input 
wave as heavily as possible within the limits of 
available gain. Severe clipping yields a consider- 
able spectral spread, but at prohibitively low levels. 
These conclusions are based upon a general mathe- 
matical analysis and upon a large number of com- 
puted performance curves of the 6D4 tube under 
various conditions of cutoff, saturation, and rectifier 
response. 

411-74 (H-200 & H-800, RP-187) (J. D. Cobine) . 
Design of 375-gauss permanent magnets and elec- 


tromagnets for 604 noise source. The permanent 
magnet consists of two Alnico bar magnets cast in 
an aluminum frame to give a weight of 9 oz, includ- 
ing the tube, as compared to 6 oz for the electro- 
magnets. The report includes photos, design details, 
field shapes, and test data. 

411-136 (H-200, RP-187) (D. Cobine, C. J. 
Gallagher, P. S. Jastram). This final report on the 
noise characteristics of Type 884 and 2050 gas tubes 
concludes that neither is as good as the 6D4 used 
with magnetic field. The conclusion is based upon 
measurements of output voltage uniformity, magni- 
tude of noise output, freedom from undesirable 
oscillation, and low power requirements. The noise 
spectrum of the 884 without magnetic field is fairly 
uniform from 25 c to 100 kc with a strong oscilla- 
tion at 100 kc which must be filtered out. Consider- 
able data are given on the tube-to-tube variations 
found with the 884. The output of the 2050, using 
the control grid as the anode, is relatively fiat from 
25 c to 30 kc with a strong oscillation at about 50 kc. 

411-TM-69 (H-200, RP-187) (P. S. Jastram). 
One-sided clipping of 604 noise output has two 
effects. First, the general level is reduced. Second, 
the low-frequency components (1-3 me) are reduced 
more than the high-frequency components (3-9 me) , 
making a flatter spectrum. For undipped noise the 
level at 5 me is 30 db below the 1-mc level, wRereas 
with extreme clipping the 5-mc level is only 11 db 
below the level at 1 me. 

411-76 (H-800, RP-187) (J. D. Cobine). De- 
scribes two 1-f noise generators using the 6O4 noise 
source. One (H-804) develops 180-v peak-to-peak 
noise voltage across a load of 4 kilohms. The other 
(H-805) develops 5-v peak-to-peak noise voltage 
across a load of 100 ohms. Both have a substan- 
tially flat noise spectrum from 500 c to 100 kc. In 
each the 6D4 is followed by a low-pass T filter to 
suppress frequencies higher than 100 kc. The decibel 
output is considerably increased by a capacitive 
shunt across the output of the 6D4 tube. With the 
high load impedance generator the noise is quite 
evenly clipped on both sides of the voltage wave. 
With the low-impedance generator the noise is quite 
strongly clipped on the negative side. The report 
includes photo, circuit diagram, and noise spectrum 
for each generator. 

411-169 (H-200, H-800, RP-187) (J. D. Cobine, 
J. R. Curry). Summarizes results of investigating 
behavior of 6O4 as noise source for the 0.5-mc to 
5-mc range. Based upon a large number of reported 
measurements, the recommended operating condi- 
tions are (1) the tube should be used with a 375- 
gauss permanent magnet oriented with field trans- 


RCM EQUIPMENT 


451 


verse to discharge path, (2) anode current 5 ma, 
(3) load resistance 20,000 ohms or higher. The 
spectrum maximum is then at 700 kc, the level is 
about 79 db above 10mv/\/kc, the peak-to-peak 
output is 18 V, and the rms voltage is 2.5 v. 

411-124 (H-205, RP-187) (P. S. Jastram). De- 
scribes a peak-reading voltmeter that may be used 
to measure random noise. The instrument has 1- to 
150-v amplitude range and a frequency coverage 
from 50 c to 30 me. The circuit, its operation and 
calibration, are described in detail, as are also the 
design principles. 

411-162 (H-200, RP-187) (J. D. Cobine, J. R. 
Curry). Describes a range extender for a sound 
analyzer (General Radio Type 760 A) whose upper 
limit is extended to 200 kc in order to facilitate 
noise measurements at higher frequencies. This is 
accomplished by means of an oscillator and tuned 
mixer to beat the noise at high frequencies down to 
a fixed frequency band on the 760A. The setting of 
the variable-frequency oscillator gives the frequency 
of the noise components being measured. 

411-225 (H-800, RP-187a) (J. R. Curry). Sum- 
marizes experience in equalizing noise amplifiers to 
provide a high noise level with approximately flat 
spectrum in the 0.1- to 5-mc range from a 6D4 (or 
931) source. Results are embodied in five schematic 
diagrams to be used by inexperienced builders of 
6D4 noise amplifiers for outputs of approximately 
60, 85, 95, and 100 db in the 0.1- to 5-mc range and 
120 db in the 0.5- to 2.5-mc range. (Zero 6 = lOpv/ 
\/RC.) Equalization is accomplished by manual 
adjustment of compensating circuits to give opti- 
mum indication on a spectrum analyzer to which a 
noise voltage is applied. A simple shunt or series 
peaking circuit is used for compensation at high 
frequencies and a parellel RC circuit in series with 
the load resistance for low frequencies. The report 
includes a brief, clear discussion of noise spectra, 
instantaneous, rms, and peak-to-peak voltages, 
clipping, and power, as well as their measurement 
and specification. Experimental results show the 
effect of clipping on the noise spectra, the unclipping 
effect of filters, and the amplifier response to noise 
and sine waves. 

411-232 (H-200, and G-107, RP-187 and 181) 
(J. D. Cobine, C. J. Gallagher, R. Weinstock, 
F. Bloch). Gives results of experimental and theo- 
retical investigations of the production of noise 
from hot-cathode gas tubes with and without an 
external magnetic field. Experiments on the effect 
of arc discharge in gases were made with spectrum 
analyzers and wide-band “scopes.’’ The discharges 


generate oscillations superimposed on random noise 
in a band having a width of several megacycles. 
There are both plasma-ion oscillations and oscilla- 
tions of ions in the cathode potential minimum. The 
oscillations may be suppressed by a transverse mag- 
netic field when the anode is so shielded that no 
electrons can reach it from the cathode. The mag- 
netic field also increases the level of the h-f compo- 
nents of the noise by focusing the ionizing electrons 
into a narrow region near a tube electrode. The noise 
level also depends upon the pressure, being highest 
at about 20 \i. The report includes a description of 
an experimentally developed tube giving a wider 
noise band than that from 6D4. 


411-239 (H-200, RP-187) (S. Ruthberg). Finds 
that cold-cathode gas-tube noise generators are less 
practical than the hot-cathode type because of the 
higher voltages and currents required. The dis- 
charges from the two kinds of tubes are similar in 
appearance and behavior. Types tested were the 
glow tube, mercury arc with mercury-pool elec- 
trodes, and a corona-discharge monocle. Of these, 
the glow tube is best for noise production con- 
trolled with a transverse magnetic field. The level 
and slope of its spectra compare favorably with 
those of 6D4, especially in the region up to 1 me. 

411-258 (H-200, RP-187) (P. S. Jastram, C. J. 
Gallagher). Discusses the theory and operation of 
the 6D4 spectrum checker, an instrument which in- 
dicates the spectral distribution of the noise from 
an available gas triode in the range from 100 kc to 
5 me. The device comprises a two-stage amplifier, 
filters, diode rectifier, and meter. The results of a 
sample set of measurements are tabulated. 

411-260 (H-200, RP-187) (P. S. Jastram). Ex- 
haustively summaries and discusses the elementary 
theory of noise. 

778-8 (NDRC-C63) (M. E. Campbell). Gives 
the circuit and characteristics for a voice-frequen^ 
noise generator employing a 2051 gas tube as the 


oise source. 

(January 30, 1943) 

931-5 (RP-243) (L. R. Roller). Discusses the 
onstriction oscillator as a noise source. This mer- 
ary-vapor discharge tube, wherein the arc passes 
irough a constriction between the anode and cath- 
de gives a nonuniform spectrum with an output 
ep’endent upon the pressure of the mercury vapor, 
^he tube life of 5-10 hr is limited by the sputtering 
f the cathode. The high rate of cleanup prevents 
he use of permanent gases instead of mercury. 

(November 20, 1943) 

966-4 (NDRC 15004) (H. H. Benmng). De- 


452 


APPENDIX 


scribes preliminary models of three types of a-f 
noise generators originally intended as modulation 
sources for communication transmitters which are 
converted to jammers. They are convenient for 
laboratory or training use. One consists of a motor- 
driven shaft in a cup of carbon granules. Another 
is a motor- vibrated carbon transmitter button. The 
third type uses a 2050 gas tube to drive a 6AG7 
amplifier. 

(May 26, 1943) 

1060-1 (462, RP-196) (A. M. Glover, R. W. 
Engstrom, W. J. Pietenpol) . Describes a grid-con- 
trolled photomultiplier (C-7102) and its application 
to regenerative amplification of noise output in the 
0-5 mc/sec range. With a tube similar to the 931-A, 
feedback from the ninth dynode to the grid is found 
to increase output noise by 10 db over 2-mc band- 
widths at any frequency up to 5 me. 

(May 16, 1944) 

1060-2 (462, RP-196) (A. M. Glover, R. W. 
Engstrom, W. J. Pietenpol). The final RCA report 
on the investigation and manufacture of noise 
sources. These include the 931-A, the C-7102, and 
the 884 with various gases. The 931-A is found to 
have better life than the 931 ; improvements possible 
from minor design changes are unimportant; com- 
plete redesign is impracticable. Facts relative to 
C-7102 are given in 1060-1. Helium gas in 884 is 
best adapted to noise production ; at optimum pres- 
sure of 700-750 |x only one-tenth as strong a mag- 
netic field is required to suppress oscillations as in 
the case of argon. 

(March 7, 1945) 

1176-1 (RP-311) (S. Ballantine). Gives the re- 
sults of tests of Tungar bulbs as noise generators. 
They show no special merit as compared with other 
gas tubes requiring less cathode power. 

(February 11, 1944) 

1176-2 (RP-311) (S. Ballantine, E. Osterland). 
Discusses the use of transformer coupling with gas- 
tube noise sources instead of the conventional re- 
sistance coupling. Circuits are given for type 884 
and 2050 tubes used for spot jamming of communi- 
cations from a 28-v d-c supply. No magnetic field 
is used. The behavior of the 2050 is found to be 
better than that of the 884. Output is not sufficient 
to provide 100 per cent modulation of transmitters. 

(January 6, 1944) 

1176-3 (RP-311) (E. Osterland). Reports the re- 
sults of noise source investigations at Ballantine 
laboratories. Studies were made of gas tubes, elec- 
trolytic interrupters, and spark gaps as noise 
sources for jamming communications. 

(August 1, 1944) 


MISCELLANEOUS RESEARCH 
AND DEVELOPMENT 

411-9 (A-700, RP-147) (R. B. Barnes). De- 
scribes three untuned receivers for detecting radar 
signals over wide ranges of carrier frequencies and 
repetition rates. Each consists of an antenna, r-f 
band-pass filter, crystal or diode detector, and audio 
amplifier. The filter is designed to make the receiver 
sensitive only to a selected r-f range. In the filter 
structure sections of coaxial transmission line are 
used in place of lumped inductances. Simple design 
formulas for the capacitances are given in terms of 
the upper and lower cutoff frequencies, section 
length, and desired characteristic impedance, with 
specifications and performance curves (theoretical 
and actual) for the 170- to 270-mc range. 

411-28 (A-700, RP-147) (S. B. Cohn). Contains 
design equations and performance curves for six 
u-h-f filters. The types include (1) low-pass for 
100-ohm load with cutoff at 150 me, (2) high-pass 
for 100-ohm load with cutoff at 150 me, (3) com- 
bined (1) and (2) in series, (4) band pass for 150- 
300 me for 42.5-ohm load, (5) band pass for 300-460 
me for 50-ohm load, and (6) band pass for 100-200 
me for 50-ohm load. Loaded short-section of coaxial 
transmission line are used as high-Q inductances 
for all cases. The capacitances are metal disks con- 
nected to the center conductor and closely spaced 
from the outer conductor by means of dielectric ma- 
terial. The report includes data on termination with 
either crystal or diode detector and practical infor- 
mation on construction. 

411-TM-102 (M-125, RP-306) (J. G. C. Swin- 
ney) . Briefly discusses the design, construction, and 
performance of a 75-mc low-pass filter using lumped 
constants. The filter is of standard design with 
M-derived end sections and a T center section 
working into a 50-ohm line. The discussion includes 
a graph of measured attenuation versus frequency 
and an estimate of 60 db attenuation at 75 me. 

411-113 (M-4601, M-4602, RP-286) (P. L. Har- 
bury). Design of one- and two-section high-pass 
filters with cutoff at 900 me when working between 
50-ohm terminations. Report includes application 
of design equations from 411-28 and sketches, at- 
tenuation characteristics, and standing-wave char- 
acteristics of the two filters. 

411-115 (Q-1600, RP-286) (P. I. Richards). 
Gives equations for designing resonant-section 
coaxial filters. The derivation of the equations is 
based upon a general method for analyzing all types 
of coaxial filters in terms of matrix notation, as ex- 
plained in some detail. Experimental measurements 


RCM EQUIPMENT 


453 


are given on four structures, including a tunable 
(13-7.5 cm) double-T band pass and a similar 
I section, an m-derived band pass, and a three-sec- 
tion band pass, all having relatively sharp cutoff. 

411-115A (Q-1900, RP-442) (P. I. Richards). 
Gives equations for designing an easily constructed 
high-pass coaxial filter consisting of several sections 
of coaxial line separated by capacitances. The equa- 
tions were derived by the method given in 411-115. 
Constructional details and performance curve are 
given for a 1,700-mc high-pass filter. 

411-115D (Q-1900, RP-442) (P. I. Richards). 
Supplements 411-115 by presenting improved de- 
sign equations and curves for seven types of reso- 
nant-section coaxial filters. 

411-163 (Q-1900, RP-442) (S. B. Cohn). Pre- 
sents design equations and curves for an easily con- 
structed microwave low-pass filter which may be 
built either in coaxial line or wave guide. Treatment 
includes elimination of spurious response and con- 
sideration of insertion loss. The method is exempli- 
fied by computing the dimensions for a 50-ohm 
termination coaxial filter having a pass band up to 
3,450 me, an attenuation of greater than 30 db 
above 4,050 me, and no spurious responses below 
10,000 me or near 24,000 me. Discontinuity capaci- 
tances at changes in cross section are taken into ac- 
count in the development of the design equations. 

411-115B (Q-1900, RP-442) (P. I. Richards). 
Derives design formulas for minimizing spurious 
responses in a low-pass filter that is designed in 
accordance with equations from 411-163. The for- 
mulas involve cancellation of some of the spurious 
pass bands in order to provide characteristics ap- 
proaching those of an ideal low-pass filter. 

411-161 (W. G. Wadey). Complete illustrated 
description and explanation of operating technique, 
including harmonic frequency chart for more ac- 
curate determination of frequency of high-pass 
filter with variable cutoff, 3,000-10,000 me (RP-107, 
R-1024) . This filter consists of a wave-guide section 
with a movable wall which can be adjusted from 
a fully open position for cutoff at 3030 me to a fully 
closed position for cutoff at an infinite frequency. 
The filter is built into 1 x 23/32-in. wave guide and 
is fitted with a calibrated dial reading directly in 
thousands of me. It may be readily adapted for re- 
mote reading and control through a flexible shaft. 
Designed for u-h-f operation of APR-5A, it is also 
useful in eliminating interference when searching 
for only higher-frequency signals. Another sug- 
gested use is as a “line stretcher” in wave guide. 

411-234 (Q-1900, RP-442) (S. B. Cohn, P. I. 
Richards). Is primarily concerned with the me- 


chanical design of u-h-f filters developed by the 
Q-1900 project. Emphasis is placed on the necessity 
for terminations in the characteristic impedance for 
which a filter is designed, and test procedures are 
given for insuring such terminations. A brief dis- 
cussion of discontinuity and other second-order 
effects is followed by suggestions for practical lay- 
out and construction of filter structures. 

411-240 (Q-1900, RP-442) (K. R. Spangenburg) . 
Gives the insertion loss versus frequency charac- 
teristics of band-pass filters composed of one, two, 
or three lossless resonant circuits in a loosely 
coupled cascade connection between a source and a 
load impedance. The effects of coupling upon band- 
width and insertion loss variations are also dis- 
cussed. The method of analysis depends upon find- 
ing the complex roots of the determinants of the 
mesh equations. The bandwidth of a three-circuit 
filter is found to be approximately 40 per cent 
greater than that of a two-circuit filter with the 
same coupling. 

411-281 (R. R. Rhigher, F. M. Gager) . Describes 
two methods for measuring insertion loss of micro- 
wave filters. The accuracy of one method depends 
upon the calibration of the attenuator of a signal 
generator. That of the other method depends upon 
the square-law operation of a crystal detector. 
Either method gives the attenuation in terms of the 
characteristic impedance insertion loss of the filter 
under test. 

411-21 (D-400, RP-178) (J. P. Woods). Con- 
tains complete data for design and construction of 
400- to 2,600-c transformers and chokes used in 
radio power supplies. Full information in the form 
of tables, graphs, and practical comments is given 
for designing power units ranging from 9 to 900 
volt-amperes as provided by nine sizes of RRL- 
standard-shape laminations with progressive factor 
of approximately 2. 

411-37 (D-400, RP-178) (J. P. Woods). Illus- 
trates and describes a three-element L-C network 
for regulating a-c voltage from a small variable- 
speed motor-generator driven by storage battery. 
The network maintains constant voltage output for 
reasonable variations in battery voltage, provided 
that the motor does not vary more than ± 10 per 
cent from its nominal speed, the generator has an 
approximately linear voltage-frequency character- 
istic, and the load has approximately unity power 
factor. 

411-78 (D-400, RP-178) (J. P. Woods). De- 
velops general principles, equations, and graphs to 
be applied in the design of small transformers work- 
ing in the frequency range from 100 to 3,000 me. 


454 


APPENDIX 


After proving that the power loss is minimized when 
the copper and iron losses are approximately equal, 
equations are developed to relate power loss and 
transformer weight to output volt-amperes, fre- 
quency, dissipation per unit surface area, iron and 
copper constants, and relative transformer dimen- 
sions. From these equations are determined the rela- 
tive dimensions for minimum transformer weight 
and per cent power loss. These establish an optimum 
shape for laminations, which is the basis for graphs 
showing the relations between output volt-amperes 
on the one hand and circular mils per ampere, flux 
density, and lamination width on the other. A final 
graph relates design frequency to output volt-am- 
peres per pound of transformer. These data are used 
in 411-21. 

411-264 (G-611) (D. Middleton). Develops an 
approximate theory for eddy-current loss in trans- 
former cores excited by video random noise and 
high-frequency (me) sine waves. Formulas and 
graphs showing the variation of skin depth and 
mean eddy-current loss with frequency and thick- 
ness of lamination are derived from a solution of 
the field equations governing the distribution of 
electric and magnetic fields in thin rectangular 
laminae. Skin depth is found to decrease with in- 
crease in frequency, thickness of lamination, and 
effective permeability and conductivity of the core. 
In voltage-fed transformers the mean loss is ap- 
proximately inversely proportional to the square 
root of the bandwidth. In current-fed transformers, 
it is directly proportional. Consideration of the ad- 
vantages and limitations of the theory and its ap- 
proximations and suggestions for reducing eddy- 
current losses are included in the report. 

411-244 (H-900, RP-187) (J. D. Cobine, J. R. 
Curry, C. J. Gallagher, S. Ruthberg). Outlines a 
procedure for designing video transformers for noise 
voltages. The procedure is based on exciting im- 
pedance and power loss (hysteresis and eddy) data 
for Hipersil, Monimax, and B9W4A. As a result of 
techniques for measuring these properties, which 
techniques are fully described, it is concluded that 
Monimax has the lowest losses wdth noise excitation. 
The data, both calculated and empirical, are shown 
by numerous curves. The procedure is applied to the 
design of two transformers operating in a Class B 
noise amplifier to deliver 350 w wdth a 2.5-mc band- 
width. 

411-67 (C. W. Oliphant) (Beaver I). Presents 
results of 10-day search watch at Bird Cape, 
Amchitka, near Kiska, in 180- to 225-mc frequency 
range. The search equipment comprised two S-27 
and one SX-28 receivers with CUO high-frequency 


converters and horizontal half-w'ave dipole anten- 
nas. All observed radar signals were believed to 
come from friendly sources. The report concludes 
with recommendations for future similar missions. 

411-TM-103 (A-3700, RP-321) (W. G. Dow). 
Gives tentative specifications for a 30-kw air-horne, 
9- to 12-kv, d-c power source to be installed in the 
bomb bay of a four-motored bomber. The equip- 
ment includes a 160-hp air-cooled auxiliary engine, 
flexible coupling and gear box, 40-kw, 400-c gen- 
erator, transformer, and rectifier tube rack. 

411-89 (R-2000, RP-306) (S. B. Cohn). De- 
scribes a system for measuring the frequency re- 
sponse and sensitivity of receivers operating in the 
range of frequencies from 50 to 1,000 me. The 
equipment consists essentially of a large, constant 
field strength, conducting ground plane (galvanized 
iron mesh) in which may be inserted a calibrated 
transmitting antenna (variable-length cylindrical 
stub adjusted to resonance) and a receiving antenna 
(type designed for ground plane mounting). The 
field strength of the receiving antenna is shown to 
be equal to 

'q 

^ volts/meter, 

where E is the voltage between the ground plane 
and the base of the transmitting antenna, d is the 
distance in meters between the antennas, R is the 
resonant resistance of the transmitting antenna 
{X = 0) , and G = gain of transmitting antenna 
compared to 1/2 dipole (G = 2 for V4 and 1.39 for 
3 X/4) . When all factors except E are held constant 
during a given frequency-response run, the field 
strength is directly proportional to E, as measured 
by an r-f voltmeter built into the base of the an- 
tenna. The usual procedure is to maintain E con- 
stant and read the receiver output. But if the re- 
ceiver does not obey a definite detection relation, its 
output can be held constant by varying E. Auxiliary 
equipment includes the r-f voltmeter (bolometer), 
70-db audio amplifier, a-f voltmeter, r-f signal 
generators with low-pass filters, and r-f voltage 
regulator. The details for this equipment and the 
operating technique are described in the report. 

411-TM-105 (R-2000, RP-306) (S. B. Cohn). 
Describes an r-f voltage regulator specifically de- 
signed for use with the equipment mentioned in 
411-89 and having many other possible uses listed 
in the document, which shows photos, block and 
circuit diagrams. The device automatically main- 
tains a constant r-f voltage level at any arbitrary 
circuit point. 

411-TM-99 (G-700, RP-299) (Donald Fo.ster) 



RCM EQUIPMENT 


455 


Concludes that the jamming of German altimeters 
in various tactical situations is impracticable not 
only because of the great power required but also 
because of doubt as to the value of doing it. 

411-TM-47 (D-419, RP-178) (J. P. Woods). 
Contains 16 plotted curves of 60-c sparkover tests 
across gaps in air at low pressures. Data cover 
sphere gaps, needle gaps, and glass bushings for 
various gap lengths and pressures. They indicate a 
general straight-line relationship between spark- 
over voltage and pressure. An additional curve 
shows the relationship between pressure in inches 
of mercury and altitudes up to 50,000 ft. 

411-TM-98 (R-1700, RP-117) (R. C. Raymond, 
S. B. Cohn). Describes a wide-band regenerative 
circuit which permits the reradiation and amplifica- 
tion of a signal on the frequency at which it is 
received. The radiating time is long compared to the 
silent period during which the signal is received. 
Lack of available personnel has prevented the final 
development and possible applications of the circuit. 

411-107 (Z-3600) (L. E. Rayburn, H. Kees). 
Preliminary experiments with broad-band signal- 
repeating systems, consisting of an APR-4 receiver, 
ARQ-8 transmitter, and an auxiliary mixer, indi- 
cate that each particular application requires a 
“tailor-made” installation. This requirement is due 
mainly to the large number of spurious responses in 
the receiver output to be retransmitted. The system 
will evidently work on almost any desired receiving 
and transmitting frequencies if the equipment be 
carefully installed with reference to location of re- 
ceiver, transmitter, and antennas. 

411-111 (Z-1500, RP-242) (R. L. Hammett). 
Comprehensive illustrated description of Raven in- 
stallations on Albatross I (Navy PB4Y-2 recon- 
naissance aircraft). Special emphasis is placed on 
the ten antennas variously used for search, jam- 
ming, and DF, showing patterns, standing-wave 
ratios, and test results as well as discussing their 
installation and use. Information is also given about 
the installation of AN/APA-17, AN/APA-24, 
AN/APR-1, AN/APT-1, AN/APQ-2, and wave 
guide for AN/APR-6. A number of installation fea- 
tures designed to reduce operator fatigue and to 
increase the utility of this type of aircraft when 
searching for enemy radars are also discussed. 

411-165 (S. W. Athey). Briefly describes ten 
available RRL films for instruction or demonstra- 
tion. Subjects covered by the confidential lists are 
the M-2600 direction finder, A-500 Tuba, Albatross 
I, Carpet spot jamming, E-510 high-pass filter, and 
Window against HPG radar. Those covered by the 
secret list are tests of Window against SCR-584, 


Window on SCR-648 radar, effects of jamming on 
SCR-521 radar, and E-2400 f-m complex target 
indicator. 

411-171 (R-900, RP-286) (P. I. Richards). De- 
rives probability formulas that two events, each 
recurring at a definite period and lasting for a 
definite time interval, will occur simultaneously at 
least once during some specified time interval. The 
results are applicable to such problems as finding 
the probability that within 5 min an aircraft can 
make radio contact with an air traffic control tower 
where a receiver is being tuned back and forth over 
a frequency band (the aircraft may be assumed to 
transmit a 5-sec call every 20 sec). From the 
formula it is also possible to find what should be 
done in order to improve the probability of contact. 
In general, the results are applicable to any prob- 
lem that reduces to a question of the overlap of 
rectangular waves. 

411-177 (J. G. C. Swinney). Gives design infor- 
mation on three types of probe voltmeters, their 
calibration and use in measurement of frequency, 
velocity of propagation or relative power in con- 
centric transmission line, adjustment of antenna 
systems and oscillators, and determination of the 
characteristic impedance of a transmission line. 

411-217 (G-2000, RP-349) (F. Bloch) . Discusses 
the theory and design of low -radar-reflectivity cable 
used in towing targets for antiaircraft practice. The 
sample cable consists of a core of stranded steel 
wires covered with a thin insulation of polyethylene 
over which is wound a protecting steel armor for 
the “open sections,” with a thin metal foil between 
the insulation and the armor for the “shorted sec- 
tions.” The “open sections,” because of forced cir- 
culation of electric current in the armor around the 
cable, have a higher inductance than the “shorted 
sections” with which they are alternated. The op- 
erating principle is that of a transmission line with 
periodically varying self-induction. The effective 
cross section of the fabricated cable is about one- 
fifth that of a continuous steel cable of the same 
dimensions, as confirmed by laboratory tests. 
Field tests have yet to prove whether this low re- 
flectivity is sufficient for practical protection. 

411-272 (G. E. Hulstede). Considers the effect of 
signal intercept probabilities on design of search re- 
ceivers and DF antennas. The probability informa- 
tion is obtained from a mechanical computer which 
simulates a radar signal and a receiving antenna, 
both sweeping in azimuth, and a search receiver 
sweeping in frequency, the sweep rates being adjust- 
able, as is also either the antenna beamwidth or 
receiver acceptance band. The recorded data are 


456 


APPENDIX 


plotted as curves to show various effects for given 
parameters. Curves indicate, for example, that less 
time is required to intercept a signal if the receiver 
has a high sweep rate, that intercept occurs more 
quickly as the acceptance bandwidth is increased, 
or that a rotating type of DF antenna causes a 
longer time between intercepts than does an omni- 
directional antenna. Such typical findings assist in 
solving design problems. 

411-276 (S. W. Athey and C. Gray). Considers 
methods for photo graphing cathode-ray tube 
screens, with special reference to the problems en- 
countered in RCM studies and investigations. 

411-285 (W-100) (R. K. Vermillion). Describes 
a high-speed linear sweep circuit suited for oscillo- 
graphic study of transient waveforms. The circuit 
includes means for producing a sawtooth pulse from 
either a positive or negative pulse, a means for ad- 
justing the time delay between the initial triggering 
pulse and the start of the sweep voltage, and a 
means ’for calibrating and adjusting the linearity 
of the sweep voltage. Circuit is designed for use with 
any conventional oscillograph having direct horizon- 
tal deflection plates and intensity grid terminals. 


RCM APPLICATIONS 

AIRBORNE RCM SYSTEMS 

966-51 (RP-440) (H. H. Penning, G. J. Heinzel- 
man). Describes communication Ferret C-1, a B-24 
plane equipped to search for and monitor enemy 
transmissions in the 0.55- to 200-mc range. Positions 
are provided for three operators each of whom han- 
dles an automatic search receiver and APA-23 
recorder, a manually operated monitoring receiver 
and voice recorder of transmissions observed 
thereon, and a second voice recorder of dictated 
data. Two modified R-45/ ARR-7 receivers are used 
for the 0.55- to 28-mc range, R-44/ARR-5 for the 
28- to 80-mc range, and R-54/ ARR-4 for the 80- to 
300-mc range. 

(June 8, 1945) 

966-52 (RP-440B) (E. 0. Bernard, C. R. Eck- 
berg). Describes modifications of R- 24 / ARR-5 for 
Ferret use in searching and monitoring the 28- to 
82-mc band. The changes permit satisfactory per- 
formance, as discussed in detail, when two receivers 
are operated from a single antenna or from the same 
power supply. 

(August 23, 1945) 


966-53 (RP-440) (R. V. Crawford). Describes 
modifications and performance of R-4o/ ARR-7 re- 
ceivers to permit operation of two on a single an- 
tenna and from a single power supply for Ferret use. 

(August 22, 1945) 

1045-TMl (BAD 100— BD 102, RP-986) (J. W. 
Keuffel). Describes modifications to Jacket AN/ 
ART-3 to correct defects that would prevent imme- 
diate operational use of experimental models. The 
report includes recommendations for future designs 
based on test experience. 

(September 7, 1944) 

1045-TM2 (RP-986) (D. K. Reynolds). De- 
scribes the procedure and gives the results of jam- 
ming trials of Jackal AN/ART-3. The general con- 
clusions are that German tank radio communication 
is effectively jammed when airborne Jackel sets are 
staggered in frequency and that SCR-508, -608, 
-509, and -609 are not severely affected. Ground 
trials indicated that this jammer when mounted on 
a truck or when installed on a hillside could be use- 
fully employed to cover confined areas. 

(August 21, 1944) 

1045-MR3 (D. K. Reynolds). Describes the in- 
stallation of Jackel AN/ART-3 in B-24 aircraft of 
the 8th Air Force. 

(August 17, 1944) 

1045-TM3 (RP-986) (R. C. King) . Describes the 
procedure and gives the results of field tests of 
Jostle IV in jamming German and American 30- to 
34-mc equipment. The results indicated more effec- 
tive jamming of German tank radio communica- 
tions (amplitude-modulated) than of SCR-609 
(frequency-modulated). Harmonic radiation from 
the jammer is negligible and the fundamental spec- 
trum is uniformly satisfactory. 

(February 23, 1945) 

966-13 (RP-236) (C. L. Cahill). Gives results of 
v-h-f jamming at Orlando. Jamming was successful 
whenever the jammer was closer to the receiver than 
was the signal transmitter. 

(September 22, 1943) 


72 OPERATIONAL CONSIDERATIONS 
AND TESTS 

966-17 (RP-326) (R. L. Robbins). Reports on 
slight RCM activities in Tennessee maneuvers dur- 
ing July 1943. Four ground-based jammers with 
20- to lOO-w output and improvised vocal or me- 
chanical noise were available. Most of the conclu- 
sions are of a tactical nature. 

(September 24, 1943) 


RCM APPLICATIONS 


457 


966-23 (RP-326) (R. L. Robbins). Reports radio 
activities in Tennessee maneuvers in autumn of 
1943. All operations were of too short duration for 
RCM to prove itself in a spectacular manner. 

(December 28, 1943) 

1045-2 (RP-987) (S. Hansen) . Describes the pro- 
cedure and gives the results of field tests of Peter 
in jamming a British 590-mc coastal radar from a 
British ship. Tests with an unmodified jammer and 
a jammer with a five-stage repeater amplifier (volt- 
age gain of 800) indicate that the amplification 
causes a small craft to appear as a cruiser to the 
radar operator. 

(January 10, 1943) 

1045-4 (RP-987) (S. Hansen, H. H. Race) . Gives 
results of field tests of Peter comprising an u-h-f 
amplifier having a voltage gain of 2,000 and a band- 
width of 14 me centered at 560 me. Using bare 
dipole antennas without reflectors and inclined 45 
degrees from horizontal (receiving 25 ft and re- 
transmitting 40 ft above water) the set gives an 
intensified echo equivalent to a destroyer at all 
ranges down to 5 miles. The tests indicate that the 
signal may be made to simulate a light cruiser either 
by adding reflectors or by increasing the mean 
antenna height to 45 ft. 

(February 4, 1944) 

1045-9 (J. T. Wilner, et al). Estimates the 
monthly RCM requirements of the 8th and 9th Air 
Forces as a minimum of 1,000 radar jammers, great 
quantities of communications jammers, and exten- 
sive facilities for investigating the characteristics of 
enemy radars. 

(June 20, 1944) 

1045-11 (RP-987). Recounts such American 

British Laboratory [ABL] activities for RCM 
phases of Neptune operation (the invasion of Nor- 
mandy) as may be of use in future operations. The 
chief work, aside from training operators and par- 
ticipating in basic planning and in field tests, was 
in correcting certain undesirable characteristics of 
the RCM equipments, particularly as regards inter- 
ference to other allied services. Much work was also 
done in installing and adjusting jammers on various 
vessels of the U. S. Navy. The report is terminated 
with brief mention of specific difficulties encountered 
with eXFR, TDY, British Carpet II, APR-1 with 
panoramic adapter, APR-6, and RDL-Blinker. 

(November 22, 1944) 

1045-MR2 (RP-984) (J. D. Noe). Describes the 
prototype installation and tests of AN/APA-17 in 
a B-17 aircraft. It is found that the accuracy of a 
bearing can be approximately judged by an experi- 


enced operator on the basis of the pattern displayed 
on the cathode-ray tube. Accuracy on a sweeping 
signal is less than on a locked signal and tends to 
be less on a lobe-switched than on a non-lobe- 
switched signal. Accuracy on a non-lobe-switched, 
locked signal appearing approximately fore or aft 
of the aircraft should be within ± 3 degrees. The 
report also describes the organization of 94th Bom- 
bardment Group for operational use of the equip- 
ment. 

(August 13, 1944) 

1045-MR5 (RP-984) (J. D. Noe) . Presents and 
analyzes data obtained by AN/APA-17 on 13 op- 
erational missions in the European Theater. The 
equipment is found to be suitable for determining 
locations of enemy radar, mapping radar-controlled 
flak areas, predicting flak in time for neutralizing 
or evasive action and for investigating the opera- 
tional procedure of enemy radars. High-caliber 
operators, well-trained, are essential. 

(October 27, 1944) 

1045-TM5 (L. B. Lusted). Gives data on AJ 
devices in a Small Wurzburg which had been cap- 
tured and assigned to ABL for repair and modifica- 
tion. The Window AJ devices included means for 
utilizing the doppler effect to distinguish between 
fast moving aircraft and slow moving Window, a 
differentiating circuit to distinguish visually be- 
tween a fixed target echo and the random character 
of the Window return, and a circuit for making the 
same distinction aurally. The AJ devices against 
jammers included means for quickly and easily 
shifting from a jammed to an unjammed frequency, 
DF means for measuring the bearing and elevation 
of a jammer, and means for measuring range by 
selecting the most favorable polarization in order 
to minimize the jamming. 

(March 21, 1945) 

1045-TM4 (J. G. Stephenson). Describes modi- 
fications to Rug and Carpet I and III for spot jam- 
ming. 

(February 27, 1945) 

1045-TM6 (RP-303) (G. H. Klemm) . Describes 
a modification Kit for AS-69/APT (M-2202) an- 
tenna for operation in the 450- to 500-mc band. 

(April 19, 1945) 

1045-TM7 (RP-987) (M. B. Adams). Describes 
procedure and gives results obtained in measuring 
d-c power available for RCM in B-17 and B-2/ 
aircraft. The data indicate that operation of APT-4 
transmitter does not constitute an excessive drain 
on the power system of either type of aircraft. 

(May 7, 1945) 


458 


APPENDIX 


1045-MR4 (L. B. Lusted) . Describes the installa- 
tion of 17- to 8Ji.-mc receiving and recording equip- 
ment in four P-38 “Droopsnoot” aircraft used for 
special investigations. 

(September 28, 1944) 

1045-MR8 (J. W. Keuffel). Describes the instal- 
lation of Jackal (new XA-2 model) in B-24 aircraft 
of 36th Squadron. Two were put in each aircraft, 
one on each side, in order to reduce the number of 
abortions due to equipment failure. 

(May 24, 1945) 

1045-MR12 (J. M. Hollywood, P. M. Keeler). 
Discusses the theory and practice of designing a 
harrage-jamming screen against German EW radar. 
Computations indicate the watts per megacycle that 
should be delivered to the antennas and charts show 
this quantity as a function of screening depth for a 
given distance of screen from the enemy radars. 
Examples are given for figuring the necessary air- 
craft installations and dispositions. For instance it 
is found that an 80-mile front can be screened by 
6 B-24’s each equipped with 25 APT-1 transmitters. 
Practical details are given for such an installation 
using one antenna for each two transmitters. 

(May 30, 1945) 

1045-MR14 (C. B. Clark). Summarizes the work 
done in making and testing a Ferret installation in 
a B-24J aircraft for the 8th Air Force to use in 
checking a jamming screen. The installation in- 
cludes antennas and antenna switches, racks and 
cables for two receivers, and two APA-11 pulse 
analyzers, remote indicator for magnesyn compass 
and the required inverters, starting switches, relays, 
and control boxes. 

(May 28, 1945) 

1045-MR15 (RP-987) (R. S. OHrien). A com- 
prehensive compilation of postwar information on 
the effectiveness of ROM against German flak 
radar. Extensive interrogations and inspections in- 
dicate that RCM, particularly simultaneous Win- 
dow and Carpet jamming, reduced the effectiveness 
of flak to one-fourth the value obtained with no 
jamming under blind conditions. RCM compelled 
optical fire direction to be used even under adverse 
conditions. Fully half the German h-f research per- 
sonnel were working on AJ devices involving a 
frenzied patching of old equipment. World War II 
was over before any appreciable number of 9-cm 
GL and AI equipments could be placed in service. 
The German radar status at the end of the war was 
about the same as that in the Allied laboratories 
about 1942. 

(June 16, 1945) 

411-44 (X-100) (F. E. Terman, W. D. White). 


Discussion of various factors affecting the distance 
from a radar system for which a jammer-equipped 
bomber is self-screened leads to the formula (when 
ground effects are neglected) 

where 

R = minimum distance (in miles) for effective 
jamming, 

Pt — effective peak power of radar transmitter, 

— power gain of radar transmitter antenna rela- 
tive to isotropic radiator, free-space condi- 
tions, in the direction of the target, 

Ag = echoing area of airplane or target in square 
meters, 

C — camouflage factor for type A or plan-position 
indicator presentation {includes pulse length 
and repetition rate) , 

B = receiver bandwidth (in megacycles) ahead of 
2nd detector, 

Pj — jamming noise power per megacycle of band- 
width, 

Gj.zn power gain of jamming antenna relative to 
isotropic radiator in direction of radar. 

Besides considering and evaluating each of these 
factors, the report presents graphs and tables of the 
calculated effectiveness of Mandrel, Dina, Carpet, 
Rug, Carpet Sweeper, and High-Power Carpet with 
respect to Freya, Hoardings, Wurzburg, and Japa- 
nese systems. There is also a short discussion on the 
screening of a group of aircraft. 

411-48 (X-402) (H. A. Chinn). A chart of tenta- 
tive data on the charactenst'ics of enemy radar 
equipment. 

411-93 (G-700, RP-186) (T. S. Kuhn, P. Sutro). 
Formulates a theory for approximate calculation of 
the power density of radar echoes from naval tar- 
gets and the computation of jamming powers and 
minimum jamming distances within the radar hori- 
zon. Values for minimum jamming distances are 
obtained graphically in connection with formulas. 
For low-power jammers the antennas should be 
placed as high as possible, whereas lower heights 
provide maximum effectiveness for high -power jam- 
mers. 

411-TM-106 (G-700, RP-299) (T. S. Kuhn). 
Preliminary report on expected size of echoes from 
naval targets, operational effectiveness of available 
jammers, and power requirements for proposed 
jammers. 

411-157 (G-704, RP-209) (M. Hamermesh). Ap- 
plies data on 100-mc measurements of radar cross 



nt 


RCM APPLICATIONS 


459 


sections of aircraft models to determination of 
cross-sectional areas giving maximum range for 
early warning and susceptibility to GL. The meas- 
ured data are averaged over a cone of small solid 
angles to allow for the small aspect variations of a 
plane in flight. Effective area is found to depend not 
only on the type of aircraft and its aspect, but also 
upon the radar frequency and polarization. Values 
are tabulated for B-24 and B-17E aircraft, singly 
and in formation, at various azimuths Avith vertical 
and horizontal polarizations. The discussion also 
covers anticipated results from future measure- 
ments on 500 me and their application to the Wurz- 
burg radar, the general conclusion being that there 
will be a decrease in the dependence of cross section 
on polarization. 

411-157A (G-704, RP-299) (A. T. Goble, M. 
Hamermesh, E. Presly) . Presents data on measure- 
ments of radar cross sections of aircraft models. 
The data are plotted as a function of aspect for 
B-29 at 75 and 225 me, TBM at 200 me, B-17 and 
B-24 at 450 me, and A-20 at 600 me. The graphs are 
to be used in solving operational problems on the 
design of jamming antennas, analysis of flak risk, 
evaluating the screening effectiveness of Window 
at various concentrations, etc., as illustrated by a 
few typical examples. 

411-251 (G-2700, RP-299) (D. A. Park, R. D. 
Sard) . Surveys the problem of predicting the effec- 
tiveness of jammers against GL and SLC radars. It 
is concluded that allowances should be made for 
variation of airplane cross section with aspect and 
for deviation of practical jamming signals from 
pure undipped noise. The computation procedure 
is (1) to plot a jamming map (based on experi- 
mentally determined characteristics of a specific 
type of radar and jammer, particularly the an- 
tenna) and (2) to determine the operational effec- 
tiveness of the given pattern by translating it into 
a map showing regions where guns can shoot most 
accurately or where searchlights are most dan- 
gerous. The chance of a hit under given tactical 
conditions is then found graphically and compared 
with the chance of a hit in the absence of jamming 
so as to give a numerical measure of effectiveness. 
This figure gives a good measure of the relative 
merits of different jamming transmitters and an- 
tennas against different radars. 

411-224 (G-1800, RP-406C) (R. Weinstock). 
Discusses the use of airborne corner reflectors for 
misdirection of lohed GL radar to protect bombers 
from flak. From graphs of calculated sizes of re- 
flectors necessary to modulate the target echo at the 
enemy’s lobe-switching rate it is concluded that the 


reflectors would have to be too large for practical 
use against 75-mc and 200-mc radars. The report 
concludes that reasonably small corner reflectors 
would be useful against microwave radar systems. 

411-228 (S-1800X, RP-474) (M. Hamermesh, 
R. Weinstock). Calculates RCM to nullify blind 
bombing effectiveness of British HoS Mark II in 
the 3,280- to 3,440-mc band and of AN/APQ-13 
and AN/APS-I5 radars in the 9,375 it 40-mc band. 
The estimates indicate that screening 1 sq mile of 
“city” from HoS requires at least 180 corner re- 
flectors with 3-m edges, from AN/ equipment at 
least 450 corner reflectors with 2-m edges, and from 
either type of equipment a prohibitive amount of 
Chaff. The use of ground-based c-w jammers is 
found to be more feasible, requiring a beam power 
(product of power by antenna gain) per megacycle 
of about 5 w against H 2 S, 24 w against APQ-13, 
and 55 w against APS-15. An area of about 12 sq 
miles can be screened against a single H 2 S by 16 
jammers and against a single APQ-13 or APS-15 
by 32 jammers. Brief consideration of covering an 
area of several square miles with the radiation from 
a pulsed jammer suggests the possibility of effective 
screening Avhen the peak power of the transmitter is 
equal to that of the enemy radar. 

411-129 (G-2400, RP-258) (L. R. Roller) . Con- 
cludes from experimental observations that radar 
echoes from naval spoofs (seaborne corner reflec- 
tors) cannot be distinguished, by A-scope observa- 
tion on any single radar system, from echoes due 
to warships. In both cases the fluctuations of the 
echoes are random in amplitude and in frequency. 
From observations with a 700-mc and a 3,000-mc 
radar system, for which the difference in response 
is approximately 12 db, it is concluded that the use 
of two systems of widely different frequency should 
provide a feasible means for distinguishing spoofs 
from ships. Further tests are to be made with fre- 
quency modulation of a pulsed radar system as a 
discriminating method. Further experiments on air- 
borne corners are necessary before an adequate con- 
clusion can be reached. 

411-188 (E-2400, RP-406J) (E. R. Brill, R. H. 
Hoglund) . Considers methods for discrimination 
between radar echoes from naval vessels and de- 
coys. The methods are based upon a theoretical 
analysis of the difference in reflection from a point 
source (for a decoy) and from a multipoint source 
(for a vessel) . The analysis predicts that the scope 
indication of the echo pulse due to a vessel will 
(1) be the more greatly distorted in shape and (2) 
show a greater variation in amplitude for small 
change in transmitter frequency. Experimental veri- 


460 


APPENDIX 


fication of (1) was obtained by modifying a search 
radar to provide a 3- to 6-mc i-f bandwidth, a 1.5- 
to 3-mc video bandwidth, and a delayed A scope 
expanded to between 100 and 200 yd per inch. Veri- 
fication of (2 ) was obtained by means of a mechani- 
cal f-m attachment to produce a 2-mc transmitter 
frequency deviation at a low audio rate. Neither of 
these modifications impair normal performance. The 
first is simpler and preferable for immediate appli- 
cation to present types of search radars to be used 
in identifying decoys. 

411-95 (Z-3000) (R. D. Sard). Summarizes facts 
known about German radar systems from the ROM 
viewpoint. Equipments and methods used for air 
defense and offense, naval radar, and IFF are de- 
scribed and discussed with respect to their vulner- 
ability to countermeasures. The air defense systems 
include (1) search sets giving range and bearing: 
Freya, Chimney, and Hoarding; (2) tracking sets 
giving elevation, bearing, and range: Small and 
Giant Wurzburgs for planes and for ships, (3) 
aircraft-interception Lichenstein (Fuge-202). The 
air offense systems include the bomber tail warning 
sets Fuge-214 and Fuge-216 and the aircraft-to- 
surface-vessel sets Fuge-200 and Fuge-213. Naval 
radar is considered under (1) land-based surface 
watching sets, (2) U-boat sets FuMO-30, FuMOGl, 
and Fuge-200U, (3) ship-borne radar. The IFF sets 
described are the Fuge-25a and Fuge-25. The more 
important systems are illustrated by sketches. The 
survey indicates absence of microwave equipment 
and lack of equipment for navigation and blind 
bombing. 

411-99 (G-1800, RP-406) (R. Weinstock). Sug- 
gests a method for shielding surfaced submarines 
from radar detection. Based on the results of mathe- 
matical analysis, the report finds that approxi- 
mately bell-shaped wire mesh screens will shield 
the conning tower and other objects on deck and 
that a downwardly curved screen will shield the 
above-water portion of the hull from ship-based or 
airborne radars. The screens should be so arranged 
as to provide no specular echo and to minimize the 
nonspecular (diffracted) return by having the upper 
and lower edges of the screens horizontal or extend- 
ing into the sea surface. Numerical comparison of 
echo values from noncamouflaged and from shielded 
submarines shows that shielding causes an appre- 
ciable reduction in the maximum range of radar 
detection. 

411-133 (Z-5000, RP-169) (W. D. White). Sum- 
marizes the results of a study of power requirements 
for shipboard 10-cm jammers. Calculations based 
upon an analysis of experimental data are presented 


in the form of curves showing the optimum jammer 
antenna height and the beam power (transmitter 
power less transmission line loss times antenna 
gain) required to screen the broadside aspect of a 
destroyer, light cruiser, and battleship. Another 
curve shows the percentage increase in beam power 
necessary with nonoptimum antenna heights. The 
general conclusion is that present available jam- 
ming equipment and techniques are adequate, pro- 
vided that the countermeasures operator has satis- 
factory means for quickly setting his transmitter 
on frequency. 

411-141 (L-1400, RP-406) (D. R. Scheuch). 
Describes a modified ASC-1 for operation with dual 
polarization. The simultaneous presentation by L 
scope directly compares the relative amplitudes of 
vertically and horizontally polarized received sig- 
nals, thus providing a specific means for testing the 
response of microwave confusion reflectors to both 
polarizations. Modifications comprise replacement 
of the original antenna system by the rotating 
antenna and parabolic reflector unit of an APG-1 
automatic GL set and the addition of a video 
switching unit and power supply, an L scope and 
power supplies, a junction box and an antenna 
sector-scan permitting PPI search operation up to 
180 degrees in azimuth. The equipment is installed 
in a light truck with trailer for operation in transit. 
The report gives a detailed illustrated description 
of the modified system with schematic diagrams of 
the added equipment. 

411-140 (G-509, RP-103) (F. Bloch, M. Hamer- 
mesh). Analyzes the effectiveness of countermeas- 
ures by means of the mathematical theory of 
probability. Equations are given for obtaining a 
quantitative estimate and procedures are described 
for judging the significance of the result. The gen- 
eral method of solving a problem is to compare the 
observed results with what might be expected if the 
countermeasure were completely ineffective. 

411-122 (L-1003, RP-XX) (F. P. Cowan). Out- 
lines requirements for spot-frequency jamming in 
the 100- to 1,000-mc range and in the 10-cm region, 
as found from experience in AJ field tests. The 
treatment covers transmitters, antennas, and re- 
ceivers for search, setting on, and monitoring, with 
recommended installation and operating procedures. 
Emphasis is placed on the advantages of corner 
reflector transmitting antennas and on the use of 
APA-6 pulse analyzer with APR-4 receiver for 
setting on and monitoring. Recommendations in- 
clude adequate shielding of the receiver and both 
antennas in order to isolate the receiver from the 
transmitter. The report includes descriptions of two 


RCM APPLICATIONS 


461 


ship-borne 100- to 1,000-mc installations meeting 
these requirements and of a 10-cm jamming instal- 
lation using beacon antennas and a spectrum 
analyzer. 

411-226 (S-1300, RP-459) (J. J. Ayittkopf). 
Gives the results of airborne jamming tests against 
AI radars. The tests were intended to aid in the 
development of tactics to facilitate the escape of a 
pursued aircraft. The report concludes that evasive 
action without jamming is not dependable. Escape 
is probable when continuous jamming is powerful 
enough to so overload the radar receiver that it is 
impossible to DF on the jamming signal. Because 
Window is so easily recognized, its use alone is not 
dependable, whereas it has good possibilities when 
used with jamming. 

411-245 (E/L-2800, RP-411) (R. H. Hoglund, 
F. P. Cowan). Outlines plans for field tests of the 
vulnerability of AN/ APS-/ radar to j amming with 
E-3200 test transmitter (see 411-256 in Section 5.2) 
operating in the X band. This project was sched- 
uled for transfer to the Navy when RRL terminated. 
Tests were also to be made of various AJ modifica- 
tions of the APS-4 receiver, including an FTC 
coupling circuit and a grid-bias type of gain con- 
trol. A special camera mechanism for photographing 
the scope images is described. 

411-250 (E/F6010, RP-338) (R. L. Henkel, T. S. 
Kuhn, L. B. Lusted, R. E. Reid). Describes a 
method for the measurement of jamming effective- 
ness and applies the method to a comparison of 
jamming transmitters and to the solution of opera- 
tional screening problems. The method requires ex- 
perimental operation of a flexible synthetic radar 
to supply data for plotted curves showing the effec- 
tiveness of a jammer operating into a receiver. The 


curves delineate minimum observable steady pulse 
as a function of receiver frequency. (See 411-251.) 
Quantitative results for 200 me are given for APT-4, 
APT-1, APQ-2, and a test transmitter 'when they 
were operating into APR-1, APR-4, and RDO. The 
tests indicated the marked superiority of APT-4 
with respect to the magnitude of the signal and the 
frequency band over which it will screen. The re- 
sults differ greatly from and are more reliable than 
those predicted by the “accepted power” theory of 
jamming. 

411-278 (W-200, RP-299) (J. F. Youngblood, 
B. M. Kuck). Points out the faults in various ex- 
perimental methods for finding the formation factor 
or ratio of effective echoing area of n planes to that 
of a single plane when observed at the same aspect. 
This factor is used in estimating the number of 
planes in a formation and in calculating the jammer 
power necessary to shield a specified formation. The 
report concludes that a fairly satisfactory practical 
method is to obtain the average amplitude of a 
number of pulses and to record the instant when 
a predetermined level is reached. A proposed instru- 
ment for doing this is described in 411-257. 

411-257 (W-200, RP-299) (R. K. Vermillion). 
Describes the P-102 instrument to be used with the 
SCR-545 or other radar in measuring the formation 
factor of aircraft. The instrument is essentially a 
constant-speed tape recorder which is marked by 
two sets of positive pulses. One set consists merely 
of time-reference pulses of either 0.1- or 1-psec 
intervals. The other set is produced by adding a 
series of from 5 to 50 video signals from the radar 
receiver (slightly modified) to provide high enough 
voltage to trip a trigger circuit, and thus produce a 
series of pulses. These are interpreted as explained 
in 411-278. 







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GLOSSARY 


AA. Antiaircraft. 

ABL-15. American British Laboratory of NDRC Division 15. 

A-c. Alternating-current (adj.). 

ADRDE. Air Defense Research and Development Estab- 
lishment (Br. Army). (Later changed to RRDE — Radio 
Research and Development Establishment.) 

A-F. Audio-frequency (adj.). 

AFC. Automatic frequency control. 

AI. Aircraft interception (airborne radar for plane-to-plane 
detection). 

AIL. Airborne Instruments Laboratory. 

AJ. Antijamming. 

Alsos. a scientific mission sent to Germany immediately 
after World War II under the auspices of OSS with the 
purpose of gathering information on scientific subjects in 
enemy countries, particularly from scientific sources. 

AM. Amplitude modulation (noun). 

A-M. Amplitude-modulated (adj.). 

AN. Army-Navy. 

Angel. An electromagnetic-wave reflector (usually a 
metallic corner reflector) used to create radar echoes for 
deception and confusion purposes. 

ASB. A Navy airborne vs. surface target radar. 

Ascope. a radar indicator on which signals corresponding to 
targets appear as vertical deflections on a horizontal-range 
trace. 

A.S.E. Admiralty Signal Establishment (Br. Navy). 

ASV. Air-to-surface vessel — airborne radar for detecting 
seaborne targets. 

Automat. An automatic jamming system. 

A VC. Automatic-volume-control. 

Bagful. A British receiver for use in examining in detail any 
particular band. Has a tape recorder that lasts for 8 hours. 
Covers frequency band of 300-400 Me; 380-500 Me; and 
480-610 Me. 

Bagpipes. A type of communication jamming modulation 
which sounds like the playing of bagpipes. 

Barrage Jamming. The simultaneous jamming of a num- 
ber of adjacent channels or frequencies. 

Beagle. An automatic search jammer. 

Beaver. Ground-based radar search DF and jamming 
mission of which there were 4. All involved the 1st Signal 
Service Platoon (Special). 

Beechnut. A ground-to-aircraft communications system 
employing two-tone keying. 

Benito. German aircraft navigation system operating in the 
40-Mc band. Provides indications of azimuth and range. 

Big Ben. Code name given to the German V2 rocket. 

Birdnesting. Formation of tangled clusters of chaff during 
Window operations, resulting in poor dispersal and conse- 
quent low reflection efficiency. 

Blanket. A system of direction-finding deception. 

Boozer. An airborne warning receiver that intercepts and 
distinguishes between German ground-controlled intercep- 
tion, GL, and AI transmissions. 

Broadloom (CXFR). 500-mc jamming transmitters using 
tunable magnetrons. 


Broom. An automatic search jammer. 

Bscope. a type of radar indicator, presenting range versus 
azimuth angle, in rectangular coordinates. 

BTL. Bell Telephone Laboratories. 

CAAC. Countermeasures Air Analysis Center, AAFPOA. 

Carpet. Airborne, noise-modulated, barrage-jamming trans- 
mitter. 

Catalina. Navy PBY Flying Patrol Boat. 

CBS. Columbia Broadcasting System. 

CH. Chain-Home, code word for system of low frequency 
radars installed by British in 1938 along their own coast. 

Chaff. Electromagnetic-wave reflectors in the form of 
narrow metallic strips approximately one-half wave length 
long used for creating radar echoes for confusion purposes. 

CHI. Generic designation for type of Jap radar. 

Chick. An expendable jammer. 

CIC. Combat Information Center. 

Cigar. A large ground-based communications jammer. 

CiNCPAC. Commander-in-chief Pacific. 

Confuser. a mechanical noise generator. 

Corner Reflector. An electromagnetic-wave reflector con- 
sisting of three intersecting, mutually perpendicular, plane 
metallic surfaces. 

Curtain. Airborne VHF homing equipment designed for 
use against German VHF. 

CV. Aircraft carrier. 

CVL. Light Aircraft carrier. 

c-w. Continuous- wave (adj.). 

D-c. Direct-current (adj.). 

DF. Direction finding (noun). 

DINA. Direct-noise amplifier. This is a code name given to a 
series of transmitters supplying random-noise output with- 
out a carrier frequency. 

Dinamate. a DINA transmitter plus a receiver (MATE). 
When the latter is tuned to a signal to be jammed, the 
former is automatically tuned to the same frequency. 

Electra. German 200-500 Me multi-lobe Lorenz system 
(a bomber navigational aid). 

Elephant. A very complete shipborne jamming system. 

Elmer. A communications deception device designed to 
permit a single station to emit signals simulating an Army 
net. 

EW. Early warning. 

Earns. Farnsworth Telephone and Radio Corporation. 

FD. The Mark IV Navy fire-control radar. 

FEAF. Far East Air Forces. 

Ferret. An aircraft carrying a large amount of radio- 
countermeasures investigational equipment. 

Fishline. Same as Tinsel Rope. 

Flute. A type of magnetron. 

FM. Frequency modulation (noun). 

F-M. Frequency-modulated (adj.). 

Freya. 120-Mc German early-warning ground radar equip- 
ment; modified to cover 75-100 Me and 120-180 Me. 

FT&R. Federal Telephone & Radio Corporation. 

Fuge FuGe. (Followed by type No.) German radio or 
radar (Funkgerat or Funk messergerat). 


463 


464 


GLOSSARY 


Gastox. An audio noise generator. 

GCI. Ground-controlled interception — the direction, from 
the ground, of friendly fighters with the objective of inter- 
cepting enemy planes. Instructions are based on data ob- 
tained by radar. 

GE. General Electric Company. 

George Box. An early-warning radar antijamming attach- 
ment. 

GL. Gun-laying-radar used to direct gunfire. 

GM. Guided missiles. 

Goldammer. Same as Stendal B. 

GR. General Radio Company. 

GSI. Geophysical Services, Inc. 

Gulls. Confusion reflector. 

H-Dienst. German listening service for plotting Allied air- 
craft by their radio transmissions. 

H2S. British high-altitude-bombing radar device — 10 cm 
(early form), 3 cm (later form). Scope gives presentation of 
land flown over. 

H2X. An American type of radar high-altitude-bombing 
device — 3 cm. 

Hoardings. German early-warning radar, also called Mam- 
mut, in frequency range 123 to 128 Me. 

i-F. Intermediate-frequency (adj.). 

IFF. Identification Friend or Foe. System of radio interroga- 
tion and reply (if friendly) generally used in connection 
with radar for identifying aircraft. 

IT&T. International Telephone & Telegraph Co. 

Jackal. An airborne, frequency-modulated, barrage-jammer 
for communications channels. 

Jagdschloss. 150-Mc GCI with continuously rotating array 
and PPL A ground radar equipment. 

JAN. Joint Army-Navy. 

J&B. Jansky & Bailey. 

JNW. Joint New Weapons Committee of Joint Chiefs of 
Staff. 

Jostle. British, airborne, barrage jammer for use against 
German tank and paratroop communications. 

J/S. Jam-to-signal (ratio). 

K Band. 11,000 to 33,000 Me. 

Kites. Airborne, self-opening, and free-falling corner re- 
flectors (same as Angels). 

Knickebeine. (Headache) German 30-33 Me long-range 
Lorenz beam system for blind bombing, using intersecting 
beams to mark the target. (A bomber navigational aid.) 

LAB. Low-altitude-bombing attachment for SCR-717-B and 
AN/APQ-13 equipped planes. 

L Band. 390 to 1,550 Me. 

LC. Inductance capacitance. 

Listening-Through. Observation of a signal being jammed 
through the jamming. 

Loran. Long-range radio-navigation system. 

Lorenz. German firm. It built a 600-Mc radar designed for 
GL but relegated to coast watching (ground radar equip- 
ment). 

Mandrel. Airborne, noise-modulated, barrage-jamming 
transmitter primarily for the 85- to 135 Me region, (e.g., 
AN/APT-3). 

Meaconing. The destruction of the accuracy of a radio- 
navigated system by deceptive transmissions designed to 
imitate actual radio-navigational aid signals. 


Moonshine. A pulse-repeating system designed to conceal 
the magnitude and extent of a radar target. 

NDRC. National Defense Research Committee. 

Neptune. Code word for Naval Port of Normandy Invasion. 
(Also Neptun Gerat — German AI and tail-warning radar in 
frequency range 150 to 182 Me.) 

NRL. Naval Research Laboratory. 

OCSigO. Office of the Chief Signal Officer. 

OSRD. Office of Scientific Research and Development. 

OSURF. Ohio State University Research Foundation. 

OTC. Officer in Tactical Command. 

PAD. A noncoherent-pulse jammer. 

Panther. A panoramic receiver. 

Perfectos. Airborne radar equipment designed to trigger 
the German IFF, thus measuring range to and permitting 
homing on German fighter formations. 

Peter. A pulse-repeating system for confusing angular 
definition of radar sets. 

Peter Pan. A signal-repeating jamming system. 

Petticoat. Mission to install RCM equipment in British 
Naval vessels for use in Normandy invasion. 

PF. Proximity fuze. 

Piano. A signal-repeating jammer. 

Piccolo. A type of magnetron. 

Pickets. Small vessels usually disposed to give advance 
warning of enemy activity. 

Pimpernel. An automatic receiver and drive unit for setting 
jamming transmitters to frequency. 

Ping Pong. Accurate British DF system used to determine 
coastal radar locations. 

Porcupines. B-29 with barrage-jamming installation for 70 
to 200 Me. The numerous stub antennas gave plane appear- 
ance of a porcupine. 

PPL Plan-position indicator. Indicator for radar providing 
polar-coordinate presentation of azimuth and range. 

PRC. Panoramic Radio Corporation. 

PRF. Pulse-repetition frequency. 

Quado. a jamming frequency alignment indicator. 

RC. Resistance capacitance. 

RCA. Radio Corporation of America. 

RCM. Radio countermeasures. 

R-F. Radio-frequency (adj.). 

RHB. Radar homing bomb. 

RI. Radio intercept. 

RL. Radiation Laboratory at the Massachusetts Institute 
of Technology. 

Rope. Electromagnetic-wave reflectors, for the creation of 
artificial radar echoes, in the form of a long (about 400 ft) 
metallic ribbon. 

RRL. Radio Research Laboratory. 

RT. Radio Telephone (British Term). 

Ruffian. German navigational system operating on 66.5- 
70 Me using three stations. Gives bomber the ground speed 
when 15 kilometers from his target and sounds a horn at the 
bomb release point on the target. It is a grid of “coarse” and 
“fine” beams over the target area. 

Rug. An airborne low-powered radar jammer for use jn the 
frequency range 180-450 Me. , ^ 

Sambo. The detection of propeller modulation and attempt 
to use it as identification, particularly by coating one or 
more propeller blades with nonreflecting material. 


GLOSSARY 


465 


S Band. 1,550 to 5,200 Me. 

SE. S band radar for installation on surface craft for the 
detection of surface craft. 

Seetakt. 350-380-Mc Freya-type coast watcher. Also called 
Calais Anlage. A ground radar equipment. 

Setting-On. Alignment of the frequency of a jamming trans- 
mitter with the frequency of a signal to be jammed. 

Shoran. a “line of sight” precision bombing system (in the 
300-Mc band) which employs two ground stations and an 
airborne transmitter and receiver with computer. 

SLC. Searchlight control (radar used for aiming search- 
lights). 

Spot Jamming. The jamming of a specific channel or fre- 
quency. 

Stendal B. a German antijamming device. 

Stopwatch. An automatic jammer alignment system. 

Tail. Attachment to permit homing on jammer or radar 
signals. 

TBF. Type of torpedo bomber (Grumman). 

TBM. Type of torpedo bomber (Martin). 

Tea. a shipborne jamming transmitter for use against 
guided missiles. 

Tinsel. Conversion of existing transmitters to jammers by 
providing source of noise for modulation purposes (British 
term). 

Tinsel Rope. Tuned rope made from tinsel. 


TRE. Telecommunications Research Establishment (UK). 

Tuba. A 50-kw ground-based jammer used against German 
A I radar. 

Turnstiles. Confusion reflectors made from three half- 
wave dipoles of wire held mutually perpendicular at the 
centers. 

U-H-F. Ultrahigh-frequency. 

VB. Dive bomber. 

V-E. Victory in Europe. 

V-H-F. Very-high-frequency. 

V-J. Victory in Japan. 

VoFLAG. A two-tone six-element error-proof code system for 
a teleprinter communication. 

VT. Torpedo bombers. 

WE. Western Electric Company. 

WEST. Westinghouse Electric & Manufacturing Company. 

Whip. Antenna. 

Window. The use of Chaff, Angels, or other reflectors for 
radar confusion purposes. 

Wurzburg. German radar tracking sets used for ground- 
controlled interception, searchlight control, and gun-laying 
in frequency range 520 to 590 Me. 

WuRZLAUS. German AJ device. Coherent pulse system for 
discriminating between slowly moving Window echoes and 
aircraft echoes. 

X Band. 5,200 to 11,000 Me. 



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BIBLIOGRAPHY 


Division 15 technical reports are numbered in accordance with a simple system. The report number consists of two 
parts; the first part is the OEMsr contract number and the second part is a serial number, assigned consecutively by each 
contractor. Thus the first report issued by the laboratory operating under Contract OEMsr-867 would be Report 867-1. 
The second report from this laboratory would be 867-2, etc. 

A few laboratories issued technical memoranda, in addition to technical reports. These were numbered in accordance 
with the same system except that the letters “TM” preceded the serial number. Thus the fourteenth technical memorandum 
issued by the laboratory operating under Contract OEMsr-411 would be numbered 411-TM-14. 

Abstracts of the Division 15 Technical Reports listed in the following bibliography are given in the Appendix. Since 
report titles are sometimes not altogether descriptive, reference to these abstracts is recommended. 

Numbers such as Div. 15-402. 4-Ml indicate that the document listed has been microfilmed and that its title appears in 
the microfilm index printed in a separate volume. For access to the index volume and to the microfilm, consult the Army 
or Navy agency listed on the reverse of the half-title page. 


1 . Developmental Model of an Interference Generator for the 
2 to 20 Me Spectrum, Madison Cawein, Report 89-1, 
Projects NDRC-58, C-25, and SC- 19, Farnsworth Tele- 
vision and Radio Corporation, Nov. 16, 1941. 

Div. 15-402.4-Ml 

2. Preliminary Instructions for Interference Generator 
NDRP 58, Report 89-2, Projects C-25 and SC-19, 
Farnsworth Television and Radio Corporation. 

Div. 15-402.4-M3 

3. Progress Report 1, Madison Cawein, Report 89-3, Farns- 
worth Television and Radio Corporation, July 31, 1941. 

Div. 15-130-Ml 

4. Progress Report 2, Madison Cawein, Report 89-4, Farns- 
worth Television and Radio Corporation, Sept. 3, 1941. 

Div. 15-130-Ml 

5. Progress Report 3, Madison Cawein, Report 89-5, Farns- 
worth Television and Radio Corporation, Oct. 3, 1941. 

Div. 15-130-Ml 

6. Progress Report 4, Madison Cawein, Report 89-6, Farns- 
worth Television and Radio Corporation, Dec. 4, 1941. 

Div. 15-130-Ml 

7. Status Memo: NDRC 58, Report 89-7, Farnsworth 
Television and Radio Corporation, Jan. 21, 1942. 

Div. 15-130-M2 

8. Progress Report 5, Madison Cawein, Report 89-8, Farns- 
worth Television and Radio Corporation, Feb. 5, 1942. 

Div. 15-130-Ml 

9. Antenna Patterns for Aircraft, George Sinclair, NDCrc- 

100, The Ohio State University Research Foundation, 
Aug. 31, 1942. Div. 15-331. 1-Ml 

10. A Method for Determining Tank Antenna Patterns, 
George Sinclair, NDCrc-100, The Ohio State University 
Research Foundation, Sept. 24, 1942. 

Div. 15-332. 3-Ml 

11. C-11 Antenna Patterns for Aircraft, George Sinclair, 

NDCrc-100, The Ohio State University Research Foun- 
dation, Aug. 24, 1943. Div. 15-333.2 1-M5 

12. Effects of the Airplane Structure on the Polarization of 

Airborne Antennas, George Sinclair and E. C. Jordan, 
NDCrc-100, The Ohio State University Research Foun- 
dation, Nov. 17, 1943. Div. 15-333. 3-Ml 

13. Modeling the Direction Finding Loop Antenna: Applica- 

tion to a Model of a B-24 Aircraft, Wayne E. Rife, 
NDCrc- 100-3, Projects RP-404 and AC-297.04, The 
Ohio State University Research Foundation, June 11, 
1945. Div. 15-331. 13-M3 


14. Final Report on Contract NDCrc-100, George Sinclair 
and Wayne E. Rife, NDCrc- 100-4, Report 759, Projects 
RP-399, RP-404, and SC- 17, The Ohio State University 
Research Foundation, Oct. 30, 1945. Div. 15-140-Ml 

15. Developmental Model of an Interference Generator for the 
15 to 30 Me Spectrum, Albert Preisman, Report 285-1, 
Projects C-26 and SC-19, International Telephone and 
Radio Laboratories, June 19, 1942. 

Div. 15-401.4-M3 

16. Type NLS 518 Interference Generator, Report 285-2, 

Project C-26, International Telephone and Radio Labo- 
ratories, Feb. 17, 1942. Div. 15-401. 4-Ml 

17. Memorandum on the Interference Generator, Albert Preis- 
man, Report 285-3, International Telephone and Radio 
Laboratories, June 19, 1942. 

Div. 15-401.4-M2 

18. Tests of Effect of Interference on Radio Telegraph Recep- 

tion, D. K. Gannett, Report 626-1, Western Electric 
Company, May 27, 1942. Div. 15-21 1.321-Ml 

19. Effect of Resistance Noise on Intelligibility of Telegraph 
Signals and Speech, D. K. Gannett, Report 626-2, 
Western Electric Company, June 2, 1942. 

Div. 15-21 1.321-M2 

20. Effectiveness of Various Audio Frequency Noises in Mask- 
ing Speech, D. K. Gannett, Report 626-3, Project C-56, 
Western Electric Company, Aug. 25, 1942. 

Div. 15-211.322-Ml 

21. Final Report on NDRC Project C-56 Study of Interference 
Generation, D. K. Gannett, Report 626-4, Western 
Electric Company, Sept. 22, 1942. 

Div. 15-211.322-M2 

22. Automatic Radar Jamming System, Pimpernel, P. C. 

Goldmark, Report 653-1, Columbia Broadcasting Sys- 
tem, June 2, 1943. Div. 15-41 1-Ml 

23. Resnatron Report, Report 747-1, Westinghouse Electric 
and Manufacturing Company, Mar. 1, 1943. 

Div. 15-342-Ml 

24. Development of Resnatrons for High Power CW Ground 

Jammer, W. B. Fretter and F. W. Boggs, Report 747-2, 
Projects RP-351-a, SC-94.24, and NS-394.03, Westing- 
house Electric and Manufacturing Company, Sept. 21, 
1944. Div. 15-342-M2 

25. Development of 10 KW Magnetrons, F. W. Boggs, Report 

747-3, Projects RP-351-a, SC-94.24, and NS-394.03, 
Westinghouse Electric and Manufacturing Company, 
July 5, 1945. Div. 15-341. 5-M3 


467 


468 


BIBLIOGRAPHY 


26. Note on the Patterns of Cone Antennas, George Sinclair, 

Report 759-1, The Ohio State University Research 
Foundation, Oct. 29, 1942. Div. 15-333. 21-Ml 

27. The Radiation Patterns of a Cone Antenna on a B-17E at 
250 Me, George Sinclair, Report 759-2, The Ohio State 
University Research Foundation, Nov. 22, 1942. 

Div. 15-333.21-M2 

28. Patterns of Cone Antennas on a B-24, George Sinclair, 
Report 759-3, The Ohio State University Research 
Foundation, Dec. 20, 1942. 

Div. 15-331. 112-Ml 

29. Patterns of a Dipole on a Type A T-11 for 110 Me, George 
Sinclair, Report 759-4, The Ohio State University Re- 
search Foundation, Dec. 28, 1942. 

Div. 15-331.12-Ml 

30. Patterns of Nose Antennas on the AT-11, George Sinclair, 

Report 759-5, The Ohio State University Research 
Foundation, Jan. 21, 1943. Div. 15-331. 111-Ml 

31. Patterns for a 50-ohm Cone Antenna Mounted on a Dise, 
George Sinclair, Report 759-6, The Ohio State Univer- 
sity Research Foundation, Jan. 23, 1943. 

Div. 15-333.21-M3 

32. The Patterns of an Antenna Array for the SCR- 5 87 on the 
B-17F, George Sinclair, Report 759-7, The Ohio State 
University Research Foundation, Feb. 20, 1943. 

Div. 15-331. 1-M2 

33. Antennas for the RC-164, George Sinclair, Report 759-8, 

The Ohio State University Research Foundation, Mar. 
17, 1943. Div. 15-331. 111-M2 

34. Note on the Patterns of Antennas for Gymnast, George 
Sinclair, Report 759-9, The Ohio State University Re- 
search Foundation, Mar. 25, 1943. 

Div. 15-331. 1-M3 

35. Antenna Patterns on the Hairy Butterfly, George Sinclair, 
Report 759-10, The Ohio State University Research 
Foundation, May 15, 1943. 

Div. 15-331. 1-M4 

36. Antenna Patterns on the Hairy Butterfly, Robert B. 
Jacques, Report 759-11, The Ohio State University 
Research Foundation, June 25, 1943. 

Div. 15-331. 1-M5 

37. Antenna Patterns of Special Loop on A-29 Lockheed 

Hudson Bomber, Robert B. Jacques, Report 759-12, The 
Ohio State University Research Foundation, July 24, 
1943. Div. 15-331. 13-Ml 

38. Antenna Patterns of Vertical Antennas on B-17 and B-24 

Bombers, Frequency 35 Me, Robert B. Jacques, Report 
759-13, The Ohio State University Research Founda- 
tion, Aug. 2, 1943. Div. 15-331. 15-Ml 

39. Antenna Patterns of a Short, Wide Band Antenna Fre- 

quency Range 200-500 Me, Robert B. Jacques, Report 
759-14, The Ohio State University Research Founda- 
tion, Aug. 2, 1943. Div. 15-333.21-M4 

40. A ngel at 515 Me Reflection Patterns, George Sinclair and 

Robert B. Jacques, Report 759-16, Project RP-269, The 
Ohio State University Research Foundation, Feb. 14, 
1944 Div. 15-241.31-Ml 

41. Angel at 360 Me Reflection Patterns, Robert B. Jacques, 
Report 759-17, Project RP-269, The Ohio State Uni- 
versity Research Foundation, Feb. 18, 1944. 

Div. 15-241. 31-M2 


42. Angel at 410 Me Reflection Patterns, Robert B. Jacques, 
Report 759-18, Project RP-269, The Ohio State Uni- 
versity Research Foundation, Feb. 20, 1944. 

Div. 15-241.31-M4 

43. Angel at 1000 Me Reflection Patterns, Robert B. Jacques, 
Report 759-19, Project RP-269, The Ohio State Uni- 
versity Research Foundation, Feb. 18, 1944. 

Div. 15-241.31-M3 

44. Antenna Radiation Patterns for the Albatross I Project, 

Ernest A. Jones and George Sinclair, Report 759-20, 
Project RP-137, The Ohio State University Research 
Foundation, Feb. 25, 1944. Div. 15-333. 21-M6 

45. B-24 Bomber at 100 Me Reflection Patterns, Robert B. 
Jacques, Report 759-21, Project RP-269, The Ohio 
State University Research Foundation, Mar. 18, 1944. 

Div. 15-822-Ml 

46. B-17E Bomber at 100 Me Reflection Patterns, Robert B. 
Jacques, Report 759-22, Project RP-269, The Ohio 
State University Research Foundation, Mar. 18, 1944. 

Div. 15-822-M2 

47. Antenna Radiation Patterns for the HS-293, Ernest A. 
Jones, Report 759-23, Project RP-137, The Ohio State 
University Research Foundation, June 20, 1944. 

Div. 15-333.21-M7 

48. A Square Root Amplifier, Eric W. Vaughan and Norman 
Kennedy, Report 759-24, The Ohio State University 
Research Foundation, May 29, 1944. 

Div. 15-521.3-M2 

49. Reflection Measurements on Wire Grids and Mesh Angels 
at 2000 and 3000 Me, George Sinclair and Robert B. 
Jacques, Report 759-25, Project RP-269, The Ohio 
State University Research Foundation, Aug. 16, 1944. 

Div. 15-241. 31-M5 

50. Summary of A ntenna Radiation Patterns for A ntennas on 
the PB4Y-2, Ernest A. Jones, Report 759-26, Projects 
RP-137 and NA-221, The Ohio State University Re- 
search Foundation, Sept. 10, 1945. 

Div. 15-333.21-Mll 

5 1 . Summary of A ntenna Radiation Patterns for A ntennas on 
the P4M, Ernest A. Jones, Report 159-21 , Projects 
RP-137 and NA-199, The Ohio State University Re- 
search Foundation, Sept. 1, 1945. 

Div. 15-333.21-M9 

52. Summary of Antenna Radiation Patterns for Ferret C-1, 

Ernest A. Jones, Report 759-28, Projects RP-137 and 
AC-259.06, The Ohio State University Research Foun- 
dation, Sept. 10, 1945. Div. 15-333. 21-M 12 

53. Antenna Radiation Patterns for 1,000 Me Measured on 
the SB2C, Ernest A. Jones, Report 759-29, Projects 
RP-137 and NA-221, The Ohio State University Re- 
search Foundation, Sept. 13, 1945. 

Div. 15-333.21-M13 

54. Reflection Measurements on Antireflective Target Tow 
Cable, Kenneth P. Yates and P. C. Wright, Report 
759-30, Project RP-269, The Ohio State University 
Research Foundation, Aug. 13, 1945. 

Div. 15-821-M2 

55. Modeling Slot Antennas, D. R. Rhodes and E. C. 
Jordan, Report 759-31, Project RP-137, The Ohio State 
University Research Foundation, Oct. 3, 1945. ' 

Div. 15-333.53-M2 


I/' 


BIBLIOGRAPHY 


469 


56. Measurement of Shipborne Antenna Patterns Using 

Models, Herman Heil, E. C. Jordan, and David Cleck- 
ner, Report 759-32, Projects RP-427 and NS-398.04, 
The Ohio State University Research Foundation, Oct. 
16, 1945. Div. 15-333.21-M14 

57. A Continuous-Wave Method of Measuring Radar Cross- 
Sections and Reflection Patterns by Means of Models, 
Kenneth P. Yates, Report 759-33, Projects RP-269, 
AN-8, and SC-96.01, The Ohio State University Re- 
search Foundation, Oct. 31, 1945. 

Div. 15-822. 1-M3 

58. Final Report on Contract OEMsr-759, George Sinclair, 

NDCrc-100, Report 759-34, Projects RP-399, RP-404, 
and SC- 17, The Ohio State University Research Foun- 
dation, Oct. 18, 1945. Div. 15-140-Ml 

59. Jamming Report on Propagation Study, W. C. Babcock, 

Report 778-1, Project C-63, Western Electric Company, 
Oct. 19, 1942. Div. 15-211. 1-Ml 

60. Conversion of Standard Radio Equipment to Jamming 
Equipment, M. E. Campbell, Report 778-2, Western 
Electric Company, Nov. 11, 1942. 

Div. 15-321.3-Ml 

61. Notes on the Effectiveness of FM Jamming Signals, M. E. 

Campbell, Report 778-3, Project C-63, Western Electric 
Company, Jan. 28, 1943. Div. 15-21 1.31-Ml 

62. Jamming Method of Solving Transmission Problems, 
A. C. Peterson, Report 778-4, Project C-63, Western 
Electric Company, Jan. 27, 1943. 

Div. 15-211. 1-M2 

63. A Study of Three Antennas, W. C. Babcock, Report 

778-5, Project C-63, Western Electric Company, Jan. 
26, 1943. Div. 15-332.18-Ml 

64. Jamming Notes Relative to a Type of Jamming Signal, 
A. D. Fowler and K. C. Black, Report 778-6, Project 
C-63, Western Electric Company, Jan. 29, 1943. 

Div. 15-211. 31-M2 

65. Vulnerability of Various Pulse Communication Methods 

to Resistance Noise, W. H. Wise and K. C. Black, Report 
778-7, Project C-63, Western Electric Company, Jan. 
30, 1943. Div. 15-21 1.323-Ml 

66. Voice Frequency Noise Generator, M. E. Campbell, Re- 
port 778-8, Project C-63, Western Electric Company, 

Jan. 30, 1943. Div. 15-343.21-Ml 

67. Study of Radio Jamming, K. C. Black, Report 778-9, 
Project C-63, Western Electric Company, Feb. 1, 1943. 

Div. 15-211. 1-M3 

68. Antenna System for Project Moth, Robert Serrell, Report 

867-1, Project RP-261, Columbia Broadcasting System, 
November 1943. Div. 15-331. 13-M2 

69. Pulsed Signal Generator, Paul S. Hendricks, Report 

867-2, Project RP-241, Columbia Broadcasting System, 
July 2, 1943. Div. 15-512-M3 

70. Ultra High Frequency Diode, Martin M. Freundlich, 

Report 867-3, Columbia Broadcasting System, Dec. 21, 
1943. Div. 15-346-Ml 

71. Pulse Generator, Paul S. Hendricks, Report 867-4, 

Project RP-241, Columbia Broadcasting System, Aug. 
5, 1943. Div. 15-512-M4 

72. Investigation of Long Wire Antennas, J. A. Nelson, 

Report 867-5, Project RP-261, Columbia Broadcasting 
System, Jan. 14, 1944. Div. 15-333. 1-M8 


73. The Use of Dark Trace Tubes for Integration, Martin M. 
Freundlich, Robert Serrell, and P. C. Goldmark, Report 
867-6, Columbia Broadcasting System, Dec. 16, 1943. 

Div. 15-314.22-Ml 

74. Stub Antennas with Series Matching Sections, Robert 
Serrell, Report 867-7, Project RP-261, Columbia Broad- 
casting System, April 1944. 

Div. 15-333.54-Ml 

75. UHF Power Meter, Orville J. Sather, Report 867-8, 

Project RP-261, Columbia Broadcasting System, April 
1944. Div. 15-521. 2-Ml 

76. Experimental Window Research, Robert Serrell, Edgar 

C. Hayden, and Bernard Erde, Report 867-9, Projects 
RP-406-G and SC-96.01, Columbia Broadcasting Sys- 
tem, February 1946. Div. 15-241-M8 

77. An Electromagnetic Model of the Ocean, Edgar C. Hay- 
den, Report 867-10, Project RP-261-B, Columbia 
Broadcasting System, February 1945. 

Div. 15-333.22-M4 

78. Final Technical Report Under Contract OEMsr-867, P. C. 

Goldmark, Report 867-11, Columbia Broadcasting 
System, February 1946. Div. 15-170-Ml 

79. The Sleeve Antenna and Use of Steel in Radiators, P. S. 

Carter, Report 895-1, Project RP-260, RCA Labora- 
tories, July 14, 1943. Div. 15-332. 28-Ml 

80. Report on Three Antennas, R. S. Wehner, Report 895-2, 
Project RP-260, RCA Laboratories, Aug. 9, 1943. 

Div. 15-332. 28-M2 

81. Power Limit — Airplane Antennas, P. S. Carter, Report 

895-3, Project RP-260, RCA Laboratories, Aug. 12, 
1943. Div. 15-333. 4-Ml 

82. Readability of FM, AM and Telegraph Systems, Murray 

C. Crosby, Report 895-4, Project RP-131, RCA Labora- 
tories, Aug. 24, 1943. Div. 15-21 1.1-M7 

83. Radio- Frequency Propagation Above the Earth's Surface, 

Paul F. Godley, Jr., Report 895-5, RCA Laboratories, 
Sept. 11, 1943. Div. 15-810-Ml 

84. Differentiating and Limiting Amplifier, Murray C. Cros- 

by, Report 895-6, Project RP-131, RCA Laboratories, 
Sept. 30, 1943. Div. 15-21 1.1-M8 

85. Performance Characteristics of Receiver SCR-587 / CP R- 
46AAO {ARC-1), Warren H. Bliss, Report 895-7, 
Project RP-131, RCA Laboratories, Oct. 22, 1943. 

Div. 15-31 1.111-Ml 

86. Monitoring and Tracking, W. A. Anderson, Report 

895-8, Project RP-263, RCA Laboratories, Oct. 26, 
1943. Div. 15-232-Ml 

87. Considerations Affecting Choice of Direction Finder De- 

ception Systems, H. O. Peterson and Warren H. Bliss, 
Report 895-9, Project RP-252, RCA Laboratories, Dec. 
16, 1943. Div. 15-313. 2-Ml 

88. Notes on Antenna Tests at Rocky Point Laboratory, P. S. 
Carter and R. S. Wehner, Report 895-10, Project 
RP-260, RCA Laboratories, Dec. 22, 1943. 

Div. 15-333.1-M7 

89. Antennas and Cylindrical Fuselage, P. S. Carter, Report 

895-11, Project RP-260, RCA Laboratories, Dec. 24, 
1943. Div. 15-333. 22-M2 

90. AJ Facsimile Transmission System, C. N. Gillespie 

Report 895-12, Project RP-228, RCA Laboratories, 

Jan. 12, 1944. Div. 15-212.13-Ml 


470 


BIBLIOGRAPHY 


91. AJ Characteristics of Printing Telegraph Systems, James 

A. Spencer, Report 895-13, Project RP-227, RCA 
Laboratories, Jan. 15, 1944. Div. 15-212.12-M3 

92. J and AJ Investigation of a Pulse Phase Modulation 

Communication System, John B. Atwood and Grant E. 
Hansell, Report 895-14, Project RP-123, RCA Labora- 
tories, Feb. 16, 1944. Div. 15-21 1.323-M2 

93. Notes on Synthesis of Broad-Band Matching Sections, 

R. S. Wehner, Report 895-15, Project RP-260, RCA 
Laboratories, Mar. 6, 1944. Div. 1 5-333.5 1-M2 

94. Trailing Wire Antenna — Power Limits, P. S. Carter, 

Report 895-16, Project RP-260, RCA Laboratories, 
Mar. 10, 1944. Div. 15-333.4-M2 

95. Antenna Coupling — Airborne Spot Jamming System of 
Project RP-358, P. S. Carter, Report 895-17, Research 
Project RP-260, RCA Laboratories, Apr. 11, 1944. 

Div. 15-333.1-M9 

96. Quado Indicator, W. A. Anderson, Report 895-18, 
Project RP-263, RCA Laboratories, Apr. 12, 1944. 

Div. 15-314.21-M2 

97. Instructions for Use of Narrow Band FM Adapter for 
Receiver BC-603-D, Warren H. Bliss, Report 895-19, 
Project RP-131, RCA Laboratories, Apr. 26, 1944. 

Div. 15-212. 11-M4 

98. AJ Characteristics of Beechnut, Eugene R. Shenk, James 
A. Spencer, and Elmer B. Anderson, Report 895-20, 
Project RP-229, RCA Laboratories, Apr. 15, 1944. 

Div. 15-212.11-M3 

99. Measurements on a 1200-ft Long Wave Antenna over 
Rocky Point Soil, N. E. Lindenblad, Report 895-21, 
Project RP-260, RCA Laboratories, May 2, 1944. 

Div. 15-333.52-Ml 

100. Identification of Ptdse Communication Systems, John B. 
Atwood and Grant E. Hansell, Report 895-22, Project 
RP-325, RCA Laboratories, May 15, 1944. 

Div. 15-211. 1-M9 

101. Measurements on 1200-ft Long Wave Antennas over Toby- 
hanna, Pennsylvania Soil, W. A. Miller, Report 895-23, 
Project RP-260, RCA Laboratories, June 20, 1944. 

Div. 15-333.52-M2 

102. Broad-Band Inverted-L Antenna, R. S. Wehner, Report 

895-24, Project RP-260, RCA Laboratories, July 20, 
1944. Div. 15-333.51-M3 

103. Pulse Amplitude Selective AGC Circuit, John B. Atwood 
and Grant E. Hansell, Report 895-25, Project RP-123, 
RCA Laboratories, July 22, 1944. Div. 15-383-M4 

104. PM vs FM Pulse Jamming of a Pulse Phase Modulation 

Communication System, John B. Atwood and Grant E. 
Hansell, Report 895-26, Project RP-123, RCA Labora- 
tories, Aug. 7, 1944. Div. 15-21 1.323-M3 

105. Measurements on 1200 ft, 2250 ft, and 3600 ft Long Wave 

Antennas over Sandy New Jersey Plains Soil, R. E. 
Franklin, Report 895-27, Project RP-260, RCA Labora- 
tories, Aug. 28, 1944. Div. 15-333.52-M3 

106. Demodulation Effect, J. Ernest Smith, Eugene R. Shenk, 
and James R. Weiner, Report 895-28, Project RP-229, 
RCA Laboratories, Sept. 18, 1944. 

Div. 15-384.2-Ml 

107. Antenna for Horizontal Polarization at UHF, R. S. 

Wehner, Report 895-29, Project RP-352, RCA Labora- 
tories, Oct. 19, 1944. Div. 15-333.3-M2 


108. The Importance of Removing Pulse Width Variations in a 
PFM Communication System, John B. Atwood and 
Grant E. Hansell, Report 895-30, Project RP-123, RCA 
Laboratories, Oct. 25, 1944. 

Div. 15-212. 13-M2 

109. Circular Loop Antennas at High Frequencies, P. S. 

Carter, Report 895-31, Project RP-260, RCA Labora- 
tories, Jan. 10, 1945. Div. 15-333. 21-M8 

110. A Flush Surface Antenna of the Slot- Cavity Type Having 

Wide Band Characteristics, N. E. Lindenblad, Report 
895-32, Project RP-260, RCA Laboratories, Mar. 26, 
1945. Div. 15-333.53-Ml 

111. Design Charts for Synthesis of Two-Element Broad-Band 
Matching Sections, R. S. Wehner, Report 895-33, Project 
RP-260, RCA Laboratories, Jan. 2, 1945. 

Div. 15-333. 51-M4 

112. Stopwatch, W. A. Anderson, Report 895-34, Project 
RP-263, RCA Laboratories, Jan. 18, 1945. 

Div. 15-402.3-Ml 

113. A Zero-Drag Aircraft Antenna for UHF, R. S. Wehner, 

Report 895-35, Project RP-260, RCA Laboratories, 
Jan. 15, 1945. Div. 15-332. 17-M2 

114. Pulse Communications J and AJ, PM, and PFM Sys- 

tems, John B. Atwood and Grant E. Hansell, Report 
895-36, Project RP-123, RCA Laboratories, Jan. 23, 
1945. Div. 15-211. 323-M4 

115. Quado Dual Indicator, W. A. Anderson, Report 895-37, 
Project RP-263, RCA Laboratories, Jan. 27, 1945. 

Div. 15-314.21-M3 

116. J Characteristics of AN /TRC-5 (XC-2) Radio Set, 
Bertram A. Trevor, Report 895-38, Projects RP-460 and 
SC-93.02, RCA Laboratories, May 29, 1945. 

Div. 15-211. 211-M9 

117. Vofiag Impulse Signaling System, J. Ernest Smith, 

James A. Spencer, E. R. Shenk, and L. F. Reinhold, 
Report 895-39, Projects RP-229 and SC-93.03, RCA 
Laboratories, Oct. 24, 1945. Div. 15-212.1 1-M9 

118. The Blanket System, H. O. Peterson, Warren H. Bliss, 
G. S. Wickizer, and G. L. Usselman, Report 895-40, 
Project RP-252, RCA Laboratories, Oct. 3, 1945. 

Div. 15-250-M2 

119. Final Report — OEMsr-895, H. H. Beverage, Report 
895-41, RCA Laboratories, Oct. 10, 1945. 

Div. 15-160-Ml 

120. Cathode Ray — Phototube Demodulation of Time Division 

Multiplex Pulse Signal, Bertram A. Trevor, Report 
895-42, Project RP-460 and SC-93.02, RCA Labora- 
tories, Oct. 17, 1945. Div. 15-344-M2 

121. Type P523-A Test Oscillator, David B. Sinclair and R. A. 
Soderman, Report 923-1, Project RP-270, General 
Radio Company, Dec. 7, 1943. 

Div. 15-511 -M3 

122. Crystal Rectifiers as Peak Voltmeters, A. P. G. Peterson, 

Report 923-2, Project RP-270, General Radio Com- 
pany, Jan. 7, 1944. Div. 15-384-Ml 

123. Type P525-A Signal Generator, A. P. G. Peterson, 

Report 923-3, Project RP-160, General Radio Company, 
June 5, 1944. Div. 15-512-M7 

124. Special Report on Window Tests, H. C. Pollock and F. L. 

Whipple, Report 931-1, General Electric Company, 

July 6, 1943. Div. 15-241-M3 


BIBLIOGRAPHY 


471 


125. Peter Tests on Chesapeake Bay, Siegfried Hansen and 
H. H. Race, Report 931-2, Project RP-156, General 
Electric Company, Aug. 24, 1943. 

Div. 15-403.1-Ml 

126. Peter Test at Radio Research Laboratory, Siegfried 
Hansen and H. H. Race, Report 931-3, Project RP-156, 
General Electric Company, Sept. 22, 1943. 

Div. 15-403. 1-M2 

127. Project Angels: An Investigation of Folding Corner Re- 
flectors, W. K. Kearsley, Report 931-4, Project RP-258, 
General Electric Company, Sept. 7, 1943. 

Div. 15-241. 3-Ml 

128. Constriction Oscillator, Lewis R. Roller, Report 931-5, 
Project RP-243, General Electric Company, Nov. 20, 

1943. Div. 15-343.21-M3 

129. The ZP-579, a 150 Watt Magnetron for the 350-750 
Megacycle Range, J. P. Blewett, Report 931-6, Project 
R P-244, General Electric Company, Feb. 14, 1944. 

Div. 15-341. 2-Ml 

130. The ZP-595 Magnetron, R. B. Nelson, R. V. Langmuir, 
and John P. Blewett, Report 931-7, Project RP-116, 
General Electric Company, Feb. 9, 1944. 

Div. 15-341.5-Ml 

131. Broad-Band Amplification With Grounded Grid Circuits, 
Siegfried Hansen, Report 931-8, Project RP-156, Gen- 
eral Electric Company, Feb. 10, 1944. 

Div. 15-383-M2 

132. Spectrum Analyzer, J. H. Rubel, T. Hudspeth, and R. 
E. Troell, Report 931-9, Project RP-347, General 
Electric Company, Mar. 18, 1944. 

Div. 15-513-M3 

133. Project Peter, H. H. Race and Siegfried Hansen, Report 

931-10, Project RP-156, General Electric Company, 
July 14, 1944. Div. 15-403. 1-M5 

134. Operating Instructions for Type RP-347 Spectrum Ana- 
lyzer, E. S. Miller and J. H. Rubel, Report 931-11, 
Project RP-347, General Electric Company, Aug. 23, 

1944. Div. 15-513-M6 

135. Amplification Characteristics of the L14 with Small Signal 
Input at 3000 Me, N. T. Lavoo, Report 931-12, Project 
RP-396, General Electric Company, Aug. 25, 1944. 

Div. 15-346-M3 

136. A Gold-Copper Alloy Solder, R. B. Nelson, Report 

931-13, Project RP-116, General Electric Company, 

May 30, 1944. Div. 15-346-M2 

137. A New Noise- Source Design, P. H. Peters, Jr., Report 

931-14, Project RP-393, General Electric Company, 

Dec. 20, 1944. Div. 15-343.241-M9 

138. Spectrum Analyzer RP-392, J. Kahnke, E. Taft, R. L. 
Watters, and L. Apker, Report 931-15, Project RP-392, 
General Electric Company, Feb. 1, 1945. 

Div. 15-513-M9 

139. Note on Reciprocity Failure in Crystal Mixers, L. Apker, 

Report 931-16, Project RP-392, General Electric Com- 
pany, Mar. 9, 1945. Div. 15-384.2-M2 

1 40. T heory of a Double Mixer for Spectrum A nalyzer A pplica- 
tions, L. Apker, E. Taft, and J. Dickey, Report 931-17, 
Projects RP-392, SC-99.06, and AC-299.06, General 
Electric Company, Apr. 2, 1945. Div. 15-513-MlO 

141. Reflection of Radar Waves with Special Application to 
Homing Missiles, H. Poritsky, Report 931-18, Projects 


RP-188 and SC-49, General Electric Company, Aug. 21, 

1945. , Div. 15-830-Ml 

142. A Wide-Band Spectrum Analyzer, E. Taft, J. Kahnke, 
R. L. Watters, and L. Apker, Report 931-19, Projects 
RP-392, SC-99y06, and AC-299.06, General Electric 
Company, Aug. 3, 1945. 

Div. 15-513-Mll 

143. Reciprocity Failure in Welded Germanium Crystals, J. 

Dickey and L. Apker, Report 931-20, Projects RP-392, 
SC-99.06, and AC-299.06, General Electric Company, 
Sept. 28, 1945. Div. 15-384. 11-Ml 

144. A Magnetron Filament Regulator, P. H. Peters, Jr., 
Report 931-21, Projects RP-244 and NS-218, General 
Electric Company, Nov. 16, 1945. 

Div. 15-341.6-M8 

145. Decay in Efficiency in the 5J29 Magnetron, T. R. Holer, 
Report 931-22, Projects SC-94.12, NS-208, and RP-244, 
General Electric Company, Oct. 22, 1945. 

Div. 15-341. 2-M3 

146. 100-1000 Watt CW Magnetron for the 90-1500 Me Range, 
D. A. Wilbur, R. V. Langmuir, and R. D. Gordon, 
Report 931-23, Service Projects RP-244 and NS-208, 
General Electric Company, Nov. 23, 1945. 

Div. 15-341.4-M15 

147. The ZP-633, a 25 Watt Magnetron for the 300-1500 Me 

Range, R. D. Gordon, Report 931-24, Projects RP-430a, 
SC-94.23, and AC-294.23, General Electric Company, 
Nov. 21, 1945. Div. 15-341. 1-M4 

148. Project Peter, Siegfried Hansen, Report 931-25, Projects 

RP-156 and NS-251, General Electric Company, Nov. 
16, 1945. Div. 15-403. 1-M6 

149. An I- F Amplifier with a Variable Input Impedance, R. L. 
Watters, Report 931-26, Projects RP-392, SC-99.06, and 
AC-299.06, General Electric Company, Nov. 8, 1945. 

Div. 15-314. 1-Ml 

150. Corner Reflectors {Angels), W. K. Kearsley, Report 
931-27, Projects RP-258, SC-96.02, and NA-180, Gen- 
eral Electric Company, Sept. 26, 1945. 

Div. 15-241. 3-M6 

151. The L-200, a 5 kw Triodefor the 70-350 Me Range, A. M. 
Gurewitsch, J. S. Hickey, and others. Report 931-28, 
Projects RP-394 and NA-102, General Electric Com- 
pany, Nov. 8, 1945. 

Div. 15-346-M4 

152. Tracing of Electron Trajectories Using the Differential 
Analyzer, John P. Blewett, Gabriel Kron, and others. 
Report 931-29, Projects RP-244 and RP-430a, General 
Electric Company, Nov. 23, 1945. 

Div. 15-346-M5 

153. The ZP-636 — Externally Tuned High Power Magnetron, 
R. B. Nelson, Report 931-30, Projects RP-116, and 
NS-278, General Electric Company, Nov. 21, 1945. 

Div. 15-341.4-M14 

154. Preproduction Experience with 100-1000 Watt CW Mag- 
netrons for the 90-1500 Me Range, M. C. Schramm, 
Report 931-31, Projects RP-158f and RP-244, General 
Electric Company, Oct. 18, 1945. 

Div. 15-341.4-M7 

155. Contract OEMsr-931, Final Report, John P. Blewett, 

Report 931-32, General Electric Company, Nov. 20, 
1945. Div. 15-150-Ml 


472 


BIBLIOGRAPHY 


156. The ZP-595—10 kw Magnetron Oscillator at 500 Me, 
R. V. Langmuir and R. B. Nelson, Report 931-33, 
Projects RP-116, SC-94.24, and NS-394.03, General 
Electric Company, Nov. 19, 1945. 

Div. 15-341. 5-M4 

157. Spectrum Analyzer RP-392K, E. Taft, J. Kahnke, and 

others. Report 931-34, Project RP-392, General Electric 
Company, Nov. 8, 1945. Div. 15-513-M9 

158. The ZP-652, 10-CM Tunable Magnetron, R. B. Nelson, 
Report 931-35, Projects RP-430a and SC-94.23, General 
Electric Company, Nov. 23, 1945. 

Div. 15-341.1-M5 

159. Jamming and Anti- Jamming of Telegraphy, E. Labin, 

D. D. Grieg, and R. B. Reade, Report 936-1, Federal 
Telephone and Radio Corporation Laboratories, Sept. 
10, 1943. Div. 15-210-Ml 

160. Jamming and Anti-Jamming of Telegraphy, E. Labin, 

D. D. Grieg, and R. B. Reade, Report 936-2, Federal 

Telephone and Radio Corporation Laboratories, Apr. 1, 
1944. Div. 15-210-Ml 

161. Jamming of Telegraphy Keyed Noise Jamming Signals, 

E. Labin, D. D. Grieg, and R. B. Reade, Report 936-3, 
Projects RP-159 and NLS-613, Federal Telephone and 
Radio Corporation Laboratories, July 25, 1944. 

Div. 15-211.321-M5 

162. Flight Test of Navy Type X-DBA Radio Direction Finder 
on B-24J Aircraft, H. H. Buttner, Report 936-4, Federal 
Telephone and Radio Laboratories, Jan. 18, 1945. 

Div. 15-313.11-Ml 

163. Final Summary Report, H. H. Buttner, Report 936-5, 
Projects RP-959, SC-93.05, and [N]-97.04, Federal Tele- 
phone and Radio Laboratories, Apr. 30, 1945. 

Div. 15-190-Ml 

164. Radio Communication System Protected Against Inter- 

ference, Report 937-1, Federal Telephone and Radio 
Laboratories, July 28, 1943. Div. 15-212.12-Ml 

165. Protected Communication System, E. M. Deloraine, 
Report 937-2, Project RP-124, Federal Telephone and 
Radio Laboratories, Apr. 28, 1944. 

Div. 15-212.12-M4 

166. Radio Communication System Protected Against Inter- 
ference, H. Busignies, S. H. Dodington, and G. R. Clark, 
Report 937-3, Projects RP-124 and AC-293.04, Federal 
Telephone and Radio Laboratories, July 12, 1945. 

Div. 15-212. 12-M5 

167. 50-Watt Jamming Transmitter of the Simplified Double- 
Sideband Dina Type, R. C. Shaw, Report 940-1, Project 
RP-199, Bell Telephone Laboratories, June 24, 1943. 

Div. 15-321.1 1-Ml 

168. High-Power Barrage Jammer, L. G. Young, Report 

940-2, Project RP-155, Bell Telephone Laboratories, 
July 15, 1943. Div. 15-321. 1-Ml 

169. Barrage Jammer, L. G. Young and G. V. Dale, Report 

940-3, Project RP-153, Bell Telephone Laboratories, 
Aug. 17, 1943. Div. 15-321. 1-M2 

170. Efficiency of Spark Transmitters, Charles R. Burrows, 

Report 940-4, Project RP-199, Bell Telephone Labora- 
tories, Aug. 24, 1943. Div. 15-323-M2 

171. Pi-Type Admittance Transforming Networks, Charles R. 

Burrows, Report 940-5, Bell Telephone Laboratories, 
June 18, 1943. Div. 15-383-Ml 


172. Spark Jammer Experiments at Deal, L. E. Hunt, Report 

940-6, Project RP-199, Bell Telephone Laboratories, 
Sept. 29, 1943. Div. 15-21 1.3-Ml 

173. Preliminary Specification of 920-1 1-E Jamming Trans- 
mitter, J. C. Schelleng, Report 940-7, Project RP-199, 
Bell Telephone Laboratories, Oct. 1, 1943. 

Div. 15-321. 12-Ml 

174. Radio- Frequency Requirements of Barrage Jamming, 
VV. J. Albersheim, Report 940-8, Project RP-235, Bell 
Telephone Laboratories, Oct. 20, 1943. 

Div. 15-231-M4 

175. Noise Output of 884 Gas T riode at High Frequencies, A. E. 
Kerwien, Report 940-9, Project RP-199, Bell Telephone 
Laboratories, Nov. 3, 1943. 

Div. 15-343.242-M2 

176. A Novel Method of Frequency Modulation and a lO-Watt 
Expendable Jammer, L. G. Young, Report 940-10, 
Project RP-132, Bell Telephone Laboratories, Dec. 9, 

1943. Div. 15-412-M5 

177. Use of the Self-Quenched Oscillator in the “Pad” Barrage 
Jamming Transmitter, A. E. Kerwien, Report 940-11, 
Project RP-199, Bell Telephone Laboratories, Jan. 3, 

1944. Div. 15-321. 12-M2 

178. Development of a Lightweight Dina Transmitter, R. J. 
Kircher and R. VV. Friis, Report 940-12, Project RP-199, 
Bell Telephone Laboratories, Jan. 28, 1944. 

Div. 15-321. 11-M3 

179. Mechanical Design of Chicks, Parts I II, R. C. Shaw 
and R. VV. Friis, Report 940-13, Project RP-132, Bell 
Telephone Laboratories, Mar. 20, 1944. 

Div. 15-412-Ml 

180. Expendable Jammer Deal Vacuum Tube 1 to 7 Me Dina 

Chick, J. P. Schafer, L. E. Hunt, G. VV Dale, and L. G. 
Young, Report 940-14, Project RP-132, Bell Telephone 
Laboratories, Apr. 1, 1944. Div. 15-412-M7 

181. Improved Jamming A ction of Multiple Pad, {AN / ART-2) 

Transmitters, VV. J. Albersheim and F. F. Merriam, 
Report 940-16, Project RP-199, Bell Telephone Labora- 
tories, Oct. 2, 1944. Div. 15-321. 12-M4 

182. Suppression of Harmonics in 15 KW Cigar Output, J. P. 
Schafer and L. E. Hunt, Report 940-17, Project RP-356, 
Bell Telephone Laboratories, Oct. 16, 1944. 

Div. 15-402. 2-M5 

183. Audio Frequency Modulation for 15 KW Cigar, J. P. 

Schafer, Report 940-18, Project RP-356, Bell Telephone 
Laboratories, Oct. 16, 1944. Div. 15-402. 2-M6 

184. Noise Modulation of 15 KW Ground Cigar, J. P. Schafer, 
L. E. Hunt, and G. V. Dale, Report 940-19, Project 
RP-356, Bell Telephone Laboratories, Oct. 17, 1944. 

Div. 15-402. 2-M7 

185. Development of AM-66 /AR-XR Radio Amplifier, L. G. 
Young, N. F. Schlaack, and others. Report 940-20, 
Project RP-272, Bell Telephone Laboratories, Feb. 3, 

1945. Div. 15-322.21-M4 

186. Barrage Communications Jamming Studies and Develop- 
ment, M. J. Kelly, Report 940-21, Projects RP-132 and 
RP-150, Bell Telephone Laboratories, Feb. 20, 1945. 

Div. 15-231-M6 

187. Jamming Generalized Plane to Ground Propagation 

Curves, A. C. Peterson, Report 966-1, Bell Telephone 
Laboratories, Mar. 16, 1943. Div. 15-21 1.1-M4 


BIBLIOGRAPHY 


473 


188. Investigation of Jamming of Radio Telegraph Communi- 
cation, R. B. Shanck and V. A. Douglas, Report 966-2, 
Bell Telephone Laboratories, Mar. 29, 1943. 

Div. 15-211. 1-M5 

189. Conversion of GO-9 for RCM Purposes, H. H. Benning, 

Report 966-3, Bell Telephone Laboratories, Mar. 24, 
1943. Div. 15-321.3-M2 

190. Audio Frequency Noise Generators, H. H. Benning, 

Report 966-4, Bell Telephone Laboratories, May 26, 
1943. Div. 15-343.21-M2 

191. The A verage Characteristics Impedance Kq of Fan Dipoles, 

W. C. Babcock, Report 966-5, Bell Telephone Labora- 
tories, May 24, 1943. Div. 15-333. 1-M3 

192. Jamming Solution of Transmission Problems, A. C, 

Peterson, Report 966-6, Project C-63, Bell Telephone 
Laboratories, May 22, 1943. Div. 15-21 1.1-M2 

193. Propagation Curves, Report 966-6C, Bell Telephone 

Laboratories, October 1944, Div. 15-810-M2 

194. Tests on Experimental Spark Jammer, Chick I, V. A. 

Douglas, Report 966-7, Bell Telephone Laboratories, 
July 9, 1943. Div. 15-412-M2 

195. The Average Characteristic Impedance of Multiwire 
Cylindrical Cage Dipoles, W. C. Babcock, Report 966-8, 
Bell Telephone Laboratories, July 1, 1943. 

Div. 15-333.1-M5 

196. Tests on AN j ARQ-2, Jackal, V. A. Douglas, Report 
966-9, Bell Telephone Laboratories, Aug. 10, 1943. 

Div. 15-401. 2-Ml 

197. Modification of the SCR-808 for Jamming Purposes, V. A. 
Douglas and W. E. Evans, Report 966-10, Project 
RP-148, Bell Telephone Laboratories, Nov. 23, 1943, 

Div. 15-321. 3-M4 

198. Jamming of AM and FM Communications, H. H. 

Benning, Report 966-11, Bell Telephone Laboratories, 
July 28, 1943. Div. 15-211. 1-M6 

199. Jamming — Optimum Size of Chicks, A. C, Peterson, 

Report 966-12, Bell Telephone Laboratories, Aug. 2, 
1943. Div. 15-412-M3 

200. Results of VHF Jamming at Orlando, C, L. Cahill, 

Report 966-13, Bell Telephone Laboratories, Sept. 22, 
1943. Div. 15-722-Ml 

201. Comparison of Measured and Theoretical Impedance 

Characteristics of Cylindrical Radiators, S. A. Schel- 
kunoff. Report 966-14, Bell Telephone Laboratories, 
June 28, 1943. Div. 15-333. 1-M4 

202. The Input Impedance of Hollow Cylindrical Dipoles, 

W, C. Babcock, Report 966-15, Bell Telephone Labora- 
tories, Aug. 25, 1943. Div. 1 5-333. 1-M6 

203. Conversion of GO-9 for RCM Purposes, H. H. Benning 

and W. E. Evans, Report 966-16, Bell Telephone 
Laboratories, Sept. 21, 1943. Div, 15-321. 3-M3 

204. Report of RCM Activities in Tennessee Maneuvers, R. L. 

Robbins, Report 966-17, Bell Telephone Laboratories, 
Sept. 24, 1943. Div. 15-72 1-Ml 

205. Jamming Signals for Telegraph Communications, H. H. 

Benning, Report 966-18, Bell Telephone Laboratories, 
Sept. 22, 1943. Div. 15-211.321-M3 

206. Jamming of German G.C.I. Ground-to- Plane Communica- 

tion by Equipment Carried by Bombers, W. C. Babcock, 
Report 966-19, Bell Telephone Laboratories, Oct. 22, 
1943. Div. 15-711-Ml 


207. Supplementary Tests of Effectiveness of Jackal {AN/ 
ARQ-2) Equipment, V. A. Douglas, Report 966-20, Bell 
Telephone Laboratories, 06t. 22, 1943. 

Div. 15-401.2-M2 

208. Investigation of the See Saw Signals, K. G. Jansky, 

Report 966-21, Project RP-109, Bell Telephone Labora- 
tories, Nov. 10, 1943. Div. 15-840-Ml 

209. Jamming Analysis of Chick Problem, G, J. Heinzelman, 

Report 966-22, Project RP-132, Bell Telephone Labora- 
tories, Feb. 5, 1944. Div. 15-412-M6 

210. Activities of a Provisional Radio Signal Intelligence 

Battalion in the Tennessee Maneuvers, R. L. Robbins, 
Report 966-23, Project RP-326, Bell Telephone Labora- 
tories, Dec. 28, 1943. Div. 15-721-M2 

211. Anti- Jamming Effectiveness of Vacuum Tube Limiter, 
H. H. Benning, Report 966-24, Project RP-109, Bell 
Telephone Laboratories, Dec. 28, 1943. 

Div. 15-212. 12-M2 

212. Mechanical FM Jammers Effectiveness Against AM 

Voice Links, V. A. Douglas, E. O. Bernard, and M. 1. 
Risley, Report 966-25, Project RP-109, Bell Telephone 
Laboratories, Apr. 7, 1944. Div. 15-402. 2-Ml 

213. Investigation of Multi-Carrier Homodyne Signal for CW 

Telegraph Jamming, C. R. Englund, Report 966-26, 
Project RP-109, Bell Telephone Laboratories, May 22, 
1944. Div. 15-211.321-M4 

214. Airborne Spot Jamming System Study, W. C. Babcock, 
R. L. Robbins, and others. Report 966-27, Project 
RP-358, Bell Telephone Laboratories, Apr. 27, 1944. 

Div. 15-232-M2 

215. Performance of Chick Jammers, G. J. Heinzelman and 
J. W. Emling, Report 966-28, Project RP-132, Bell 
Telephone Laboratories, June 15, 1944. 

Div. 15-412-M8 

216. Conversion of Intermediate Frequency Unit of GO-9 

Transmitter for Telegraph RCM Purposes, V. L. Dzwon- 
czyk. Report 966-29, Project RP-148, Bell Telephone 
Laboratories, May 23, 1944. Div. 15-321. 3-M5 

217. Effectiveness Tests of Pad {AN/ ART-2) Used against 
AM Nets, V. A. Douglas, Report 966-30, Project 
RP-109, Bell Telephone Laboratories, May 9, 1944. 

Div. 15-321. 12-M3 

218. Jamming and A nti- Jamming of Radio Communications — 

Introductory Survey of Technical Considerations, Report 
966-31, Project RP-109, Bell Telephone Laboratories, 
May 16, 1944. Div. 15-210-M2 

219. Susceptibility of American FM Communication Equip- 
ment to Jamming by Mechanical FM Barrage Jammers — ■ 
Test of SCR-608, SCR-609 and SCR-808, V. A. Douglas, 
Report 966-32, Project RP-109, Bell Telephone Labora- 
tories, Sept. 1, 1944. 

Div. 15-211. 212-M3 

220. Tests to Compare Ability of NDRC and Military Opera- 
tors in Reception of Telegraph Signals Through Interfer- 
ence, R. B. Shanck, Report 966-33, Project RP-109, Bell 
Telephone Laboratories, Oct. 18, 1944. 

Div. 15-650-M2 

221. Field Trial of Modified SCR-828 Radio Equipment at 

Florosa Field, Florida, M. C. Francis and H. C. Pollock, 
Report 966-34, Project RP-109, Bell Telephone Labora- 
tories, May 20, 1944. Div. 15-722-M3 


474 


BIBLIOGRAPHY 


222. Mechanical FM Jammers Effect of Jittering, W. A. 

Getchell, G. J. Heinzelman, and J. L. Lindner, Report 
966-35, Project RP-109, Bell Telephone Laboratories, 
Sept. 1, 1944. Div. 14-21 1.31-M4 

223. Study of Airborne Barrage Jamming Systems at Fre- 
quencies of 27 to 42 Me, W. J. Albersheim, V. A. Douglas, 
J. W. Emling, and W. H. Tidd, Report 966-36, Project 
RP-150, Bell Telephone Laboratories, Nov. 10, 1944. 

Div. 15-231-M5 

224. Effectiveness Tests on AN / ART-3 {Jackal) Jammer 
Against SCR-608, SCR-609 and German UkwEe Equip- 
ments, G. J. Heinzelman, Report 966-37, Project RP- 
109, Bell Telephone Laboratories, Oct. 12, 1944. 

Div. 15-401.2-M6 

225. The Stingeree Antenna, W. C. Babcock, E. O. Bernard, 
and others. Report 966-38, Project RP-410, Bell Tele- 
phone Laboratories, Dec. 9, 1944. 

Div. 15-332.17-Ml 

226. Comparison of Several Types of Microphones in Effective- 
ness Tests Using FuGe 16 as the Victim Link, J. J. 
Lindner and G. J. Heinzelman, Report 966-39, Project 
RP-109, Bell Telephone Laboratories, Oct. 3, 1944. 

Div. 15-401. 2-M5 

227. Communication RCM in Pacific A rea General Considera- 

tions, H. H. Benning, Report 966-40, Bell Telephone 
Laboratories, Sept. 29, 1944. Div. 15-712-M2 

228. Jamming Susceptibility of the Japanese Model 99 Type 

Hi 3 Radio Set, G. J. Heinzelman and J. L. Lindner, 
Report 966-41, Project RP-109, Bell Telephone Labora- 
tories, Nov. 13, 1944. Div. 15-211.23-Ml 

229. Jamming Susceptibility of the Japanese Meteorological 

Receiving Set No. 775, G. J. Heinzelman and J. L. 
Lindner, Report 966-42, Project RP-109, Bell Telephone 
Laboratories, Dec. 9, 1944. Div. 15-211.23-M2 

230. A Phonograph Record: What Does Jamming Sound Like? 

R. L. Robbins, Report 966-43, Bell Telephone Labora- 
tories, Dec. 7, 1944. Div. 15-630-Ml 

231. Simple Noise Generators for Static Burst Jamming, R. L^ 
Robbins, Report 966-44, Project RP-148, Bell Tele- 
phone Laboratories, Dec. 21, 1944. 

Div. 15-211. 321-M6 

232. Jamming Susceptibility of the Japanese 99 Mark 4 VHF 
Radio Set, G. J. Heinzelman, Report 966-45, Project 
RP-966, Bell Telephone Laboratories, Jan. 20, 1945. 

Div. 15-21 1.23-M3 

233. Jamming Susceptibility of the Japanese 94 Mark 5 
Receiver, G. J. Heinzelman, Report 966-46, Project 
RP-109, Bell Telephone Laboratories, Feb. 7, 1945. 

Div. 15-21 1.23-M4 

234. Stingeree Antenna Pattern, M. E. Campbell, C. R. Eck- 
berg, and M. C. Francis, Report 966-47, Project RP-410, 
Bell Telephone Laboratories, Mar. 15, 1945. 

Div. 15-332. 17-M3 

235. Comparison of AM-33 and AM-66 Amplifiers, M. E. 

Campbell, C. R. Eckberg, and M. C. Francis, Report 
966-48, Project RP-272B, Bell Telephone Laboratories, 

Mar. 15, 1945. Div. 15-322.21-M5 

236. Jamming Susceptibility of the Japanese Radio Set TM- 

305-Cl, G. J. Heinzelman and E. O. Bernard, Report 
966-49, Project RP-109, Bell Telephone Laboratories, 

Feb. 8, 1945. Div. 15-21 1.23-M5 


237. A Technique for Conducting Field Jamming Tests, M. C. 
Francis, Report 966-50, Projects SC-95.08 and RP-272b, 
Bell Telephone Laboratories, Apr. 20, 1945. 

Div. 15-211. 2-Ml 

238. Description of Communication Ferret C-1, H. H. Benning 

and G. J. Heinzelman, Report 966-51, Projects RP-440 
and SC-98.05, Bell Telephone Laboratories, June 8, 
1945. Div. 15-311. 113-Ml 

239. Modifications and Performance of R-44/ A RR- 5 Receivers 
for Use in Communications Ferrets, E. O. Bernard and 
C. R. Eckberg, Report 966-52, Projects RP-440B and 
AC-291.01, Bell Telephone Laboratories, Aug. 23, 1945. 

Div. 15-31 1.1 12-M2 

240. Modifications and Performance of R-45/ARR-7 Receivers 
for Use in Communications Ferrets, R. V. Crawford, 
Report 966-53, Projects RP-440B and AC-291.01, Bell 
Telephone Laboratories, Aug. 22, 1945. 

Div. 15-311. 112-Ml 

241. Countermeasures against Japanese High Frequency Di- 

rection Finding, K. L. Maurer, Report 966-54, Projects 
RP-422 and SC-95.16, Bell Telephone Laboratories, 
July 7, 1945. Div. 15-211. 23-M7 

242. Countermeasures and A 7iti- Countermeasures for Radio 

Navigation Aids — Survey of Basic Technical Considera- 
tions, K. L. Maurer, Report 966-55, Projects RP-422 
and SC-95.16, Bell Telephone Laboratories, Oct. 15, 
1945. Div. 15-250-M3 

243. Final Report on Study of Radio Jamming and Anti- 
jamming, M. L. Almquist and R. P. Booth, Report 
966-56, Bell Telephone Laboratories, Oct. 31, 1945. 

Div. 15-180-Ml 

244. Automatic Tmiing in Jamming Equipment, H. M. 

Straube, Report 993-1, Project RP-122, Bell Telephone 
Laboratories, Aug. 13, 1943. Div. 15-41 1-M2 

245. Preliminary Design of Airborne Multiple Spot Jamming 
System, E. R. Taylor, Report 993-2, Project RP-122, 
Bell Telephone Laboratories, Aug. 23, 1944. 

Div. 15-232-M3 

246. Listening Through and Jammer Alignment Systems, E. R. 
Taylor, Report 993-3, Projects RP-122, SC-95.11, and 
NS-128, Bell Telephone Laboratories, June 8, 1945. 

Div. 15-232-M6 

247. Some Considerations Governing DesigJi of Electromagnets 
for Piccolo Series of Multi- Anode Magnetrons, Lewi 
Tonks, Report 1019-1, Projects RP-158A and NS- 
394.02, General Electric Company, June 6, 1945. 

Div. 15-341.4-M2 

248. Development of the ZP-616 Magnetroii, H. C. Hertha, 

R. B. Nelson, and T. C. Swartz, Report 1019-2, Projects 
SC-94.25, NS-394.02, and RP-158A, General Electric 
Company, Sept. 27, 1945. Div. 15-341. 4-M4 

249. Vacuum Thermocouples Used m Standing Wave De- 

tectors, H. C. Hertha, Report 1019-3, Service Projects 
RP-158a, SC-94.25, and NS-394.02, General Electric 
Company, Oct. 1, 1945. Div. 15-525-M2 

250. Parasitic Resonance Studies on the ZP-597 Magnetron, 

A. H. Sharbaugh, Report 1019-4, Projects SC-94.25, 
NS-394.02, and RP-158A, General Electric Company, 
Sept. 18, 1945. Div. 15-341.4-M3 

251. General Report on Piccolo Project — 1-kw Tunable CW 
Magnetrons, Lewi Tonks, J. S. Burgess, and others. 


BIBLIOGRAPHY 


475 


Report 1019-5, Projects RP-158A, SC-94.25, and NS- 
394.02, General Electric Company, Oct. 29, 1945. 

Div. 15-341.4-MlO 

252. L-104, X-Band Piccolo, R. A. Dehn, W. H. Teare, and 

S, E. Webber, Report 1019-6, Projects RP-158a, NA- 
156, and NS-394.02, General Electric Company, Oct. 25, 
1945. Div. 15-341.4-M8 

253. Development of ZP-594 Multi-Vane Magnetron, R. I. 
Reed, Report 1019-7, Projects RP-158A, SC-94.25, and 
NS-394.02, General Electric Company, Oct. 29, 1945. 

Div. 1 5-341. 4-M 11 

254. History of the Development of the ZP-597 Multi-Vane 
Magnetron, P. W. Crapuchettes, R. I. Reed, and R. J. 
Stupp, Report 1019-8, Projects RP-158A, SC-94.25, and 
NS-394.02, General Electric Company, Oct. 29, 1945. 

Div. 15-341.4-M12 

255. Vulnerability of the FuG 16 Receiver to Jamming of the 
Cigar Type, S. L. Bailey, Report 1024-1, Project RP- 
189, Jansky and Bailey, January 1944. 

Div. 15-21 1.22-M2 

256. Gas Tube Noise Generator Development, Ronald H. 
Culver and S. L. Bailey, Report 1024-2, Project RP-189, 
Jansky and Bailey, January 1944. Div. 15-343. 2 1-M4 

257. Study of Methods of Decreasing Susceptibility of FM 

Receivers to CW Jamming, Delmer C. Ports and S. L. 
Bailey, Report 1024-3, Project RP-189, Jansky and 
Bailey, March 1944. Div. 15-212. 11-M2 

258. Report on Tests Made on Signal Corps Receiver B C-603-D, 
Oscar W. B. Reed, Jr., and S. J. Bailey, Report 1024-4, 
Project RP-189, Jansky and Bailey, April 1944. 

Div. 15-211.211-Ml 

259. Investigation of the Vulnerability to Jamming of the 
SCR-609-A Radio Set, Frank T, Mitchell, Jr., Paul F. 
Hoffmann, and S. L. Bailey, Report 1024-5, Project 
RP-189, Jansky and Bailey, May 1944. 

Div. 15-211. 211-M2 

260. Preliminary Report of Pulse Tests on Receiver BC-624-A, 

Oscar W. B. Reed, Jr., Elmer H. Scheibe, and S. L. 
Bailey, Report 1024-6, Project RP-189, Jansky and 
Bailey, June 1944. Div. 15-212.11-M6 

261. Report of Tests Made on Radio Set AN/TRC-1 and 
Associated Equipment, Oscar W. B. Reed, Jr., Elmer 
H. Scheibe, and S. L. Bailey, Report 1024-7, Project 
RP-189, Jansky and Bailey, June 1944. 

Div. 15-211.212-Ml 

262. Definitions and Methods for Jamming Effectiveness Test- 

ing in Radiotelephone Countermeasures Work, W. J. 
Albersheim, M. L. Almquist, H. H. Benning, V. A. 
Douglas, J. W. Emling, S. L. Bailey, and J. H. Moore, 
Report 1024-8, Project RP-189, Jansky and Bailey, 
July 1944. Div. 15-211. 1-MlO 

263. Investigations of the Vulnerability to Jamming of the 

SCR-300-A Radio Set, Paul F. Hoffmann and S. L. 
Bailey, Report 1024-9, Project RP-189, Jansky and 
Bailey, August 1944. Div. 15-21 1.21 1-M3 

264. Investigation of the Vulnerability to Jamming of the 233 A 

Radio Set, Oscar W. B. Reed, Jr., Elmer H. Scheibe, and 
S. L. Bailey, Report 1024-10, Project RP-189, Jansky 
and Bailey, October 1944. Div. 15-21 1.214-M2 

265. Investigation of the Vulnerability to Jamming of the Radio 
Receiver BC-639-A, Oscar W. B. Reed, Jr., Elmer H. 


Scheibe, and S. L. Bailey, Report 1024-11, Project 
RP-189, Jansky and Bailey, September 1944. 

! Div. 15-211. 212-M2 

266. Final Report of the Vulnerability to Jamming of Radio 
Receiver BC-624-AM, Oscar W. B. Reed, Jr., Elmer H. 
Scheibe, and S. L. Bailey, Report 1024-12, Project 
RP-189, Jansky and Bailey, September 1944. 

Div. 15-211. 214-Ml 

267. Comparison of the Vulnerability to Jamming of Three 

Amplitude Modulation Aircraft Service Radio Receivers, 
Oscar W. B. Reed, Jr., Elmer H. Scheibe, and S. L. 
Bailey, Report 1024-13, Project RP-189, Jansky and 
Bailey, October 1944. Div. 15-21 1.214-M3 

268. Investigation of the Vulnerability to Jamming of the Radio 

Receiver BC-348-R, Paul F. Hoffmann and S. L. Bailey, 
Report 1024-14, Project RP-189, Jansky and Bailey, 
November 1944. Div. 15-21 1.214-M4 

269. Memorandum Concerning the Advantage of Clipping Peak 

Audio Voltages Prior to Modulating When Subjected to 
Certain Types of Interference, Delmer C. Ports and S. L. 
Bailey, Report 1024-15, Project RP-189, Jansky and 
Bailey, December 1944. Div. 15-212. 11-M7 

270. Investigation of the Vulnerability to Jamming of the 

BC-342-N Radio Receiver with Supplement Covering the 
BC-312-N Receiver, Elmer H. Scheibe and S. L. Bailey, 
Report 1024-16, Project RP-189, Jansky and Bailey, 
December 1944. Div. 15-211. 211-M4 

271. Memorandum on the Jamming Effectiveness of a Modified 

Step Tone Jammer, Frank T. Mitchell, Jr., and S. L. 
Bailey, Report 1024-17, Project RP-189, Jansky and 
Bailey, January 1945. Div. 15-211. 321-M7 

272. Investigation of the Vulnerability to Jamming of the Radio 

Receiver BC-652-A, Paul F. Hoffmann and S. L. Bailey, 
Report 1024-18, Project RP-189, Jansky and Bailey, 
January 1945. Div. 15-211. 211-M5 

273. Investigation of the Vulnerability to Jamming of the Radio 

Receiver BC-669-C, Oscar W. B. Reed, Jr., and S. L. 
Bailey, Report 1024-19, Project RP-189, Jansky and 
Bailey, January 1945. Div. 15-21 1.21 1-M6 

274. Investigation of the Vulnerability to Jamming of the Radio 

Receiver BC-654-A, Oscar W. B. Reed, Jr., and S. L. 
Bailey, Report 1024-20, Project RP-189, Jansky and 
Bailey, January 1945. Div. 15-21 1.21 1-M7 

275. Memorandum Concerning Jamming Vulnerability Tests 
on Six High Frequency Amplitude Modulated Receivers, 
Paul F. Hoffmann and S. L. Bailey, Report 1024-21, 
Project RP-189, Jansky and Bailey, February 1945. 

Div. 15-211.21-Ml 

276. Investigation of the Operating Characteristics of Radio Set 

SCR-536, Elmer H. Scheibe and S. L. Bailey, Report 
1024-22, Project RP-189, Jansky and Bailey, February 
1945. Div. 15-211. 211-M8 

277. Investigation of the Vulnerability to Jamming of the 
Original and Modified AN/ ARC-1 Radio Set, Elmer H. 
Scheibe and S. L. Bailey, Report 1024-23, Project RP- 
189, Jansky and Bailey, March 1945. 

Div. 15-211. 214-M5 

278. The AJ Characteristics of FM Receivers, Delmer C. 
Ports and S. L. Bailey, Report 1024-24, Project RP-189, 
Jansky and Bailey, March 1945. 


Div. 15-212.11-M8 


476 


BIBLIOGRAPHY 


279. Investigation of the Vulnerability to Jamming of Aircraft 
Receiver Model ARB, Paul F. Hoffmann and S. L, 
Bailey, Report 1024-25, Projects RP-189 and SC-93.01, 
Jansky and Bailey, May 1945. 

Div. 15-211.214-M6 

280. Investigation of the Electrical Characteristics and the 

Vulnerability to Jamming of the Radio Set SCR-511-B, 
Oscar W. B. Reed, Jr., and S. L. Bailey, Report 1024-26, 
Projects RP-189 and SC-93.01, Jansky and Bailey, June 
1945. Div. 15-211. 211-MlO 

281. Use of J'/S Ratio in RF Pulse Jamming Tests and 
Results of Vulnerability Studies of an ARB Receiver 
Using the Goodyear Limiter, Paul F. Hoffmann and S. L. 
Bailey, Report 1024-27, Projects RP-189 and SC-93.01, 
Jansky and Bailey, July 1945. 

Div. 15-211. 1-Mll 

282. Analysis of Electrical Circuits of the AN/ ARC-1 Radio 

Set, Elmer H. Scheibe and S. L. Bailey, Report 1024-28, 
Projects RP-189 and SC-93.01, Jansky and Bailey, 
August 1945. Div. 15-383-M7 

283. Investigation of the Electrical Characteristics and the 

Vulnerability to Jamming of the Radio Set AN/TRR-2, 
Oscar W. B. Reed, Jr., and S. L. Bailey, Report 1024-29, 
Projects RP-189 and SC-93.01, Jansky and Bailey, 
August 1945. Div. 15-211. 213-Ml 

284. Investigation of the Vulnerability to Jamming of the 

Model 96 Mark 4E Japanese Transmitter-Receiver, 
Elmer H. Scheibe and S. L. Bailey, Report 1024-30, 
Projects RP-109a and AC-295.10, Jartsky and Bailey, 
September 1945. Div. 15-211.23-M8 

285. Electrical Characteristics of Radio Set A N/ TRC-8 {X C-3) , 
Elmer H. Scheibe and S. L. Bailey, Report 1024-31, 
Project RP-189, Jansky and Bailey, September 1945. 

Div. 15-211. 211-Mll 

286. Vulnerability Study of Japanese Model B Radio Set, Paul 

F. Hoffmann and S. L. Bailey, Report 1024-32, Projects 
RP-109a and AC-295.10, Jansky and Bailey, September 
1945. Div. 15-211.23-M9 

287. Investigation of the Vulnerability to Jamming of the 
AN/SRW-2 {XA-1) Receiver, Stuart L. Bailey, Report 
1024-33, Projects RP-189, AC-293.01, SC-93.01, and 
NS-393.01, Jansky and Bailey, October 1945. 

Div. 15-211. 213-M2 

288. Final Report on Vulnerability of Radio Receivers to 
Jamming, Stuart L. Bailey and Delmer C. Ports, Report 
1024-34, Projects RP-189, AC-203.01, and NS-393.01, 
Jansky and Bailey, December 1945. 

Div. 15-211. 1-M12 

289. Development of a Sealed-off Resnatron, E. Labin, M. 

Arditi, J. Glauber, and M. Charchian, Report 1034-1, 
Project RP-247, Federal Telephone and Radio Corpora- 
tion, May 31, 1945. Div. 15-342-M4 

290. Mica Windows for Waveguide Output Magnetrons (Divi- 
sion 14 Report 366, Div. 14-233. 423-M9), L. Malter, 
R. L. Jepsen, and L. R. Bloom, Report 1043-1, Radio 
Corporation of America, Dec. 5, 1944. 

Div. 15-341.6-M2 

291. A Tantalum Cylinder Cathode for C.W. Magnetrons, 

R. L. Jepsen, Report 1043-2, Projects RP-430-c, SC- 
94.23, and NS-394.01, Radio Corporation of America, 
Jan. 15, 1945. Div. 15-344.M1 


292. Waveguide Output Magnetrons Employing Fused Quartz 
Output Transformers (Division 14 Report 367), L. 
Malter and J. L. Moll, Report 1043-3, Radio Corpora- 
tion of America, Jan. 15, 1945. 

Div. 15-341.6-M3 

293. Technical Report on K-Band Magnetron (Division 14 
Report 444, Div. 14-232. 111-M8), J. A. Beard, L. R. 
Bloom, W. H. Hayman, Han Chuan Hu, R. L. Jepsen, 
L. Malter, J. L. Moll, and I. M. Sieber, Report 1043-4, 
Radio Corporation of America, Mar. 1, 1945. 

Div. 15-341. 6-M4 

294. An Extension of Clogsten's Scaling Formulas to Include 
Change of Number of Slots, Han Chuan Hu, Report 
1043-5, Projects RP-430-c and SC-94.23, Radio Cor- 
poration of America, May 15, 1945. 

Div. 15-341.6-M5 

295. The A- 131 — A Tunable X-Band CW Magnetron, L. 

Malter, R. L. Jepsen, L. R. Bloom, Han Chuan Hu, and 
J. L. Moll, Report 1043-6, Projects RP-244-B, NA-156, 
and NS-394.01, Radio Corporation of America, Nov. 15, 
1945. Div. 15-341. 3-M2 

296. The A-132 — A Tunable CW Magnetron, R. B. Vande- 
grift. Report 1043-7, Projects SC-94.25 and RP-158-D, 
Radio Corporation of America, Nov. 15, 1945. 

Div. 15-341.4-M13 

297. The A- 133— A Tunable CW Magnetron, R. B. Vande- 
grift. Report 1043-7, Projects SC-94.25 and RP-158-D, 
Radio Corporation of America, Nov. 15, 1945. 

Div. 15-341.4-M13 

298. A Grid Controlled Photo- Multiplier and Its Application to 
Regeneratively Increasing Noise Output, Alan M. Glover, 
Ralph W. Engstrom, and W. J. Pietenpol, Report 
1060-1, Project RP-196, Radio Corporation of America, 
May 16, 1944. 

Div. 15-343.1-M5 

299. Final Report on the Investigation and Manufacture of 
Noise Sources at RCA, Alan M. Glover, Ralph W. 
Engstrom, and W. J. Pietenpol, Report 1060-2, Project 
RP-196, Radio Corporation of America, Mar. 7, 1945. 

Div. 15-343.1-M7 

300. High Power Communications Jammer, Robert M. Baker 

and Benedict Cassen, Report 1107-1, Project RP-197, 
Westinghouse Electric and Manufacturing Company, 
Apr. 10, 1944. Div. 15-402.2-M2 

301. High Power Communications Jammer, David Bartlett, 
Report 1107-2, Project RP-197, Westinghouse Electric 
and Manufacturing Company, June 11, 1944. 

Div. 15-402.2-M3 

302. Notes on Oscillators in Connection with Electronic Tuning 

for Panoramic Reception, Joseph I. Heller, Report 
1138-1, Project RP-307, Panoramic Radio Corporation, 
Mar. 8, 1944. Div. 15-353-Ml 

303. Notes on Factors Affecting the Selection of Values for Use 
in the Phase Net of Reactance Tubes, Joseph I. Heller and 
Oscar Friedman, Report 1138-2, Project RP-307, Pano- 
ramic Radio Corporation, Oct. 23, 1944. 

Div. 15-345-M4 

304. Final Report on Electronic Tuning for Panoramic Re- 
ception, Joseph I. Heller, Report 1138-3, Project RP-307, 
Panoramic Radio Corporation, Dec. 1, 1944. 

Div. 15-353-M3 


BIBLIOGRAPHY 


477 


305. Tungar Rectifier Bulbs as Noise Generators, Stuart 

Ballantine, Report 1176-1, Project RP-311, Ballantine 
Laboratories, Feb. 11, 1944. Div. 15-343. 22-Ml 

306. Use of Transformer Coupling with Gas-Tube Noise 

Sources, Stuart Ballantine and Edmund Osterland, 
Report 1176-2, Project RP-311, Ballantine Labora- 
tories, June 1, 1944. Div. 15-343.242-M5 

307. Final Report on Noise Source Investigations at Ballantine 
Laboratories, Edmund Osterland, Report 1176-3, Project 
RP-311, Ballantine Laboratories, Aug. 1, 1944. 

Div. 15-343.243-M3 

308. Final Report on Prototype Model Production {Pad), E. 

Hoffman, Report 1179-1, Midwest Radio Corporation, 
Dec. 13, 1944. Div. 15-321. 12-M5 

309. The Development of Low Power Continuously Tuned 
Oscillators Operating in the X and S Bands {The ZK48 
and 2K49 Vacuum Tubes), A. L. Samuel and J. W. 
Clark, Report 1222-1, Project RP-332, Bell Telephone 
Laboratories, Feb. 28, 1945. 

Div. 15-352-M2 

310. The Final Report on the Development of Low Power 

Continuously T uned Oscillators Operating in the X and S 
Bands {The 2K48 and 2K49 Vacuum Tubes), A. L. 
Samuel, Report 1222-2, Projects RP-439, NS-394.01, 
and NA-156, Bell Telephone Laboratories, Sept. 28, 
1945. Div. 15-352-M3 

311. AN/ARQ-13, 500 Watt Amplifier for AN j ARQ-10 
Equipment, C. R. Muller and P. Sokoloff, Report 1275-1, 
Projects RP-200 and NS-128, Federal Telephone and 
Radio Laboratories, Mar. 25, 1946. 

Div. 15-321.21-Ml 

312. Preliminary Antenna Measurements on a Model of 

Hs-293 Glider Bomb, L. K. Findley, Report 1305-1, 
Project RP-382, Airborne Instruments Laboratory, Apr. 
24, 1944. Div. 15-332-Ml 

313. Shipboard Jamming Equipment Type MAS, R. F. 

Schulz, D. M. Miller, and E. W. Adams, Jr., Report 
1305-3, Project RP-395, Airborne Instruments Labora- 
tory, Jan. 2, 1945. Div. 15-263-M3 

314. Analysis of the Radio Control Mechanism of the German 

BlVb Tank, Otto H. Schmitt, Report 1305-4, Project 
RP-384, Airborne Instruments Laboratory, Jan. 10, 
1945. Div. 15-831-Ml 

315. Handbook of Instructions for MAS, Report 1305-5, 

Project RP-395, Airborne Instruments Laboratory, 
Feb. 12, 1945. Div. 15-263-M5 

316. Handbook of Instructions Magnetic Tape Recorder, Serial 

4, 5 and 6, Report 1305-7, Project RP-361, Airborne 
Instruments Laboratory, Apr. 4, 1945. 

Div. 15-263.1-Ml 

317. Handbook of Instructions A udio Oscillator 0-28 1 A RQ-11, 

Report 1305-8, Project RP-419a, Airborne Instruments 
Laboratory, Mar. 19, 1945. Div. 15-321. 22-Ml 

318. Handbook of Instructions Magnetic Tape Recorder, Serial 

1, 2 and 3, Report 1305-9, Projects RP-361, SC-98.07, 
and NA-109, Airborne Instruments Laboratory, May 5, 
1945. Div. 15-263.1-M2 

319. Antenna Switching Unit CLU-24314, Norman E. Klein 

and E. W. Adams, Jr., Report 1305-10, Projects RP- 
402a and NS-310, Airborne Instruments Laboratory, 
Apr. 17, 1945. Div. 15-372.1-M3 


920. Automatic Search Jammer, Broom, R. F. Schulz and 
E. W. Adams, Jr., Report 1305-11, Projects RP-359, 
SC-98.07, and NA-109, Airborne Instruments Labora- 
tory, Apr. 21, 1945. Div. 15-41 1-M4 

321. Jamming Tests of Frequency- Modulated Radio Altim- 
eters, Judson Mead, Report 1305-12, Projects RP-334 
and NS-393.05, Airborne Instruments Laboratory, Apr. 

30, 1945. Div. 15-261-M2 

322. AN /GRQ-1 Jamming Equipment, Orrin W. Towner, 
Jay W. Wright, P. S. Carter, and E. W. Adams, Report 
1305-13, Projects RP-420a and SC-95.12, Airborne 
Instruments Laboratory, May 31, 1945. 

Div. 15-263-M6 

323. Handbook of Instructions for R-21 / ARQ-11, Radio 
Receiver, Report 1305-14, Projects RP-419a, and SC- 
95.14, Airborne Instruments Laboratory, June 30, 1945. 

Div. 15-321. 23-M2 

324. Handbook of Instructions for PP-130/ ARQ-11, Rectifier 

and C-187 / ARQ-11 Control Unit, Report 1305-15, 
Projects RP-419a and SC-95.14, Airborne Instruments 
Laboratory, June 30, 1945. Div. 15-321. 23-M3 

325. Peter Pan Jamming System and Magnetic Tape Record- 

ers, Reuben A. Isberg and E. W. Adams, Jr., Report 
1305-16, Projects RP-361, SC-98.07, NA-109, and NS- 
391.02, Airborne Instruments Laboratory, Aug. 31, 
1945. Div. 15-263.1-M3 

326. AN/SRQ-1 Multi-Channel Jamming Equipment, Otto 
H. Schmitt, R. G. Madsen, G. D. Sullivan, and E. W. 
Adams, Jr., Report 1305-17, Projects RP-389, NA-109, 
and NS-395.04, Airborne Instruments Laboratory, Aug. 

31, 1945. Div. 15-263.M7 

327. AN/ ARQ-11 and AN /SRQ-11 {XN-1) Jamming Equip- 
ment, J. N. Fricker, Otto H. Schmitt, H. W. DeWeese, 
R. R. Yost, C. F. Noyes, and A. C. Weid, Report 
1305-18, Projects RP-419a and SC-95.14, Airborne 
Instruments Laboratory, Aug. 31, 1945. 

Div. 15-263-M8 

328. Antenna Transfer Switch, Norman E. Klein and Lyman 

C. Ihrig, Report 1305-19, Projects RP-402b and NS- 
395.08, Airborne Instruments Laboratory, Aug. 31, 
1945. Div. 15-372.1-M4 

329. Automatic Search Jammer, Beagle, W. I. L. Wu, Report 
1305-20, Projects RP-360, SC-98.07, and NA-109, Air- 
borne Instruments Laboratory, Aug. 31, 1945. 

Div. 15-41 1-M5 

330. Panoramic Receiver, Panther, Wilmer C. Anderson and 

Arthur C. Weid, Report 1305-21, Projects RP-363, 
SC-98.07, and NA-109, Airborne Instruments Labora- 
tory, Aug. 31, 1945. Div. 15-31 1.4-Ml 

331. Jamming Tests on AN / APG-4 Aircraft Radar Equip- 
ment, Judson Mead, Report 1305-22, Project RP-334, 
Airborne Instruments Laboratory, Aug. 31, 1945. 

Div. 15-221. 21-M8 

332. Signal Repeating Jammer, Piano, Otto H. Schmitt, 
Report 1305-23, Projects RP-362, SC-98.07, and NA- 
109, Airborne Instruments Laboratory, Dec. 14, 1945. 

Div. 15-41 1-M6 

333. Mobile Transmitting System, R. F. Schulz and Arthur C. 
Weid, Report 1305-29, Projects RP-117c and SC-98.09, 
Airborne Instruments Laboratory, Feb. 28, 1946. 

Div. 15-402.4-M2 


478 


BIBLIOGRAPHY 


334. Gear Reduction Unit, T. F. Tomlines, 1305-TM-l, 

Project RP-419a, Airborne Instruments Laboratory, 
Mar. 27, 1945. Div. 15-321. 23-Ml 

335. R-F Dummy Load, Otto H. Schmitt, 1305-TM-2, Air- 
borne Instruments Laboratory, Aug. 31, 1945. 

Div. 15-521. 3-M3 

336. 15 kw Communications Jammer AN / MRT-1 Modifica- 

tion Kit for AN/ MRT-1 MX255/ MRT-1, Joseph T. 
Thwaites, Report 1309, 1310-1, Projects RP-356A and 
SC-95.03, Westinghouse Electric and Manufacturing 
Company, Apr. 14, 1945. Div. 15-402. 2-M8 

337. Development of 1000 Watt Tunable Magnetron for S- 

Band, W. G. Wagener, Report 1357-1, Projects RP- 
158b and SC-94.25, Litton Engineering Laboratories, 
Sept. 30, 1945. Div. 15-341. 4-M6 

338. Stopwatch, Edward Ruth III, Report 1428-1, Projects 

RP-263a, NS-203, and NS-395.02, Erco Radio Labora- 
tories, Dec. 13, 1945. Div. 15-402. 3-M2 

339. Preliminary Instruction Manual for AN / URQ-1, 1428-2, 

Erco Radio Laboratories. Div. 1 5-402. 3-M3 

340. Development of Two 1 kw CW Tunable Magnetrons, A. K. 

Wing, Jr., A. S. Vanderhoof, P. 1. Corbell, and H. R. 
Jacobus, Report 1430-1, Projects RP-158C and SC- 
94.25, Federal Telephone and Radio Corporation, Sept. 
29, 1945. Div. 15-341.4-M5 

341. Program of Investigation in Connection with the Deception 

of High Frequency Japanese Direction Finders, H. 
Busignies, Report 1458-1, Projects RP-445 and SC- 
95.16, Federal Telephone and Radio Laboratories, June 
12, 1945. Div. 15-211. 23-M6 

342. Aircraft Radio Direction Finding Equipment, H. Busig- 
nies, Trevor H. Clark, and Henry B, Scarborough, 
Report 1458-2, Projects RP-444 and SC-97.06, Federal 
Telephone and Radio Laboratories, Sept. 29, 1945. 

Div. 15-313. 11-M2 

343. Fundamentals of Radar Anti- Jamming, Report of AJ 

Practices Panel, HB-1, MIT Radiation Laboratory and 
Naval Research Laboratory. Div. 15-222-Ml 

344. Antennas for Radio Countermeasures — Part II, Bibliog- 
raphy of RCM Antenna Information, Robert Serrell, 
HB-2s, Columbia Broadcasting System, Mar. 15, 1945. 

Div. 15-330-M2 

345. Communications Countermeasures [Part II, Estimating 

the Performance of Radio Telephone Jamming Sys- 
tems], J. W. Emling, HB-4, Bell Telephone Labora- 
tories, Feb. 1, 1945. Div. 15-21 1-Ml 

Radio Communications Countermeasures [Part III, Esti- 
mating the Performance of Radio Telegraph Jamming 
Systems], E. W. Borden, HB-4, Bell Telephone Labora- 
tories, Feb. 15, 1946. Div. 15-21 1-M2 

346. The 884 Gas Triode as a Noise Source, J. D. Cobine, 

411-TM-l, Harvard University, Radio Research Lab- 
oratory, Sept. 22, 1943. Div. 15-343.242-Ml 

347. A-1700 Jamming Signal Generator, Ralph Hoglund, 
411-TM-2, Project RP-191, Harvard University, Radio 
Research Laboratory, Nov. 2, 1943. Div. 15-620-Ml 

348. Noise Output of the FG178A Thyratron in the Range 
100 kc-9 Me, J. D. Cobine, Technical Memorandum 
411-3, Project RP-187, Harvard University, Radio Re- 
search Laboratory, Dec. 10, 1943. 


349. Tentative Specifications for Test Oscillator A2651Y to Go 

with AN / APR-5 and AN / APR-6 Receivers, James H. 
Eldredge and R. B. Holt, 411-TM-4, Project RP-292, 
Harvard University, Radio Research Laboratory, Oct. 
9, 1943. Div. 15-511-M2 

350. A Wide-Band R-F Sweep Generator, C. B. Clark and 
John P. Woods, 411-TM-5, Project RP-110, Harvard 
University, Radio Research Laboratory, Mar. 15, 1944. 

Div. 15-512-M5 

351. Specifications for the D1203 Panoramic Spectrum Ana- 

lyzer, W. B. Caufield, 411-TM-6, Project RP-175, 
Harvard University, Radio Research Laboratory, Oct. 
13, 1943. Div. 15-513-M2 

352. D1203 Panoramic Spectrum Analyzer, R. A. Soderman, 
411-TM-6A, Project RP-175, Harvard University, 
Radio Research Laboratory, July 13, 1944. 

Div. 15-513-M5 

353. High Power Resnatron Jamming Transmitters Prelimin- 
ary Specifications for Mobile Units, W. W. Salisbury, 
411-TM-7, Project RP-lOO, Harvard University, Radio 
Research Laboratory, May 27, 1943. Div. 15-323-Ml 

354. TheA741 Test Transmitter, Robert B. Barnes, 411-TM-8, 

Project RP-147, Harvard University, Radio Research 
Laboratory, May 31, 1943. Div. 15-517-Ml 

355. The A2107 Test Buzzer, H. T. O’Neill, 411-TM-9, 

Project RP-147, Harvard University, Radio Research 
Laboratory, May 31, 1943. Div. 15-517-M2 

356. Notes on the BC-1255 {A) Heterodyne Frequency Meter, 
John F. Byrne, 411-TM-lO, Project RP-294, Harvard 
University, Radio Research Laboratory, June 2, 1943. 

Div. 15-514-Ml 

357. Note on Barrage Jamming with Special Reference to Use 

of RC-156 and AN/APQ-9 Transmitters, Warren D. 
White, 411-TM-ll, Projects RP-165 and RP-166, 
Harvard University, Radio Research Laboratory, July 
9, 1943. Div. 15-322. 121-Ml 

358. Preliminary Specifications for AN/APQ-1 Test Equip- 

ment, John N. Dyer, 411-TM-12, Projects RP-289 and 
RP-290, Harvard University, Radio Research Labora- 
tory, Oct. 13, 1943. Div. 15-401. 1-M2 

359. Preliminary Specifications for B3000 Heterodyne Fre- 

quency Meter, George Evans, 411-TM-13, Project RP- 
245, Harvard University, Radio Research Laboratory, 
Aug. 23, 1943. Div. 15-514-M2 

360. Methods of Selecting and Setting the Frequency of RC-156 
and AN/APQ-9 Carpet Transmitters, John N. Dyer, 
411-TM-14, Projects RP-165 and RP-166, Harvard 
University, Radio Research Laboratory, July 9, 1943. 

Div. 15-322. 121-M2 

361. The D1600 Variable Range Motor Drive for AN/ APR-1 

Receiver, Joseph M. Pettit, 411-TM-15, Project RP-141, 
Harvard University, Radio Research Laboratory, Aug. 
5, 1943. Div. 15-311. 121-Ml 

362. Preliminary Specifications for B2800 High Power Dina 

Amplifier, John B. Caraway, 411-TM-16, Project RP- 
218, Harvard University, Radio Research Laboratory, 
Aug. 4, 1943. Div. 15-322.21-Ml 

363. Losses in Various Transmission Lines at Several Fre- 
quencies, L. T. Slocum, 411-TM-17, Harvard University, 
Radio Research Laboratory, Aug. 16, 1943. 

Div. 15-371-Ml 


Div. 15-343.23-Ml 


BIBLIOGRAPHY 


479 


364. The F2305 Transmitter Output Indicator, .Warren D. 
White, 411-TM-18, Project RP-290, Harvard Univer- 
sity, Radio Research Laboratory, July 30, 1943. 

Div. 15-524-Ml 

365. Modifications on the RC-183 Mandrel, E. L. Plotts, 
411-TM-19, Project RP-163, Harvard University, Radio 
Research Laboratory, Aug. 6, 1943. 

Div. 15-322. 14-M2 

366. Energy Spectrum of the B2000 RC-183, Mandrel Trans- 

mitter, R. E. Reid and P. P. Robbiano, 411-TM-19A, 
Project RP-163, Harvard University, Radio Research 
Laboratory, Sept. 24, 1943. Div. 15-322. 14-M3 

367. The B3200-B2900 Dina-Dinamate Transceiver, Harvey 

Kees, 411-TM-20, Projects RP-250 and RP-267, Har- 
vard University, Radio Research Laboratory, Feb. 9, 
1944. Div. 15-321.1 1-M4 

368. Tests of British Boozer {Model R-1618), Seymour B. 

Cohn, 411-TM-21, Harvard University, Radio Research 
Laboratory, Jan. 4, 1944. Div. 15-312. 2-Ml 

369. Wide-Band Transformer from an Unbalanced to a Bal- 

anced Line, Eugene Fubini, 411-TM-22, Project RP-107, 
Harvard University, Radio Research Laboratory, Oct. 
28, 1943. Div. 15-381. 1-M3 

370. A Study of a Particular Scheme for Communications 

Jamming, W. R. Rambo, 411-TM-23, Project RP-197, 
Harvard University, Radio Research Laboratory, Nov. 
1, 1943. Div. 15-21 1.22-Ml 

371. Equivalent Point Antennas of Constant Current Epoch, 
Donald Foster, 411-TM-24, Project RP-107, Harvard 
University, Radio Research Laboratory, Nov. 5, 1943. 

Div. 15-333.22-Ml 

372. Preliminary Report on Propeller Modulation Detection, 
D. R. Scheuch, 411-TM-25, Project RP-213, Harvard 
University, Radio Research Laboratory, Nov. 3, 1943. 

Div. 15-241.4-Ml 

373. Spectra Due to Simultaneous Amplitude and Frequency 

Modulation, T. S. Kuhn and L. Hoffman, 411-TM-26, 
Project RP-217, Harvard University, Radio Research 
Laboratory, Nov. 24, 1943. Div. 15-221. 12-M2 

374. Jammer Frequency Setting, Matthew T. Lebenbaum, 
411-TM-27, Project RP-327, Harvard University, Radio 
Research Laboratory, Nov. 9, 1943. Div. 15-323-M3 

375. Concerning the Use of Metallized Ropes as Confusion 
Reflectors, Eugene Fubini and Morton Hamermesh, 
411-TM-28, Project RP-257, Harvard University, Radio 
Research Laboratory, Oct. 27, 1943. 

Div. 15-241. 2-M2 

376. On the Response of a Detector to Jittered Slow FM, John 
H. Van Vleck, 411-TM-29, Project RP-182, Harvard 
University, Radio Research Laboratory, Nov. 19, 1943. 

Div. 15-211. 31-M3 

377. Notes on the Velocity of Radio Waves in a Coaxial Line, 
W. W. Salisbury, 411-TM-30, Harvard University, 
Radio Research Laboratory, Aug. 15, 1944. 

Div. 15-371. 2-Ml 

378. The Jamming Effectiveness of a Gas Tube Noise Source 

Exhibiting Oscillations, D. A. Peterson, 411-TM-31, 
Project RP-186, Harvard University, Radio Research 
Laboratory, Nov. 22, 1943. Div. 1 5-343. 242-M3 

379. The Useftdness of Long Persistence Screens as a Counter- 
measure against Window, E. R. Brill, 411-TM-32, 


Project RP-318, Harvard University, Radio Research 
Laboratory, Nov. 26, 19431 Div. 15-241-M4 

380. Suggested Anti-Jam Video Amplifiers for SCR-717-B, 
J. H. Woodruff, 411-TM-33, Harvard University, Radio 
Research Laboratory, Jan. 19, 1944. 

Div. 15-222. 1-M2 

381. A Preliminary Report on Split-Can Antennas for Hori- 

zontal Polarization, Andrew Alford and Peter L. Har- 
bury, 411-TM-34, Harvard University, Radio Research 
Laboratory, Dec. 13, 1943. Div. 1 5-332. 14-Ml 

382. The M-4500 Spinner for the M-2300, M-2600, M-3000, 

and M-4100 Systems, Peter L. Harbury, 411-TM-35, 
Project RP-271, Harvard University, Radio Research 
Laboratory, Nov. 29, 1944. Div. 15-331. 2-Ml 

383. Noise Output of RCA 2D21 Miniature Gas Tetrode, in the 

Range 100 Kc to 9 Me, J. D. Cobine, 411-TM-36, Project 
RP-186, Harvard University, Radio Research Labora- 
tory, Jan. 11, 1944. Div. 15-343. 243-Ml 

384. Noise Generated by the Sylvania 2C4 and 6D4 Miniature 
Gas Triodes, in the Frequency Range 100 Kc to 5 Me, J. D. 
Cobine, 411-TM-38, Project RP-187, Harvard Univer- 
sity, Radio Research Laboratory, Feb. 8, 1944. 

Div. 15-343.241-Ml 

385. Noise Generated by the Sylvania 2C4 and 6D4 Miniature 
Gas Triodes {in the Frequency Range 100 Kc-9 Me), J. D. 
Cobine, 411-TM-38A, Project RP-187, Harvard Univer- 
sity, Radio Research Laboratory, Mar. 21, 1944. 

Div. 15-343.241-M2 

386. Z-1600, RF Power Indicator, R. R. Rhiger and R. B. 
Monroe, 411-TM-39, Harvard University, Radio Re- 
search Laboratory, Jan. 11, 1944. 

Div. 15-521.3-Ml 

387. Notes on a Common-Grid Reactance Tube Circuit, W. R. 
Rambo, 411-TM-40, Project RP-203, Harvard Univer- 
sity, Radio Research Laboratory, Jan. 15, 1944. 

Div. 15-345-Ml 

388. A Common-Grid Reactance-Tube Circuit at Ultra-High 
V Frequencies, J. W. Kearney and W. R. Rambo, 411-TM- 

40A, Project RP-203, Harvard University, Radio Re- 
search Laboratory, Apr. 15, 1944. Div. 15-345-M3 

389. Note on the Equivalent Forms for the Mean Output of an 
Unbiased Linear Rectifier Subject to Noise, David Mid- 
dleton, 411-TM-41, Project RP-181, Harvard Univer- 
sity, Radio Research Laboratory, Jan. 15, 1944. 

Div. 15-221. 1-M3 

390. Broad^Band Lobe- Switching Antenna, Donald Foster, 
411-TM-42, Project RP-107, Harvard University, Radio 
Research Laboratory, Feb. 4, 1944. 

Div. 15-333.51-Ml 

391. The D514 I-F Amplifier for the AN/ APR-4 Receiver, 
Joseph M. Pettit, 411-TM-43, Harvard University, 
Radio Research Laboratory, Feb. 7, 1944. 

Div. 15-311.123-Ml 

392. The R1800 Recording Search Receiver, R. C. Raymond, 
411-TM-44, Project RP-286, Harvard University, Radio 
Research Laboratory, Feb. 9, 1944. 

Div. 15-31 1.3-M2 

393. RCM Test Equipment Summary as of January 1, 1944, 
John F. Byrne, 411-TM-45, Harvard University, Radio 
Research Laboratory, Jan. 14, 1944. 


Div. 15-510-Ml 


480 


BIBLIOGRAPHY 


394. Preliminary Specifications for the M2300 Direction Find- 

ing System, Arthur Dome, 411-TM-46, Project RP-298, 
Harvard University, Radio Research Laboratory, Nov. 
12, 1943. Div. 15-313.15-Ml 

395. Low Frequency Spark-Over in Air at Low Pressures, John 
P. Woods, 411-TM-47, Project RP-178, Harvard Uni- 
versity, Radio Research Laboratory, Jan. 20, 1944. 

Div. 15-323-M4 

396. Preliminary Specifications for B3400 Dina Amplifier, 
John B. Caraway, 411-TM-48, Project RP-329, Harvard 
University, Radio Research Laboratory, Oct. 26, 1943, 

Div. 15-322.21-M2 

397. Preliminary Description of the D1500 {1000 to 3300 Me) 
Tuner for Search Receivers, Joseph M. Pettit, 411-TM- 
49, Project RP-141, Harvard University, Radio Re- 
search Laboratory, Feb. 2, 1944. Div. 15-311. 21-M4 

398. Preliminary Description and Specifications of D1800 
Recorder for Search Receivers, H. E. Overacker and 
Joseph M. Pettit, 411-TM-50, Project RP-276, Harvard 
University, Radio Research Laboratory, Nov. 27, 1943. 

Div. 15-311. 31-Ml 

399. Specifications for a Recorder for Search Receivers, Re- 

ceiver Design Committee, 411-TM-50A, Project RP- 
276, Harvard University, Radio Research Laboratory, 
Feb. 2, 1944. Div. 15-31 1.31-M2 

400. D-1800 Recorder, AN / APA-23, H. E. Overacker, 411- 
TM-50B, Project RP-276, Harvard University, Radio 
Research Laboratory, May 11, 1944. 

Div. 15-311. 31-M3 

401. A/J Doctoring of FD Radar, Richard S. O’Brien, 411- 
TM-51, Project RP-214, Harvard University, Radio 
Research Laboratory, Feb. 2, 1943. 

Div. 15-222. 1-Ml 

402. B3100 Double Peaking Device, Leonard A. Mayberry, 
411-TM-52, Project RP-293, Harvard University, Radio 
Research Laboratory, Nov. 29, 1943. 

Div. 15-322.21-M3 

403. M2201 Antenna, C. Milton Daniell, 411-TM-53, Project 

RP-138, Harvard University, Radio Research Labora- 
tory, Dec. 3, 1943. Div. 15-332. 11-Ml 

404. The M2202 Antenna, C. Milton Daniell, 411-TM-54, 

Project RP-279, Harvard University, Radio Research 
Laboratory, Feb. 16, 1944. Div. 15-332. 11-M2 

405. Comparative Field Intensity Response of M2409 Cone 
Dipole and M801 Single Cone Antennas, E. L. Bock, 
411-TM-55, Project RP-138, Harvard University, Radio 
Research Laboratory, June 23, 1944. 

Div. 15-331.31-M3 

406. Plug-in A / J High-Pass Filter, H. O. Anger, 411-TM-56, 

Project RP-224, Harvard University, Radio Research 
Laboratory, Feb. 18, 1944. Div. 15-222. 1-M4 

407. Summary of RRL Receiver Projects December 1, 1943, 
Joseph M. Pettit, 411-TM-57, Harvard University, 
Radio Research Laboratory, Feb. 2, 1944. 

Div. 15-310-Ml 

408. Radio Research Laboratory Transmitter Situation, George 
E. Hulstede, 411-TM-58, Harvard University, Radio 
Research Laboratory, Jan. 29, 1944. 

Div. 15-320-Ml 

409. Energy Spectrum of the B2200 AN / APT-1, Dina Trans- 
mitter, P. P. Robbiano and R. E. Reid, 411-TM-59, 


Project RP-309, Harvard University, Radio Research 
Laboratory, Sept. 24, 1943. Div. 1 5-322. 13-Ml 

410. RRL Magnetron Program as of December 1, 1943, W. G. 

Dow, 411-TM-60, Harvard University, Radio Research 
Laboratory, Feb. 2, 1944. Div. 15-341-Ml 

411. The C2 100 Airborne Direction Finder, John W. Christen- 
sen, 411-TM-61, Project RP-298, Harvard University, 
Radio Research Laboratory, Feb. 7, 1944. 

Div. 15-313.14-Ml 

412. C2100D Airborne Direction Finder, John W. Christen- 
sen, 411-TM-61A, Project RP-298, Harvard University, 
Radio Research Laboratory, Mar. 22, 1944. 

Div. 15-313.14-Ml 

413. The C2100 Airborne Direction Finder, John W. Christen- 
sen, 411-TM-61B, Project RP-298, Harvard University, 
Radio Research Laboratory, May 23, 1944. 

Div. 15-313.14-Ml 

414. Tests of AN / APA-24 {C2 100-Setter) Airborne Direction- 
finding Equipment, R. L. Hammett and F. M. Wright- 
son, 411-TM-61C, Project RP-298, Harvard University, 
Radio Research Laboratory, June 21, 1944. 

Div. 15-313.14-M2 

415. The F4100 Training Oscillator, Elton Barrett, 411-TM- 
62, Project RP-348, Harvard University, Radio Re- 
search Laboratory, Feb. 9, 1944. 

Div. 15-610. 1-Ml 

416. The U400 Noise Tube Tester, C. D. Jeffries, 411-TM-63, 

Project RP-266, Harvard University, Radio Research 
Laboratory, Feb. 8, 1944. Div. 15-515-M2 

417. The R807 Low-Pass Filter, Seymour Cohn, 411-TM-64, 

Project RP-287, Harvard University, Radio Research 
Laboratory, Mar. 17, 1944. Div. 15-361. 1-Ml 

418. Notes on the Wide Band Modulation of Coaxial Line 
Oscillators Using Lighthouse Triodes, R. R. Webster, 
411-TM-65, Project RP-305, Harvard University, Radio 
Research Laboratory, Mar. 10, 1944. 

Div. 15-353-M2 

419. Operation of RCA A2212 in a Coaxial Cavity Oscillator, 
R. L. Henkel, 411-TM-66, Harvard University, Radio 
Research Laboratory, Feb. 4, 1944. 

Div. 15-351. 1-M3 

420. M3100 Homing Device, Peter L. Harbury, 411-TM-67, 

Project RP-298, Harvard University, Radio Research 
Laboratory, Feb. 1, 1944. Div. 15-313. 15-M 2 

421. AN / ARQ-8 Equipment as a Countermeasure for German 

Guided Missiles, Oswald G. Villard, Jr., and Barbara 
Bacorn, 411-TM-68, Projects RP-250 and RP-267, 
Harvard University, Radio Research Laboratory, May 
16, 1944. Div. 15-263-Ml 

422. One-Sided Clipping of the 6D4 Spectrum, P. S. Jastram, 
411-TM-69, Project RP-187, Harvard University, Radio 
Research Laboratory, July 27, 1944. 

Div. 15-343.241-M5 

423. High Frequency Calorimeter Wattmeter, J. Gregg Ste- 

phenson and R. L. Henkel, 411-TM-70, Project RP-306, 
Harvard University, Radio Research Laboratory, Mar. 
28, 1944. Div. 15-521. 12-Ml 

424. AN / APR6 Installation Information as of February 19, 

1944, Walter G. Wadey, 411-TM-71, Project RP-286, 
Harvard University, Radio Research Laboratory, Feb. 
19, 1944. Div. 15-31 1.125-Ml 


BIBLIOGRAPHY 


481 


425. D1901 Modification Kit for I-F Gain Control and A-V-C 
Switch for SCR-587 and Arc-1 Receivers, Joseph M. 
Pettit, 411-TM-73, Harvard University, Radio Re- 
search Laboratory, Feb. 14, 1944. Div. 15-31 1.111-M2 

426. D1902 Motor-Noise Filter for TU-57B and TU-58B 

Tuning Units for SCR-587 Receiver, Joseph M. Pettit, 
411-TM-74, Harvard University, Radio Research Lab- 
oratory, Feb. 14, 1944. Div. 15-31 1.21-M5 

427. D1903 Conversion for Operation of Arc- 1 Receiver from a 

28-Volt Power Source, Joseph M. Pettit, 411-TM-75, 
Harvard University, Radio Research Laboratory, Feb. 
18, 1944. Div. 15-311. 111-M3 

428. A Low-Power Spot- Jamming Transmitter A 3500, W. R. 
Rambo, 411-TM-76, Project RP-203, Harvard Univer- 
sity, Radio Research Laboratory, Mar. 27, 1944. 

Div. 15-321. 13-Ml 

429. AS-44/APR {A2602) Antenna for the AN /APR-5 
(A 2600) Microwave Receiver, 1000 to 3100 Me, H. C. 
Singleton, 411-TM-77, Project RP-135, Harvard Uni- 
versity, Radio Research Laboratory, Feb. 25, 1944. 

Div. 15-331. 112-M2 

430. The F-3701 Dipole and Corner Reflector Antenna {450 to 

720 Me), H. C. Singleton, 411-TM-78, Project RP-138, 
Harvard University, Radio Research Laboratory, Feb. 
25, 1944. Div. 15-332. 21-Ml 

431. AS-29 / APR {M2 101) Broadband Cone Antenna {300 to 

3300 Me), H. C. Singleton, 411-TM-79, Project RP-138, 
Harvard University, Radio Research Laboratory, Feb. 
28, 1944. Div. 15-331. 112-M3 

432. AS-56/ APR {M2408) Shipboard Dipole Antenna, 75 to 

300 Me, H. C. Singleton, 411-TM-80, Project RP-138, 
Harvard University, Radio Research Laboratory, Feb. 
28, 1944. Div. 15-331.31-Ml 

433. AS-56/ SPR {M2409) Shipboard Cone Dipole Antenna, 
H. C. Singleton, 411-TM-81, Project RP-138, Harvard 
University, Radio Research Laboratory, Feb. 29, 1944. 

Div. 15-331.31-M2 

434. M-2508 Ground Based Corner Reflector Antenna, 90 to 

150 Me, H. C. Singleton, 411-TM-82, Project RP-138, 
Harvard University, Radio Research Laboratory, Feb. 
25, 1944. Div. 15-332. 24-Ml 

435. M-2511 Ground Based Corner Reflector Antenna, 150 to 

210 Me, H. C. Singleton, 411-TM-83, Project RP-138, 
Harvard University, Radio Research Laboratory, Feb. 
28, 1944. Div. 15-332. 24-M2 

436. Temporary Conversion of Sickles Tuning Units TU57B 
and TU58B to Sector Sweep, Robert R. Buss, 411-TM- 
84, Project RP-141, Harvard University, Radio Re- 
search Laboratory, Feb. 24, 1944. Div. 15-311.21-M6 

437. Frequency Bands of Loaded and Unloaded Resonant 

Sections of Line, Peter J. Sutro, 411-TM-85, Project 
RP-107, Harvard University, Radio Research Labora- 
tory, July 26, 1944. Div. 15-371-M4 

438. A/J Practice for Fire-Control Radar Systems, H. O. 
Anger, 411-TM-87, Project RP-224, Harvard Univer- 
sity, Radio Research Laboratory, Mar. 23, 1944. 

Div. 15-222.1-M6 

439. A Rapid Fastener for Waveguides, Walter G. Wadey, 
411-TM-88, Project RP-286, Harvard University, Radio 
Research Laboratory, July 22, 1944. 


440. Preliminary Test Report on the RC-156 as a Spot Jammer, 
E. F. Vidro, 411-TM-89, Harvard University, Radio 
Research Laboratory, Feb. 8, 1944. 

Div. 15-322.124-M3 

441. Reactance Switching: A Method of Producing Wide- 
Band Frequency Modulation, J. W. Kearney, 411-TM- 
90, Project RP-203, Harvard University, Radio Re- 
search Laboratory, Mar. 28, 1944. Div. 15-221. 12-M4 

442. Radar Echoes from Angels Obtained at Florosa, H. C. 
Pollock, 411-TM-91, Project RP-258, Harvard Univer- 
sity, Radio Research Laboratory, Mar. 27, 1944. 

Div. 15-241.3-M2 

443. Airborne Antennas for AN / APR-1, C. Milton Daniell 
and M. J. White, 411-TM-92, Project RP-144, Harvard 
University, Radio Research Laboratory, Mar. 31, 1944. 

Div. 15-331. 11-Ml 

444. Photographs and Characteristics of the M801 Antenna 

Assembly for the RC-160 {CllOO) Autosearch Receiver, 
C. Milton Daniell, 411-TM-93, Project RP-138, Har- 
vard University, Radio Research Laboratory, Mar. 31, 
1944. Div. 15-331.1 1-M2 

445. Mounting of a Hewlett-Packard Audio Oscillator in a 

Standard Aircraft Rack, John H. Jasberg, 411-TM-94, 
Project RP-315, Harvard University, Radio Research 
Laboratory, Apr. 15, 1944. Div. 15-512. 1-Ml 

446. Preliminary Operating Instructions for Y-700 Bandwidth 
Adjustment Indicator, Leonard A. Mayberry, 411-TM- 
95, Project RP-293, Harvard University, Radio. Re- 
search Laboratory, Feb. 10, 1944. Div. 15-314.21-Ml 

447. Test Report {Test Laboratory) F-2500 Carpet III, R. B. 

Monroe and R. R. Rhiger, 411-TM-96, Project RP-166, 
Harvard University, Radio Research Laboratory, Apr. 
14, 1944. Div. 15-322. 124-M4 

448. Type P523-A Oscillator Tentative Specifications, A. P. G. 
Peterson, 411-TM-97, Project RP-195, Harvard Uni- 
versity, Radio Research Laboratory, June 18, 1943. 

Div. 15-511-Ml 

449. The R-1700 Wide Band Regenerative Circuit, R. C. Ray- 

mond and Seymour B. Cohn, 411-TM-98, Project RP- 
117, Harvard University, Radio Research Laboratory, 
Apr. 3, 1944. Div. 15-383-M3 

450. Jamming the German FGIOIA, FG103 Radio Altimeters, 
Donald Foster, 411-TM-99, Project RP-299, Harvard 
University, Radio Research Laboratory, Mar. 22, 1944. 

Div. 15-261-Ml 

451. Reflection of Long Ropes, Felix Bloch and Morton 
Hamermesh, 411-TM-lOO, Project RP-257, Harvard 
University, Radio Research Laboratory, Apr. 14, 1944. 

Div. 15-241. 2-M3 

452. Reflection of Long Ropes, Felix Bloch and M. Phillips, 
411-TM-lOOA, Project RP-257, Harvard University, 
Radio Research Laboratory, June 1, 1944. 

Div. 15-241. 2-M3 

453. Cavity Oscillators as Jammers, Robert R. Buss, 411-TM- 
101, Project RP-186, Harvard University, Radio Re- 
search Laboratory, Apr. 20, 1944. 

Div. 15-351. 2-M5 

454. The M-125 75-Megacycle Low-Pass Filter, J. G. C. 
Swinney, Jr., 411-TM-102, Project RP-306, Harvard 
University, Radio Research Laboratory, Apr. 24, 1944. 

Div. 15-362-Ml 


Div. 15-371. 1-Ml 


482 


BIBLIOGRAPHY 


455. 30-Kw Air-Borne Auxiliary High-Voltage DC Power 

Source, W. G. Dow, 411-TM-103, Project RP-321, 
Harvard University, Radio Research Laboratory, Apr. 
24, 1944. Div. 15-391-M2 

456. Practice Jamming Transmitters, E. A. Yunker, 411-TM- 
104, Projects RP-180, RP-323, and RP-348, Harvard 
University, Radio Research Laboratory, Apr. 3, 1944. 

Div. 15-610-Ml 

457. R-F Voltage Regulator, Seymour B. Cohn, 411-TM-105, 

Project RP-306, Harvard University, Radio Research 
Laboratory, Apr. 26, 1944. Div. 15-517-M3 

458. Preliminary Considerations concerning Radar Echoes and 
RCM Parameters in Naval Operations, T. S. Kuhn, 
411-TM-106, Project RP-299, Harvard University, 
Radio Research Laboratory, May 31, 1944. 

Div. 15-221. 11-Ml 

459. Field Tests of L-105 Jamming Signal Generator against 

Mark 8 Fire-Control Radar, W. W. Farley, 411-TM-107, 
Project RP-385, Harvard University, Radio Research 
Laboratory, May 1, 1944. Div. 15-512-M6 

460. Results of Chaff Tests at Florosa December 13 to 20, 1943- 

January 18, 1944, J. Levine, 411-TM-108, Project 
RP-103, Harvard University, Radio Research Labora- 
tory, Apr. 5, 1944. Div. 15-241. 1-M2 

461. Echo Characteristics of Three Reflectors at 565 Me, H. C. 
Pollock, 411-TM-109, Project RP-258, Harvard Uni- 
versity, Radio Research Laboratory, Apr. 1, 1944. 

Div. 15-241. 3-M3 

462. Transmitter, Dina {AN/ APT-1), L. A. Mayberry, 411- 
TM-110, Project RP-309, Harvard University, Radio 
Research Laboratory, May 8, 1944. 

Div. 15-322. 13-M2 

463. R-800 Early Warning Receiver {Zero Catcher II), Sey- 
mour B. Cohn, 411-TM-lll, Project RP-287, Harvard 
University, Radio Research Laboratory, May 0, 1944. 

Div. 15-312.1-M3 

464. A-2651-Y Pulsed Oscillator, R. C. Raymond, 411-TM- 
112, Project RP-292, Harvard University, Radio Re- 
search Laboratory, May 2, 1944. Div. 15-512. 1-M2 

465. The A-2602, A-2608 andA-2612 Cone Antennas, Peter L. 
Harbury, 411-TM-113, Project RP-135, Harvard Uni- 
versity, Radio Research Laboratory, July 13, 1944. 

Div. 15-331. 112-M4 

466. F-3400 Magnetron Transmitter AN /APT-4, 411-TM- 

114, Project RP-338, Office of the Editorial Director, 
Harvard University, Radio Research Laboratory, May 
16, 1944. Div. 15-322.15-Ml 

467. Low-Frequency Noise Spectrum of the 6D4 Gas Triode, 
J. D. Cobine, 411-TM-115, Project RP-187, Harvard 
University, Radio Research Laboratory, May 15, 1944. 

Div. 15-343.241-M3 

468. Low-Frequency Noise Spectrum of the 884 Gas Triode, 
J. D. Cobine, C. J. Gallagher, and P. S. Jastram, 
411-TM-116, Project RP-187, Harvard University, 
Radio Research Laboratory, May 15, 1944. 

Div. 15-343.242-M4 

469. E-512 Detuning Device for Navy Mark 3 and Mark 4 and 
Army SCR-296-A Radars, H. O. Anger and Richard S. 
O’Brien, 411-TM-117, Project RP-224, Harvard Uni- 
versity, Radio Research Laboratory, May 19, 1944. 

Div. 15-222.1-M7 


470. Determination of Relative Power on a Concentric Trans- 

mission Line, C. Milton Daniell, 411-TM-118, Project 
RP-306, Harvard University, Radio Research Labora- 
tory, June 13, 1944. Div. 15-371. M2 

471. Life Tests on RCA 931 A Phototubes, C. J. Gallagher, 
411-TM-119, Project RP-187, Harvard University, 
Radio Research Laboratory, May 31, 1944. 

Div. 15-343.1-M6 

472. AN /APT-5 {XA-2C) and AN /APT-5 Transmitters 

{F-3500), 411-TM-120, Project RP-336, Office of the 
Editorial Director, Harvard University, Radio Research 
Laboratory, July 7, 1944. Div. 1 5-322. 123-Ml 

473. Noise Output of the GL-546, C. J. Gallagher, 411-TM- 
121, Project RP-187, Harvard University, Radio Re- 
search Laboratory, June 5, 1944. 

Div. 15-343.23-M2 

474. M-3203 Antennas, Clare Driscoll, 411-TM-122, Project 

RP-303, Harvard University, Radio Research Labora- 
tory, June 12, 1944. Div. 15-332. 13-Ml 

475. Theory and Applications of Loop Antennas, Donald 
Foster, 411-TM-123, Project RP-107, Harvard Univer- 
sity, Radio Research Laboratory, July 22, 1944. 

Div. 15-333.22-M3 

476. A/J Training Installation for Navy SC Radar, F. P. 
Cowan, 411-TM-124, Project RP-214, Harvard Uni- 
versity, Radio Research Laboratory, June 5, 1944. 

Div. 15-641-Ml 

477. Equivalent Radius of Thin Cylindrical Antennas, Felix 

Bloch and Morton Hamermesh, 411-TM-125, Project 
RP-257, Harvard University, Radio Research Labora- 
tory, June 20, 1944. Div. 15-24L2-M4 

478. The Dependence of the Response of Microwave Chaff on 
Polarization and Angle of Elevation, R. D. Sard, 411- 
TM-126, Project RP-257, Harvard University, Radio 
Research Laboratory, June 22, 1944. 

Div. 15-241. 1-M4 

479. Return Cross Sections from Random Oriented Resonant 

Half-wave Length Chaff, Felix Bloch, Morton Hamer- 
mesh, and M. Phillips, 411-TM-127, Project RP-257, 
Harvard University, Radio Research Laboratory, June 
19, 1944. Div. 15-241. 1-M3 

480. E- 1300- Interference Generator, D. R. Scheuch, 411-TM- 
128, Project RP-313, Harvard University, Radio Re- 
search Laboratory, July 25, 1944. 

Div. 15-620-M4 

481. U -600 Automat, H. E. Overacker, 411-TM-129, Project 

RP-380, Harvard University, Radio Research Labora- 
tory, July 3, 1944. Div. 15-411-M3 

482. A Note on Three Theoretical Expressions for the Charac- 
teristic Impedance of a Shielded Balanced Line, Peter J. 
Sutro, 411-TM-130, Project RP-107, Harvard Univer- 
sity, Radio Research Laboratory, July 7, 1944. 

Div. 15-371. M3 

483. Echoes from Angels at 565 Me Obtained at Florosa, J. 
Levine, 411-TM-131, Project RP-258, Harvard Univer- 
sity, Radio Research Laboratory, July 7, 1944. 

Div. 15-241. 3-M4 

484. Theory of Mode Separation in a Coaxial Oscillator, Peter 
J. Sutro, 411-TM-132, Project RP-107, Harvard Uni- 
versity, Radio Research Laboratory, July 25, 1944. 

Div. 15-372. 2-Ml 


BIBLIOGRAPHY 


483 


485. Balloon-Supported Ropes, H. C. Pollock, 411-TM-133, 

Project RP-257, Harvard University, Radio Research 
Laboratory, June 26, 1944. Div. 15-241. 2-M5 

486. M-4400 High-Gain Antenna, Clare Driscoll, 411-TM- 
134, Project RP-138, Harvard University, Radio Re- 
search Laboratory, Sept. 6, 1944. Div. 15-332. 26-Ml 

487. Survey of Microwave Power Oscillators, F. A. Record, 
411-TM-135, Project RP-295, Harvard University, 
Radio Research Laboratory, Aug. 14, 1944. 

Div. 15-351. 1-M2 

488. Field Tests of Ropes, Arthur W. Tyler, 411-TM-136, 

Project RP-406, Harvard University, Radio Research 
Laboratory, Aug. 1, 1944. Div. 15-241, 2-M6 

489. Notes on the Use of APR 5 Receiver at Frequencies above 

3000 Megacycles, George E. Hulstede, 411-TM-137, 
Project RP-135, Harvard LTniversity, Radio Research 
Laboratory, Aug. 15, 1944. Div. 15-311.124-Ml 

490. Noise Modulation of ZP 597 Magnetron at 150-Watt Out- 

put Level, F. H. Crawford, 411-TM-138, Project RP-295, 
Harvard University, Radio Research Laboratory, Aug. 
1, 1944. Div. 15-341. 2-M2 

491. Noise Modidation of the ZP-594 at 1 Kw Output Power, 

F. H, Crawford, 411-TM-138A, Project RP-295, Har- 
vard University, Radio Research Laboratory, Oct. 2, 
1944. Div. 1 5-341. 4-Ml 

492. A 3-6 Cm Low-Power Oscillator, Ralph H. Hoglund, A. J. 

Yakutis, and J. W. Keuffel, 41 l-TM-139, Project RP- 
286, Harvard University, Radio Research Laboratory, 
Aug. 22, 1944. Div. 15-352-Ml 

493. M2903 Shipborne Antenna, E. L. Bock, 41 l-TM-140, 

Project RP-138, Harvard University, Radio Research 
Laboratory, Oct. 7, 1944. Div. 15-332. 25-Ml 

494. D-1905 Spurious Response Indicator for D-101 and 

D-102 Tuning Units, F. J. Kamphoefner, 41 l-TM-141, 
Project RP-381, Harvard University, Radio Research 
Laboratory, Sept. 12, 1944. Div. 15-31 1.21 -M 7 

495. 5 to 10 Cm Search Antennas for Naval Installations of the 

AN / APR-5 A Receiver, Walter G. Wadey, 411-TM-143, 
Project RP-107, Harvard University, Radio Research 
Laboratory, Sept. 7, 1944. Div. 15-331. 32-Ml 

496. A High Level Noise Generator, John N. Dyer, Report 

411-1, Harvard University, Radio Research Laboratory, 
July 8, 1942. Div. 15-343. 1-Ml 

497. A Study of Jamming of Radar Systems, John F. Byrne 

and Roger J. Pierce, Report 411-2, Project B-500, Har- 
vard University, Radio Research Laboratory, July 6, 
1942. Div. 15-221. 1-Ml 

498. Preliminary Instruction Book B1600 Transmitter, John 
F. Byrne, Report 411-3, Harvard University, Radio 
Research Laboratory, Oct. 16, 1942. Div. 15-322. 16-Ml 

499. Analysis of Window and Related Matters, L. J. Chu, 
Report 411-4, Project A-400, Harvard University, 
Radio Research Laboratory, Oct. 22, 1942. 

Div. 15-241-Ml 

500. Progress Report of the Radio Research Laboratory, Report 

411-5, Harvard University, Radio Research Laboratory, 
Oct. 3, 1942. Div. 15-121-Ml 

501. Operating Instructions for Type DlOl Tuning Unit, 

David B. Sinclair, Report 411-6, Project D-lOO, Har- 
vard University, Radio Research Laboratory, Oct. 15, 
1942. Div. 15-31 1.2 1-Ml 


502. Sideband Energy in a Modulated Wave, Warren D. White, 

Report 411-7, Harvard University, Radio Research 
Laboratory, Nov. 27, 1942. Div. 15-221. 12-Ml 

503. RMS and Average Value of Limited Noise (Appendix to 
Report 7), Warren D. White, Report 411-7A, Harvard 
University, Radio Research Laboratory, Jan. 5, 1943. 

504. Progress Report of the Radio Research Laboratory, Report 

411-8, Harvard University, Radio Research Laboratory, 
Nov. 30, 1942. Div. 15-121-Ml 

505. Wide-Band Radar Warning Receivers, Zero-Catchers, 

Robert B. Barnes, Report 411-9, Project A-700, Har- 
vard University, Radio Research Laboratory, Jan. 21, 
1943. Div. 15-312. 1-Ml 

506. Progress Report of the Radio Research Laboratory, Report 

411-10, Harvard University, Radio Research Labora- 
tory, Dec. 31, 1942. Div. 15-121-Ml 

507. A Wide-Range Microwave Oscillator {A-1501), George E. 
Hulstede, Report 411-11, Harvard University, Radio 
Research Laboratory, Jan. 7, 1943. 

Div. 15-351. 1-Ml 

508. Progress Report of the Radio Research Laboratory, Report 

411-12, Harvard University, Radio Research Labora- 
tory, Jan. 30, 1943. Div. 15-121-Ml 

509. The RC-160 Receiver {Auto- Search) , E. L. Plotts, Report 
411-13, Project C-1100, Harvard University, Radio 
Research Laboratory, Mar. 1, 1943. 

Div. 15-311.3-Ml 

510. B502 Jamming Signal Generator, Roger J. Pierce, Report 

411-14, Harvard University, Radio Research Labora- 
tory, Dec. 28, 1942. Div. 15-512-Ml 

511. 100 Me Airborne Jamming Transmitter {B1700) {Navy 
CXCE), Louis E. Raburn, Report 411-15, Harvard 
University, Radio Research Laboratory, Mar. 13, 1943. 

Div. 15-322.16-M2 

512. Operating Instructions for Type D104-A Tuning Unit, 

David B. Sinclair, Report 411-16, Project D-lOO, Har- 
vard University, Radio Research Laboratory, Jan. 20, 
1943. Div. 15-311. 21-M2 

513. Operating Instructions for Type D102 Tuning Unit, 

David B. Sinclair, Report 411-17, Project D-lOO, Har- 
vard University, Radio Research Laboratory, Jan. 25, 
1943. Div. 15-311. 21-M3 

514. Wide-Band Cone Antennas {Preliminary Report), R. 
Silliman, Report 411-18, Harvard University, Radio 
Research Laboratory, Mar. 20, 1943. 

Div. 15-333.1-Ml 

515. Progress Report of the Radio Research Laboratory, Report 

411-19, Harvard University, Radio Research Labora- 
tory, Feb. 27, 1943. Div. 15-121-Ml 

516. The Vulnerability of Loran to Radio Countermeasures, A. 

Earl Cullum, Jr., and D. A. Peterson, Report 411-20, 
Project K-lOO, Harvard University, Radio Research 
Laboratory, Feb. 15, 1943. Div. 15-250-Ml 

517. Transformers and Chokes for Power Supplies, John P. 
Woods, Report 411-21, Harvard University, Radio Re- 
search Laboratory, Feb. 10, 1943. 

Div. 15-381. 1-Ml 

518. Preliminary Instructions B501 Pulse Signal Generator, 
Roger J. Pierce, Report 411-22, Harvard University, 
Radio Research Laboratory, Mar. 20, 1943. 

Div. 15-512-M2 


484 


BIBLIOGRAPHY 


519. Frequency Characteristics of Wide- Band Matching Sec- 

tions, Eugene Fubini, Peter J. Sutro, and R. F. Lewis, 
Report 411-23, Harvard University, Radio Research 
Laboratory, Apr. 19, 1943. Div. 15-381. 1-M2 

520. Preliminary Report on the Susceptibility to Jamming of 

the SCR-268, Oswald G. Villard, Jr., Report 411-24, 
Project E-200, Harvard University, Radio Research 
Laboratory, Feb. 27, 1943. Div. 15-221. 23-Ml 

521. Operating Instructions for D 1202- A Spectrum Analyzer, 
W. B. Caufield, Report 411-25, Harvard University, 
Radio Research Laboratory, Apr. 30, 1943. 

Div. 15-513-Ml 

522. Calculated Frequency Spectrum of RCA 931 Noise Source, 
R. D. Sard, Report 411-26, Harvard University, Radio 
Research Laboratory, Apr. 16, 1943. 

Div. 15-343. 1-M2 

523. Progress Report of the Radio Research Laboratory, Report 

411-27, Harvard University, Radio Research Labora- 
tory, Mar. 30, 1943. Div. 15-12 1-Ml 

524. Design Information for Several U.H.F. Filters, Seymour 
B. Cohn, Report 411-28, Harvard University, Radio 
Research Laboratory, Apr. 9, 1943. Div. 15-361-Ml 

525. The Spectra of Noise- Modulated Waves and Their Rela- 
tive Efficiencies for Barrage Jamming, David Middleton, 
Report 411-29, Project G-lOO, Harvard University, 
Radio Research Laboratory, Apr. 23, 1943. 

Div. 15-231-M2 

526. Operating Instructions for the C1700 Homing Device 

Attachment, Fanny, Paul H. Reedy, Report 411-30, 
Harvard University, Radio Research Laboratory, Mar. 
13, 1943. Div. 15-313.12-Ml 

527. B500 Synthetic Radar and Jamming Equipment for Lab- 
oratory Studies of Jamming, Roger J. Pierce, Report 
411-31, Project B-500, Harvard University, Radio Re- 
search Laboratory, Apr. 10, 1943. Div. 15-221. 1-M2 

528. Note on the Efficacy of a Series of Pulses for Barrage 

Jamming, John H. Van Vleck, Report 411-32, Project 
G-200, Harvard University, Radio Research Labora- 
tory, Apr. 16, 1943. Div. 15-231-Ml 

529. Progress Report of the Radio Research Laboratory, Report 

411-33, Harvard University, Radio Research Labora- 
tory, Apr. 30, 1943. Div. 15-121-Ml 

530. Measured Impedance Characteristics of Cylindrical Radi- 

ators Less than One Wavelength Long, C. Milton Daniell, 
Report 411-34, Harvard University, Radio Research 
Laboratory, Apr. 21, 1943. Div. 15-333. 1-M2 

531. The RRL Mandrel Transmitter {Army: RC-183), Charles 
W. Oliphant, Report 411-35, Harvard University, Radio 
Research Laboratory, May 21, 1943. 

Div. 15-322.14-Ml 

532. Preliminary Report on the Susceptibility to Jamming of 

the Navy A SVC or the Army SCR-521-A Radar, Oswald 
G. Villard, Jr., and S. F. Kaisel, Report 411-36, Project 
E-300, Harvard University, Radio Research Labora- 
tory, May 31, 1943. Div. 15-221. 21-Ml 

533. Network for Regulating A-C Voltage from Variable- Speed 
Generator, John P. Woods, Report 411-37, Harvard 
University, Radio Research Laboratory, May 7, 1943. 

Div. 15-391-Ml 

534. CW Oscillators Using the Experimental GE L-3 Triode in 
Coaxial Line Circuits, J. Gregg Stephenson, Report 


411-38, Harvard University, Radio Research Labora- 
tory, May 3, 1943. Div. 15-351. 2-Ml 

535. Techniques for Still and Cine-Photography of Cathode- 
Ray Tube Screen Patterns, E. R. Brill, C. Gray, A. M. 
Hughes, and O. G. Villard, Jr., Report 411-39, Harvard 
University, Radio Research Laboratory, May 6, 1943. 

Div. 15-344. 1-Ml 

536. The ANlAPQ-3 {A-2600) and ANjAPQ-d {A-2700) 

Wide-Range Microwave Superheterodyne Receivers, R. B. 
Holt, Report 411-40, Projects A-2600 and A-2700, Har- 
vard University, Radio Research Laboratory, June 2, 
1943. Div. 15-311. 127-Ml 

537. Jamming Studies of 10 CM Radar Systems, Ellis W. 
Shuler, Jr., J. J. Livingood, and J. H. Woodruff, H, 
Report 411-41, Project A- 1200, Harvard University, 
Radio Research Laboratory, July 9, 1943. 

Div. 15-221.2-Ml 

538. Report on the Susceptibility to Jamming of the Navy 
ASGjArmy SCR-617, J. H. Woodruff, H, Report 
411-42, Project L-400, Harvard University, Radio Re- 
search Laboratory, June 22, 1943. 

Div. 15-221.21-M2 

539. Progress Report of the Radio Research Laboratory, Report 

411-43, Harvard University, Radio Research Labora- 
tory, May 31, 1943. Div. 15-121-Ml 

540. Notes on Power Required for Noise Jamming, F. E. 
Terman and Warren D. White, Report 411-44, Harvard 
University, Radio Research Laboratory, June 18, 1943. 

Div. 15-221. 13-Ml 

541. The F-902, Carpet I, Airborne Jamming Transmitter 
{RRL prototype of Army RC-156, Navy CXCD), E. A. 
Yunker, Report 411-45, Harvard University, Radio 
Research Laboratory, July 20, 1943. 

Div. 15-322.124-Ml 

542. Results of the Field Jamming Tests and Laboratory Tests 

of the Replacement Video Amplifier for the SCR-717-B, 
J. H. Woodruff, H, Report 411-46, Project RP-277, 
Harvard University, Radio Research Laboratory, Aug. 
15, 1944. Div. 15-222.1-M8 

543. Progress Report of the Radio Research Laboratory, Report 

411-47, Harvard University, Radio Research Labora- 
tory, June 30, 1943. Div. 15-121-Ml 

544. Enemy Radar Characteristics, Howard A. Chinn, Report 

411-48, Harvard University, Radio Research Labora- 
tory, July 10, 1943. Div. 15-711. 1-Ml 

545. CW Oscillators Using the G. E. ZP-449 Triode in Coaxial 

Line Circuits, J. Gregg Stephenson and R. L. Henkel, 
Report 411-49, Harvard University, Radio Research 
Laboratory, July 12, 1943. Div. 15-351. 2-M2 

546. Recent Research on Window, F. L. Whipple and W. W. 
Farley, Report 411-50, Project G-500, Harvard Uni- 
versity, Radio Research Laboratory, July 1, 1943. 

Div. 15-241-M2 

547. The Spectrum of Clipped Noise, John H. Van Vleck, 

Report 411-51, Harvard University, Radio Research 
Laboratory, July 21, 1943. Div. 15-526-Ml 

548. Noise and Hum Reduction in Installations of RC-164 
Equipment in Large Airplanes, Seymour B. Cohn, 
Report 411-52, Project A-2100, Harvard University, 
Radio Research Laboratory, July 23, 1943. 

Div. 15-312. 1-M2 


BIBLIOGRAPHY 


485 


549. Preliminary Report on the Susceptibility to Jamming of 
the Navy Mark IV {FD) Radar, D. R. Scheuch and S. F. 
Kaisel, Report 411-53, Project E-500, Harvard Univer- 
sity, Radio Research Laboratory, Sept. 9, 1943. 

Div. 15-221. 22-Ml 

550. Progress Report of the Radio Research Laboratory, Report 

411-54, Harvard University, Radio Research Labora- 
tory, Aug. 4, 1943. Div. 15-121-Ml 

551. Jamming of the Type A Presentation with Sine Wave A M, 
Noise AM, and with Dina, Donald W. Taylor and D. A. 
Peterson, Report 411-55, Project K-400, Harvard Uni- 
versity, Radio Research Laboratory, Sept. 23, 1943. 

Div. 15-221.32-Ml 

552. Four Types of Frequency Modulation and Their Possible 

Use for Radar and Communication Jamming, David 
Middleton and M. Steinberg, Report 411-56, Project 
G-300, Harvard University, Radio Research Labora- 
tory, Sept. 23, 1943. Div. 15-231-M3 

553. Operating Characteristics of the 931 Phototube in the 
Frequency Range 50 to 5000 Kc, J. D. Cobine and C. J. 
Gallagher, Report 411-57, Harvard University, Radio 
Research Laboratory, Aug. 31, 1943. 

Div. 15-343. 1-M3 

554. Progress Report of the Radio Research Laboratory, Report 

411-58, Harvard University, Radio Research Labora- 
tory, Sept. 8, 1943. Div. 15-121. Ml 

555. Considerations Concerning Radar Chicks, Eugene Fubini 
and T. S. Kuhn, Report 411-59, Harvard University, 
Radio Research Laboratory, Sept. 17, 1943. 

Div. 14-412-M4 

556. Internal Progress Report of the Radio Research Labora- 
tory, Report 411-60, Harvard University, Radio Re- 
search Laboratory, Oct. 5, 1943. 

Div. 15-121-Ml 

557. Field Tests of Dina and Dinamate at Wright Field, 
August 15, 1943, Harvey Kees and Louis Raburn, 
Report 411-61, Harvard University, Radio Research 
Laboratory, Sept. 21, 1943. 

Div. 15-321. 11-M2 

558. F-2500 Higher Power Carpet Transmitter {Carpet III) 

{RRL prototype of AN /APQ-9), James L. Clark, Report 
411-62, Harvard University, Radio Research Labora- 
tory, Sept. 30, 1943. Div. 15-322. 121-M3 

559. Document Digest of the Radio Research Laboratory, A. H. 
Halloran, Report 411-64, Harvard University, Radio 
Research Laboratory, Sept. 1, 1944. 

Div. 15-122-Ml 

560. Supplement to Document Digest, A. H. Halloran, Report 

411-64A, Harvard University, Radio Research Labora- 
tory, Oct. 15, 1944. Div. 15-122-Ml 

561. Document Digest, A. H. Halloran, Report 411-64B, 

Harvard University, Radio Research Laboratory, June 
1, 1945. Div. 15-122-Ml 

562. Document Digest, A. H. Halloran, Report 411-64C, 
Harvard University, Radio Research Laboratory. 

563. Jamming of the Type A Presentation with Sine Wave FM, 
Noise FM, and with Various Combinations of FM and 
AM, Donald W. Taylor and D. A. Peterson, Report 
411-65, Project RP-186, Harvard University, Radio 
Research Laboratory, Nov. 26, 1943. 

Div. 15-221.32-M2 


564. Jamming Tests against the Orlando Air Defense System, 

August 4-9, 1943, H. C. Pollock, Report 411-66, Project 
RP-246, Harvard University, Radio Research Labora- 
tory, Sept. 22, 1943. Div. 15-722-M2 

565. Summarized Report of Beaver I Mission, Charles W. 
Oliphant, Report 411-67, Harvard University, Radio 
Research Laboratory, Dec. 28, 1943. 

Div. 15-712-Ml 

566. Noise in Gas Tubes, J. D. Cobine and C. J. Gallagher, 
Report 411-68, Project RP-186, Harvard University, 
Radio Research Laboratory, Jan. 24, 1944. 

Div. 15-343.2-Ml 

567. Preliminary Test Results on Westinghouse 10 kw Mag- 

netron, Gunnar Hok, Report 411-70, Project RP-321, 
Harvard University, Radio Research Laboratory, Aug. 
18, 1944. Div. 15-341. 5-M2 

568. Transmitter and Antenna for 10-kw Magnetron, Gunnar 
Hok and M. E. Gottlieb, Report 411-70A, Project 
RP-321 and SC-94.19, Harvard University, Radio Re- 
search Laboratory, Jan. 11, 1946. 

Div. 15-341. 5-M5 

569. The Effectiveness of AM, FM, and Dina Jamming of the 
Type A Presentation as a Function of I-F and of Video 
Overloading, Donald W. Taylor, Report 411-71, Project 
RP-186, Harvard University, Radio Research Labora- 
tory, Jan. 12, 1944. 

Div. 15-221. 32-M3 

570. A Preliminary Report on the Susceptibility to Jamming of 

the SCR-717-B, J. H. Woodruff, H, Report 411-72, 
Project RP-277, Harvard University, Radio Research 
Laboratory, Dec. 15, 1943. Div. 15-221. 21-M3 

571. A Study of Chaff Echoes at 515 Me, Gerard P. Kuiper, 
Report 411-73, Project RP-257, Harvard University, 
Radio Research Laboratory, Dec.' 19, 1943. 

Div. 15-241. 1-Ml 

572. Magnets for the 6D4 Noise Tube, J. D. Cobine, Report 
411-74, Project RP-187, Harvard University, Radio 
Research Laboratory, Aug. 31, 1944. 

Div. 15-343.241-M6 

573. Jamming of the Type A Presentation with Periodic Pulses 
and with Random Pulses, Donald W. Taylor and James 
M. Moran, Report 411-75, Project RP-186, Harvard 
University, Radio Research Laboratory, Jan. 25, 1944. 

Div. 15-221.32-M4 

574. Audio and Supersonic Noise Generators, J. D. Cobine, 
Report 411-76, Project RP-187, Harvard University, 
Radio Research Laboratory, Aug. 31, 1944. 

Div. 15-343.241-M7 

575. The Theoretical Effect of Integration on the Visibility of 
Weak Signals through Noise, Peter J. Sutro, Report 
411-77, Project RP-318, Harvard University, Radio 
Research Laboratory, Feb. 4, 1944. 

Div. 15-221. 12-M3 

576. Principles for the Design of Small Power Transformers, 

John P. Woods, Report 411-78, Project RP-178, Har- 
vard University, Radio Research Laboratory, Jan. 25, 
1944. Div. 15-381. 1-M4 

577. Wide Band Waveguide Mixers, Ralph H. Hoglund, A. J. 

Yakutis, and J. S. Foster, Jr., Report 411-79, Project 
RP-286, Harvard University, Radio Research Labora- 
tory, Oct. 16, 1944. Div. 15-371. 1-M2 


486 


BIBLIOGRAPHY 


578. Jamming of the Type B Presentation, Donald VV. Taylor 

and J. M. Moran, Report 411-80, Project RP-186, 
Harvard University, Radio Research Laboratory, Feb. 
21, 1944. Div. 15-221.33-Ml 

579. Synthetic Giant Wurzburg, F. P. Cowan, Report 411-81. 

Project RP-179, Harvard LTniversity, Radio Research 
Laboratory, Mar. 15, 1944. Div. 15-221. 4-Ml 

580. Synthetic Giant Wurzburg {Antenna Modification) , J. F. 
Youngblood, Report 411-81A, Project RP-179, Harvard 
University, Radio Research Laboratory, June 22, 1944, 

Div. 15-221.4-M2 

581. Class C Operation of Reactance Tubes, W. R. Rambo, 
Report 411-82, Project RP-203, Harvard University, 
Radio Research Laboratory, Feb. 4, 1944. 

Div. 15-345-M2 

582. The G. E. ZP-522 Triode as a CW Oscillator and Ampli- 
fier in Coaxial Line Circuits, J. Gregg Stephenson and 
R. L. Henkel, Report 411-83, Project RP-204, Harvard 
University, Radio Research Laboratory, Mar. 15, 1944. 

Div. 15-351. 2-M4 

583. The Improvement in Minimum Detectable Signal in Noise 
through the Use of the Long Afterglow CR Tube and 
through Photographic Integration, E. R. Brill, Report 
411-84, Project RP-318, Harvard University, Radio 
Research Laboratory, Feb. 8, 1944. 

Div. 15-222. 1-M3 

584. The Effectiveness of Jamming of the Type B Presentation 
as a Function of I- F and of Video Overloading, Donald W. 
Taylor, Report 411-85, Project RP-186, Harvard Uni- 
versity, Radio Research Laboratory, Mar. 27, 1944. 

Div. 15-221.33-M2 

585. Theory of the Visual vs Aural or Meter Reception of Radar 
Signals in the Presence of Noise, John H. Van Vleck, 
Report 411-86, Project RP-181, Harvard University, 
Radio Research Laboratory, May 5, 1944. 

Div. 15-221.12-M5 

586. Note on the Theory of Square-Law Rectification of a 
Modulated Carrier in the Presence of Noise, David Mid- 
dleton, Report 411-86A, Project RP-181, Harvard 
University, Radio Research Laboratory, July 12, 1944. 

Div. 15-221. 12-M6 

587. On the Use of a High Power Ground Jammer against the 
German A1 Radar, W. G. Dow and J. Galt, Report 
411-88, Project RP-lOO, Harvard University, Radio 
Research Laboratory, Mar. 22, 1944. 

Div. 15-402.1-Ml 

588. Constant Field Strength Grotind Plane for Receiver R.F. 

Response Measurements, Seymour B. Cohn, Report 
411-89, Harvard University, Radio Research Labora- 
tory, Apr. 3, 1944. Div. 15-527-Ml 

589. A Calculation of the Effect of Rectification and Clipping 
on the Spectra of the Output of the 6D4, 884, 178 A, and 
2D21 Noise Sources, David Middleton, Report 411-90, 
Project RP-181, Harvard University, Radio Research 
Laboratory, June 23, 1944. 

Div. 15-343.243-M2 

590. Review of Window, Gerard P. Kuiper, Report 411-91, 

Project RP-103, Harvard University, Radio Research 
Laboratory, May 30, 1944. Div. 15-241-M5 

591. Noise Output of the Sylvania 6D4 Gas Triode at Audio 
and Supersonic Frequencies, J. D. Cobine, Report 


411-92, Project RP-187, Harvard University, Radio 
Research Laboratory, May 29, 1944. 

Div. 15-343.241-M4 

592. Theory of Ship Echoes as Applied to Naval RCM Opera- 

tions, T. S. Kuhn, Report 411-93, Project RP-186, 
Harvard University, Radio Research Laboratory, July 
14, 1944. Div. 15-221. 11-M2 

593. Report of AJ J Traming Committee, F. P. Cowan, Report 
411-94, Project RP-387, Harvard University, Radio 
Research Laboratory, June 5, 1944. 

Div. 15-650-Ml 

594. Survey of German Radar from the Countermeasures Pomt 
of View, R. D. Sard, Report 411-95, Harvard Univer- 
sity, Radio Research Laboratory, Sept. 4, 1944. 

Div. 15-71 1.1-M2 

595. Video Spectrum Analyzer, G. P. McCouch and P. S. 
Jastram, Report 411-96, Project RP-176, Harvard Uni- 
versity, Radio Research Laboratory, July 10, 1944. 

Div. 15-513-M4 

596. A Theoretical Study of the Response of Saturated Linear 
and Quadratic Rectifiers to Random Noise. Calcidations 
for the 6D4 Noise Source, David Middleton, Report 
411-97, Project RP-181, Harvard University, Radio 
Research Laboratory, Oct. 23, 1944. 

Div. 15-343.241-M8 

597. Report on A SG Field Testing Program, J. H. Woodruff, 1 1 , 
and A. Keck, Report 411-98, Project RP-172, Harvard 
University, Radio Research Laboratory, July 27, 1944. 

Div. 15-722-M4 

598. Theory of Reduction of Submarine Echoes by Shielding 

Screens, Robert Weinstock, Report 411-99, Project 
R P-406, Harvard LTniversity, Radio Research Labora- 
tory, Oct. 3, 1944. Div. 15-242-Ml 

599. Antennas for RCM, Andrew Alford, Report 411-100, 

Harvard University, Radio Research Laboratory, Nov. 
1, 1944. Div. 15-330-Ml 

600. High-Gain Antefina for S-Band Transmitter, Clare Dris- 
coll, Report 411-101, Project RP-303, Harvard Univer- 
sity, Radio Research Laboratory, Sept. 18, 1944. 

Div. 15-332. 2 7-Ml 

601. Wide Band UHF A mplifier {D1410), John P. Woods and 
R. O. Petrich, Report 411-102, Project RP-210, Harvard 
University, Radio Research Laboratory, Sept. 22, 1944. 

Div. 15-243-Ml 

602. Theory of the Radar Response of Chaff, John H. Van 
Vleck, Felix Bloch, and Morton Hamermesh, Report 
411-103, Project RP-406, Harvard University, Radio Re- 
search Laboratory, Oct. 13, 1944. Div. 1 5-241. 1-M5 

603. Tests of M-4100 System Installed on U. S. S. Gunason, 

Andrew Alford, W. D. McGuigan, J. Margolin, and 
P. L. Harbury, Report 411-105, Project RP-271, Har- 
vard University, Radio Research Laboratory, Sept. 25, 
1944. Div. 15-313.22-Ml 

604. A Condensed Summary of the Present Status of Window 

Development at RRL, F. L. Whipple, Report 411-106, 
Project RP-103, Harvard University, Radio Research 
Laboratory, Oct. 2, 1944. Div. 15-241-M6 

605. Preliminary Experimental Results with the Z-3600 Re- 

peater, Louis E. Raburn and Harvey Kees, Report 
411-107, Harvard University, Radio Research Labora- 
tory, Oct. 11, 1944. Div. 15-315-Ml 


BIBLIOGRAPHY 


487 


606. Broad-Band Tests of AN / APT-4 {XA-2) Transmitter in 
the Wurzburg Radar Band, Warren D. White, Report 
411-108, Project RP-338, Harvard University, Radio 
Research Laboratory, Oct. 11, 1944. 

Div. 15-322.15-M2 

607. Shiphorne Tests of M2600 {CXGA) Radar and Radio 
Direction Finder, J. D. Kraus, H. K. Clark, and A. N. 
Morgan, Report 411-109, Project RP-271, Harvard 
University, Radio Research Laboratory, Oct. 11, 1944. 

Div. 15-313.21-Ml 

608. Modification of SCR-648 to Simulate German Wurzhurgs, 
D. R. Scheuch, F. P. Cowan, and M. L. Towle, Report 
411-110, Project RP-343, Harvard University, Radio 
Research Laboratory, Oct. 11, 1944. 

Div. 15-221.4-M3 

609. Raven Installations and Tests on Navy PB4Y-2 Recon- 
naissance Aircraft {Albatross 1), R. L. Hammett, Report 
411-111, Project RP-242, Harvard University, Radio 
Research Laboratory, Sept. 20, 1944. 

Div. 15-401. 5-Ml 

610. The Use of Lobe- Switching in Transmission Only, as an 
A/ J Measure, E. R. Brill and F. P. Cowan, Report 411- 
112, Project RP-318, Harvard LTniversity, Radio Re- 
search Laboratory, Oct. 20, 1944. Div. 1 5-222. 1-M9 

611. The M4601 and M4602 High-Pass Filters, Peter L. 
Harbury, Report 411-113, Project RP-286, Harvard 
University, Radio Research Laboratory, Nov. 5, 1944. 

Div. 15-361. 2-Ml 

612. Preliminary Report of M6300 Antemias, E. L. Bock and 
J. A. Nelson, Report 411-114, Project RP-138, Harvard 
University, Radio Research Laboratory, Oct. 23, 1944. 

Div. 15-331.32-M2 

613. Resonant Section Coaxial Filters, Paul 1. Richards, 
Report 411-115, Project RP-286, Harvard University, 
Radio Research Laboratory, Oct. 18, 1944. 

Div. 15-361-M2 

614. An Easily Constructed High-Pass Coaxial Filter, Paul 1. 
Richards, Report 411-115A, Project RP-442, Harvard 
University, Radio Research Laboratory, Mar. 9, 1945. 

Div. 15-361. 2-M2 

615. Spurious Responses in a Transmission-Line Low- Pass 

Filter, Paul 1. Richards, Report 411-115B, Project 
RP-442, Harvard University, Radio Research Labora- 
tory, Mar. 15, 1945. Div. 15-361. 1-M2 

616. A Note on UHF Coupled Circuits, Paul 1. Richards, 
Report 411-115C, Project RP-442, Harvard University, 
Radio Research Laboratory, Mar. 20, 1945. 

Div. 15-383-M6 

617. Supplementary Information on Resonant-Section, Coaxial 
Filters, Paul 1. Richards, Report 411-115D, Projects 
RP-442, AC-290.12, and AC-290.16, Harvard Univer- 
sity, Radio Research Laboratory, July 16, 1945. 

Div. 15-361. M3 

618. A Triode Oscillator — Tripler, W. R. Rambo and L. D. 
Tuck, Report 411-116, Project RP-169, Harvard Uni- 
versity, Radio Research Laboratory, Oct. 20, 1944. 

Div. 15-351.2-M6 

619. Carpet Transmitter Modification, Elton Barrett, Report 
411-117, Project RP-165, Harvard University, Radio 
Research Laboratory, Oct. 17, 1944. 

Div. 15-322.124-M6 


620. A/J Wiring Changes in SCR-268, Richard S. O’Brien 

and W. Y. Pan, Report 411-118, Project RP-171, Har- 
vard University, Radio Research Laboratory, Oct. 26, 
1944. Div. 15-221. 23-M2 

621. Semi-Empirical Relations between the Gain, Aperture, 
Beam Width and Shape of High-Gain Antennas, Andrew 
Alford and 1. G. Clarke, Report 411-119, Harvard Uni- 
versity, Radio Research Laboratory, Oct. 19, 1944. 

Div. 15-333.54-M2 

622. M6302 Skirted-Stub Antenna, J. A. Nelson, Report 
411-120, Projects RP-138 and NA-178, Harvard Uni- 
versity, Radio Research Laboratory, Sept. 28, 1945. 

Div. 15-332.121-Ml 

623. 1-Kw Water Load for the Measurement of R-F Power, 

W. R. Rambo and S. W. Howe, Report 411-121, Project 
RP-306, Harvard University, Radio Research Labora- 
tory, Nov. 3, 1944. Div. 15-52 1-Ml 

624. Spot Frequency Jamming Techniques, F. P. Cowan, 

Report 411-122, Harvard University, Radio Research 
Laboratory, Nov. 6, 1944. Div. 15-232-M4 

625. Attenuation of RG-21f A U Cable as a Function of Fre- 
quency, Walter G. Wadey and Thomas E. Moore, Report 
411-123, Project RP-107, Harvard University, Radio 
Research Laboratory, Nov. 13, 1944. 

Div. 15-371.3-Ml 

626. Peak-Reading Voltmeter, P. S. Jastram, Report 411-124, 

Project RP-187, Harvard University, Radio Research 
Laboratory, Apr. 5, 1945. Div. 15-516-Ml 

627. Estimate of Square Sheet Echo Cross-Section: Theoretical 
Evaluation of Broadside Echoes from Circular Cylinder for 
Perpendicular Polarization, Robert Weinstock, Report 
411-125, Project RP-406, Harvard University, Radio 
Research Laboratory, Nov. 14, 1944. 

Div. 15-241. 1-M6 

628. Test Information on Resnatron Type X-124 and X-139, 
W. R. Rambo, L. D. Tuck, and S. W. Howe, Report 
411-126, Project RP-378, Harvard University, Radio Re- 
search Laboratory, Nov. 16, 1944. Div. 15-342-M3 

629. Power Output Indicators, E. A. Yunker, Report 411-127, 

Project RP-290, Harvard University, Radio Research 
Laboratory, Nov. 17, 1944. Div. 15-521. 2-M2 

630. ’’ Analysis for a Possible A/J System against Window, 

David Middleton and Peter J. Sutro, Report 411-128, 
Project RP-182, Harvard University, Radio Research 
Laboratory, Dec. 9, 1944. Div. 15-222. 2-M2 

631. Identification of Naval Spoofs, Lewis R. Roller, Report 
411-129, Project RP-258, Harvard University, Radio 
Research Laboratory, Nov. 29, 1944. 

Div. 15-222.2-Ml 

632. Noise Modulation of the ZP 612-6-3 Magnetron at Power 

Levels near 300 Watts, F. H. Crawford, Report 411-130, 
Project RP-417, Harvard University, Radio Research 
Laboratory, Dec. 6, 1944. Div. 15-341. 3-Ml 

633. A/J Study of Navy RHB, F. P. Cowan, Ralph H. 

Hoglund, and D. R. Scheuch, Report 411-131, Project 
RP-355, Harvard University, Radio Research Labora- 
tory, Nov. 17, 1944. Div. 15-263-M2 

634. APR-2 Receiver Modifications, Paul A. Pearson, Report 
411-132, Project RP-139, Harvard University, Radio 
Research Laboratory, Nov. 30, 1944. 

Div. 15-311. 122-Ml 


488 


BIBLIOGRAPHY 


635. Study of Power Requirements for S-Band Jamming from 

Surface Vessels, Warren D. White, Report 411-133, 
Project RP-169, Harvard University, Radio Research 
Laboratory, Dec. 13, 1944. Div. 15-403. 3-Ml 

636. Tabulation of Antenna Spinner Assemblies for Group M 

Direction- Finding System, J. D. Kraus, Report 411-134, 
Harvard University, Radio Research Laboratory, Dec. 
4, 1944. Div. 15-331. 2-M2 

637. Comparison of APQ-2 and APT-1 plus AM- 18 for 

Jamming Effectiveness at 206 Me, D. A. Peterson, Report 
411-135, originally issued as Test Report 411-TR-46, 
Harvard University, Radio Research Laboratory, Nov. 
27, 1944. Div. 15-404-Ml 

638. Comparison of APQ-2 and APT-1 plus AM-18 / APT for 
Jamming Effectiveness at 210 Me, J. F. Youngblood and 
R. E. Anderson, Report 411-135A, Harvard University, 
Radio Research Laboratory, Feb. 12, 1945. 

Div. 15-404-M2 

639. Audio and Supersonic Noise Characteristics of the RCA 
884 and 2050 Gas Tubes, 25 cps to 100 kc, J. D. Cobine, 

C. J. Gallagher, and P. S. Jastram, Report 411-136, 

Project RP-187, Harvard University, Radio Research 
Laboratory, Dec. 12, 1944. Div. 15-343. 242-M6 

640. Resonant Probe in Waveguide, Thomas E. Moore and 

Walter G. Wadey, Report 411-137, Project RP-107, 
Harvard University, Radio Research Laboratory, Dec. 
26, 1944. Div. 15-371. 1-M3 

641. Sensitivity of the AN /APR-5 A in Waveguide, 3 to 10 CM, 
Thomas E. Moore and Walter G. Wadey, Report 411- 
138, Project RP-107, Harvard University, Radio Re- 
search Laboratory, Dec. 26, 1944. 

Div. 15-371. 1-M4 

642. Single-Dial Operation of AN/ APT-4 {XA-2), F3400 
Magnetron Transmitter, Louis E. Raburn and G. R. 
Bridgeford, Report 411-139, Project RP-338, Harvard 
University, Radio Research Laboratory, Dec. 19, 1944. 

Div. 15-322.15-M3 

643. Analysis of the Effectiveness of Countermeasures, Felix 

Bloch and Morton Hamermesh, Report 411-140, Project 
RP-103, Harvard University, Radio Research Labora- 
tory, Dec. 20, 1944. Div. 15-710-Ml 

644. Modification of ASC-1 for Dual-Polarization Operation, 

D. R. Scheuch, Report 411-141, Project RP-406, Har- 

vard University, Radio Research Laboratory, Dec. 21, 
1944. Div. 15-221.4-M4 

645. A Modification to the F-3500 {AN /APT-5, AN/SPT-6) 

Transmitter to Improve the Power Output in the 350 to 
700 Me Range, H. C. Kriegel, Report 411-142, Project 
RP-336, Harvard University, Radio Research Labora- 
tory, Dec. 26, 1944. Div. 15-322. 123-M2 

646. Blanking of the AN / APR-5 Search Receiver, W. H. 

Huggins and J. J. Wedel, Report 411-143, Project RP- 
286, Harvard University, Radio Research Laboratory, 
Dec. 30, 1944. Div. 15-31 1.1 24-M2 

647. The Pulse-Stretcher as a Device for Increasing the Audio 
Sensitivity of Search Receivers, W. H. Huggins and J. W. 
Kearney, Report 411-144, Project RP-286, Harvard 
University, Radio Research Laboratory, Mar. 14, 1945, 

Div. 15-311.22-Mi 

648. A/J Study of Mark 31 Receiver {Bat), F. P. Cowan, 
Ralph H. Hoglund, and D. R. Scheuch, Report 411-146, 


Project RP-436, Harvard University, Radio Research 
Laboratory, Dec. 30, 1944. Div. 15-263-M4 

649. Moisture in Waveguides, Thomas E. Moore and Walter 
G. Wadey, Report 411-147, Project RP-107, Harvard 
University, Radio Research Laboratory, Jan. 6, 1945. 

Div. 15-371. 1-M5 

650. Conversion of AN/ APR-1 for Reduced Bandwidth and 

Sensitivity, Matthew T. Lebenbaum, Report 411-148, 
Project RP-144, Harvard University, Radio Research 
Laboratory, Jan. 10, 1945. Div. 15-31 1.121-M2 

651. Waveguide Installation for AN /APR-5A, Thomas E. 

Moore and Walter G. Wadey, Report 411-149, Project 
RP-107, Harvard University, Radio Research Labora- 
tory, Jan. 8, 1945. Div. 15-371. 1-M6 

652. Single-Dial Operation of Carpet 1 {AN/ APT-2), Elton 

Barrett and A. Ellis, Report 411-150, Project RP-165, 
Harvard University, Radio Research Laboratory, Jan. 
12, 1945. Div. 15-322.122-Ml 

653. The Barrage Suitability of Carpet I and III with or 

without Window, J. J. Youngblood, Report 411-151, 
Harvard LTniversity, Radio Research Laboratory, Jan. 
25, 1945. Div. 15-322. 124-M7 

654. Minimum Detectable Signal as a Function of Frequency 

and Other Characteristics of AN / APR-5 A, Thomas E. 
Moore and Walter G. Wadey, Report 411-152, Project 
RP-107, Harvard University, Radio Research Labora- 
tory, Mar. 5, 1945. Div. 15-31 1.124-M3 

655. The A T-52/APT, A T-53/APTandA T-54/APT {M313) 

Stub Antenna Masts, and Assemblies Which Include 
Them, Peter L. Harbury, Report 411-153, Project RP- 
138, Harvard University, Radio Research Laboratory, 
Jan. 29, 1945. Div. 15-331.1 11-M3 

656. Low-Frequency Spectrum Analyzer, P. S. Jastram, Report 

411-154, Project RP-306, Harvard University, Radio 
Research Laboratory, Jan. 24, 1945. Div. 15-513-M8 

657. Proof-of-Performance Measurements of Tuba {A-500C), 

D. A. Peterson, Report 411-155, Project RP-lOO, Har- 
vard University, Radio Research Laboratory, Feb. 2, 
1945. Div. 15-402. 1-M2 

658. Flight Tests of an AN / APA-24 Antenna with Electric 

Drive, O. W. Whitby, Report 411-156, Project RP-284, 
Harvard University, Radio Research Laboratory, Feb. 
5, 1945. Div. 15-332-M2 

659. Analysis and Application of Measurements of Radar 
Cross-Section of Airplane Models, Morton Hamermesh, 
Report 411-157, Project RP-299, Harvard University, 
Radio Research Laboratory, Feb. 12, 1945. 

Div. 15-822.1-Ml 

660. Analysis and Application of Measurements of Radar 

Cross-Section of Airplane Models — II, A. T. Goble, 
Morton Hamermesh, and Eleanor Pressly, Report 411- 
157A, Projects RP-299, AC-294.22, and SC-94.22, Har- 
vard LTniversity, Radio Research Laboratory, Sept. 14, 
1945. Div. 15-822. 1-M2 

661. The Use of Continuously Rotating Direction Finders 
against Signals of Varying Intensity, Donald Foster, Re- 
port 411-158, Project RP-318, Harvard University, Radio 
Research Laboratory, Feb. 17, 1945. Div. 15-313-Ml 

662. Applications of Butterfly Circuits, R. A. Soderman, Re- 
port 41 1-159, Project RP-416, Harvard University, Radio 
Research Laboratory, Feb. 21, 1945. Div. 15-383-M5 


BIBLIOGRAPHY 


489 


663. Analysis of U.H.F. Resonant Systems by External 
Impedance Measurements, Gunnar Hok, Report 411-160, 

Project RP-321, Harvard University, Radio Research 
Laboratory, Feb. 28, 1945. Div. 15-522-Ml 

664. A Variable Cut-Off High-Pass Filter for Use with 
AN /APR-5 A, Walter G. Wadey, Report 411-161, 

Project RP-107, Harvard University, Radio Research 
Laboratory, Mar. 14, 1945. Div. 15-361. 2-M3 

665. Range Extender for General Radio 7 60 A Sound Analyzer, 

J. D. Cobine and J. R. Curry, Report 411-162, Project 
RP-187, Harvard University, Radio Research Labora- 
tory, Mar. 10, 1945. Div. 15-515-M3 

666. Design of Microwave Low-Pass Filters, Seymour B. Cohn, 

Report 411-163, Projects RP-442 and SC-90.12, Har- 
vard University, Radio Research Laboratory, June 1, 

1945. Div. 15-361. 1-M3 

667. I-F Circuit Modifications of SCR-268, W. Y. Pan, Re- 
port 411-164, Project RP-171, Harvard University, 

Radio Research Laboratory, Mar. 23, 1945. 

Div. 15-222.1-M12 

668. Radio Research Laboratory Film List March 20, 1945, 

S. W. Athey, Report 411-165, Harvard University, 

Radio Research Laboratory, Mar. 22, 1945. 

Div. 15-123-Ml 

669. Preliminary Report on the M6804 Antennas, David 
Lazarus, Report 411-166, Project RP-303, Harvard 
University, Radio Research Laboratory, Mar. 26, 1945. 

Div. 15-331. 16-Ml 

670. An A/ J Measure for Setting on Receivers, J. H. Wood- 
ruff, 1 1, Report 411-167, Project RP-447, Harvard 
University, Radio Research Laboratory, Mar. 26, 1945. 

Div. 15-232-M5 

671. C1900 VHF Homing Methods and Homing Equipment, 

John W. Christensen, Report 411-168, Projects RP-209 
and NS-312, Harvard University, Radio Research 
Laboratory, Apr. 10, 1945. Div. 15-313. 13-Ml 

672. The Characteristics of the Sylvania 6D4 Miniature Gas 
Triode as a Noise Source for the Range 0.1-5 Me, J. D. 

Cobine and J. R. Curry, Report 411-169, Project RP- 
187, Harvard University, Radio Research Laboratory, 

Mar. 30, 1945. Div. 15-343.241-MlO 

673. The RRL E2106 Aural Doppler Attachment for the Mark 
4 Radar, H. O. Anger, Report 411-170, Project RP-406, 
Harvard University, Radio Research Laboratory, Apr. 

9, 1945. Div. 15-221. 11-M3 

674. Probability Formulas for Simultaneous Periodically Re- 
curring Events, Paul 1. Richards, Report 411-171, 

Project RP-286, Harvard University, Radio Research 
Laboratory, May 5, 1945. Div. 15-31 1.5-Ml 

675. Class B Video Amplifiers for Power Amplification of 

Noise Energy, John F. Byrne, Report 411-172, Project 
R P-405 A, Harvard University, Radio Research Labora- 
tory, Apr. 11, 1945. Div. 15-382-Ml 

676. Flight Tests of AN / APA-23 Recorder, R. E. Anderson, 

Report 411-173, Project RP-276, Harvard University, 

Radio Research Laboratory, Apr. 12, 1945. 

Div. 15-311. 31-M4 

677. Probability Calculations on Chaff Clouds, Protecting 
against MC 382 Fuzes, Felix Bloch, Report 411-174, 

Project RP-406, Harvard University, Radio Research 691. 
Laboratory, Apr. 20, 1945. Div. 15-241. 1-M7 


678. Space- Charge-Limited Single-Stream Solutions in a Cy- 
lindrical Magnetron with Small Current, Felix Bloch, 
Report 411-175, Project RP-295, Harvard University, 
Radio Research Laboratory, May 25, 1945. 

/ Div. 15-341. 6-M6 

679. Probe Voltmeters, J. G. C. Swinney, Jr., Report 411-177, 

Harvard University, Radio Research Laboratory, May 
5, 1945. Div. 15-516-M2 

680. Summary of A/ J Developments for A SB Radar Systems, 

R. E. Kell, Report 411-178, Projects RP-223 and NA- 
159, Harvard University, Radio Research Laboratory, 
Apr. 15, 1945. Div. 15-221. 22-M2 

681. Summary of A/J Developments for the SCR-268 Radar 
System, W. Y. Pan and Richard S. O’Brien, Report 
411-179, Projects RP-171 and SC-92.07, Harvard Uni- 
versity, Radio Research Laboratory, May 2, 1945. 

Div. 15-221. 23-M3 

682. Operational Use of the AN / APA-24 D/F Antenna on 
B-29 Aircraft of the XX Bomber Command, John J. 
Wittkopf, Report 411-180, Harvard University, Radio 
Research Laboratory, Apr. 28, 1945. 

Div. 15-331. 12-M2 

683. Mark I of M4130 Modification of AN/ SPT-6 Radar Set 

for Use as Variable- Frequency Radar Transmitter, E. C. 
Barkofsky, Report 411-181, Projects RP-271, NS-202, 
and NS-261, Harvard University, Radio Research 
Laboratory, Apr. 30, 1945. Div. 15-313. 22-M2 

684. A Report on the Susceptibility of the SCR-720A to Jam- 
ming, J. H. Woodruff, H, Report 411-183, Projects 
RP-367 and SCR-720A, Harvard University, Radio Re- 
search Laboratory, Apr. 26, 1945. 

Div. 15-221. 21-M4 

685. Recent Progress in the Study of Tunable Squirrel- Cage 

Magnetrons, F. H. Crawford, Report 411-184, Project 
RP-295, Harvard University, Radio Research Labora- 
tory, May 10, 1945. Div. 15-341. 1-Ml 

686. Magnetron Modulation by Means of a Rotating Electron 
Cloud, F. Crawford and M. Pease, Report 411-185, 
Projects RP-417, vSC-94.25, and NS-278, Harvard Uni- 
versity, Radio Research Laboratory, Nov. 15, 1944. 

Div. 15-341.6-Ml 

687. Design of Simple Broad-Band Wave guide-to- Coax Junc- 
tions, Seymour B. Cohn, Report 411-186, Projects 
RP-442b, AC-290.16, and AC-290.12, Harvard Uni- 
versity, Radio Research Laboratory, July 18, 1945. 

Div. 15-371. 1-M7 

688. Flight Test of APQ-20 in B-17, James M. Moran, Report 

411-187, Projects RP-454, AC-294.20, and NA-189, 
Harvard University, Radio Research Laboratory, May 
23, 1945. Div. 15-401. 3-Ml 

689. Preliminary Flight Tests of APQ-20 in B-29, James M. 

Moran, Report 411-187A, Projects RP-454 and AC- 
294.20, Harvard University, Radio Research Labora- 
tory, June 9, 1945. Div. 15-401. 3-M2 

690. Flying Dutchman — Modification of Search Radar to 

Provide Target-Complexity Indication, E. R. Brill and 
Ralph H. Hoglund, Report 411-188, Projects RP-406J 
and NA-180, Harvard University, Radio Research 
Laboratory, May 21, 1945. Div. 15-221. 12-M7 

Calibration Methods for DEM-1 Radio and Radar Direc- 
tion Finder, W. D. McGuigan, E. C. Barkofsky, and 


490 


BIBLIOGRAPHY 


J. D. Kraus, Report 411-190, Projects RP-271, NS-202, 
and NS-261, Harvard University, Radio Research Lab- 
oratory, July 18, 1945. Div. 15-313.22-M3 

692. Interpretation of Calibration Data on Shipborne DBM 
(M4100) Radio and Radar Direction Finder, J. D. Kraus 
and W. D. McGuigan, Report 411-191, Projects RP-271, 
NS-202, and NS-261, Harvard University, Radio Re- 
search Laboratory, Dec. 8, 1945. Div. 15-313. 22-M4 

693. Optimum Directivity Pattern for Search Antennas, Donald 

Foster, Report 411-192, Projects RP-107 and SC-90.14, 
Harvard University, Radio Research Laboratory, May 
23, 1945. Div. 15-331. 1-M6 

694. Barrage Suitability of AN/ APT-5, J. F. Youngblood, 

Report 411-196, Projects RP-336 and AC-298.04, Har- 
vard University, Radio Research Laboratory, June 8, 
1945. Div. 15-322.123-M3 

695. C1906 Azimuth Homing System {Navy AN / APA-48), 

John W. Christensen, Report 411-198, Projects RP-209 
and NS-202, Harvard University, Radio Research Lab- 
oratory, June 28, 1945. Div. 15-313.1 11-Ml 

696. Flight Tests of G1151 Dispenser, D. A. Peterson, Report 
411-199, Projects RP-406 and AC-71, Harvard Univer- 
sity, Radio Research Laboratory, June 5, 1945. 

Div. 15-243-M2 

697. Filter Mismatch Loss with Improper Termination, Sey- 
mour B. Cohn and Paul I. Richards, Report 411-201, 
Projects RP-442 and SC-90.12, Harvard University, 
Radio Research Laboratory, June 12, 1945. 

Div. 15-360- Ml 

698. Graphs Useful in Determining Optimum Height of Jam- 
ming Antennas, H. Clark and E. F. Shaw, Report 
411-202, Projects RP-299 and SC-94.22, Harvard Uni- 
versity, Radio Research Laboratory, Aug. 13, 1945. 

Div. 15-332.M3 

699. Modifications of the AN- 148- A Antenna for RCM Use in 

the 200 MC Region, J. Margolin, Report 411-203, 
Project RP-481, Harvard University, Radio Research 
Laboratory, July 2, 1945. Div. 15-332. 16-Ml 

700. Radiation Characteristics of the Modified AN-148-A 

Antenna, M. P. Klein, Report 411-203A, Project RP- 
481, Harvard University, Radio Research Laboratory, 
Aug. 8, 1945. Div. 15-332. 16-M2 

701. Jamming Effectiveness of APT-4 {XA-2) against Small 

Wurzburg and Synthetic Giant Wurzburg, D. F. Wartzok, 
Report 411-204, Projects RP-338 and AC-294.12, Har- 
vard University, Radio Research Laboratory, July 12, 
1945. Div. 15-322. 15-M5 

702. Jamming Effectiveness of APT-4 against SCR-545-A, 

D. F. Wartzok, Report 411-204A, Projects RP-338 and 
AC-294.12, Harvard University, Radio Research Lab- 
oratory, Sept. 20, 1945. Div. 15-322. 15-M6 

703. AJJ Study of AN / APQ-5B Lab Attachment, F. P. 

Cowan, K. A. Davis, and J. H. Woodruff, H, Report 
411-205, Projects RP-452 and AC-292.03, Harvard Uni- 
versity, Radio Research Laboratory, June 15, 1945. 

Div. 15-221. 21-M5 

704. Low-Frequency Modification of the Rug Transmitter, 
AN /APQ-2, E. A. Yunker, Report 411-206, Projects 
RP-164 and AC-294.28, Harvard University, Radio 
Research Laboratory, June 23, 1945. 


705. An A/ J Measure for Use against Circularly Polarized 

Jamming, J. H. Woodruff, H, A. Keck, and Richard S. 
O’Brien, Report 411-207, Projects AC-292.01, NA-218, 
and RP-214, Harvard University, Radio Research Lab- 
oratory, June 20, 1945. Div. 15-222. 1-M13 

706. Modification of AN/APA-42 for Bottom Mounting in 
B-29, John J. Wittkopf, Report 411-208, Projects 
RP-298 and AC-297.07, Harvard University, Radio 
Research Laboratory, July 23, 1945. 

Div. 15-313.14-M3 

707. An R-F Wattmeter for the 1000 Mc-3000 Me Range, W. R. 

Rambo, Report 411-209, Projects RP-169 and , AC- 
294.20, Harvard University, Radio Research Labora- 
tory, June 22, 1945. Div. 15-521. 12-M2 

708. Design Considerations and Characteristics of M2 900 

Antennas, E. L. Bock, Report 411-210, Projects RP-138 
and NS-204, Harvard University, Radio Research Lab- 
oratory, July 13, 1945. Div. 15-332. 25-M2 

709. Properties of Ridge Wave Guide, Seymour B. Cohn, 

Report 411-211, Projects RP-442, AC-290.12, and 
AC-290.16, Harvard University, Radio Research Lab- 
oratory, Aug. 15, 1945. Div. 15-37 1.1-M9 

710. Adaptation of AS- 16 1 / ART and AS-97 / ART Whip 

Antennas as Horizontally-Polarized Radiators in the 75 
Me Region, David Lazarus, Report 411-212, Project 
RP-306, Harvard University, Radio Research Labora- 
tory, June 28, 1945. Div. 15-332. 18-M2 

711. Method of Installation and Pattern Measurement of 
C1950 Series Homing Antennas {AN/ APA-48) in Vari- 
ous Type Aircraft, John W. Christensen, Report 411-213, 
Projects RP-209 and NS-202, Harvard University, 
Radio Research Laboratory, Sept. 11, 1945. 

Div. 15-331. 1-M7 

712. A Report on the Susceptibility to Jamming of the AN/ 

APG-1 Radar, J. H. Woodruff, H, and F. P. Cowan, 
Report 411-214, Projects RP-368 and AC-292.03, Har- 
vard University, Radio Research Laboratory, July 5, 
1945. Div. 15-221.21-M6 

713. Jamming Susceptibility of the AN /APS-4 {ASH) Radar 

and the APA-16 Bombing Attachment, Ralph H. Hog- 
lund. Report 411-215, Projects RP-411 and NA-219, 
Harvard University, Radio Research Laboratory, July 
14, 1945. Div. 15-221. 21-M7 

714. Performance of the AS-251 / AP {M2204) Antenna Sys- 

tem When Mounted in Metallic Recesses, John Allen, 
Report 411-216, Projects RP-303, AC-290.14, and 
AC-294.17, Harvard University, Radio Research Lab- 
oratory, Sept. 19, 1945. Div. 15-332. 11-M5 

715. An Armored Steel Cable with Low Radar Reflectivity, 
Felix Bloch, Report 411-217, Projects RP-349 and 
AC-298.11 (AC-84), Harvard University, Radio Re- 
search Laboratory, July 20, 1945. 

Div. 15-821-Ml 

716. Performance and Applications of the M2914 Relay, G. 

Stavis, Report 411-218, Projects RP-138 and NS-204, 
Harvard University, Radio Research Laboratory, July 
23, 1945. Div. 15-332.25-M3 

717. A/J Evaluation of AN /TPL-1, Hi O. Anger, Report 
411-219, Projects RP-453 and SC-92.11, Harvard Uni- 
versity, Radio Research Laboratory, Aug. 1, 1945. 

Div. 15-221. 23-M4 


Div. 15-322.11-Ml 


BIBLIOGRAPHY 


491 


718. Radar Video Analyzer, C. C. Loomis, Report 411-220, 
Projects RP-462b and NS-394.10, Harvard University, 
Radio Research Laboratory, Aug. 1, 1945. 

Div. 15-311.23-Ml 

719. A Broadband Directional Pickup and Wattmeter for 
Waveguide, H. C. Early, Report 411-221, Projects 
RP-461a and NS-394.10, Harvard University, Radio 
Research Laboratory, Aug. 1, 1945. 

Div. 15-371. 1-M8 

720. Report on RRL Project A-500 {Tuba), E. S. Welch, Jr., 

J. J. Livingood, and W. W. Salisbury, Report 411-222, 
Project RP-lOO, Harvard University, Radio Research 
Laboratory, Aug. 13, 1945. Div. 15-402. 1-M3 

721. Modifications of the AM-33/ ART Amplifier, W. R. 

Rambo and G. R. Bridgeford, Report 411-223, Project 
RP-344, Harvard University, Radio Research Labora- 
tory, Sept. 11, 1945. Div. 15-322. 21-M6 

722. Misdirection of Lobed Radar by Mechanical Means, 

Robert Weinstock, Report 411-224, Projects RP-406e 
and AC-296.01, Harvard University, Radio Research 
Laboratory, Aug. 7, 1945. Div. 15-241. 3-M5 

723. The Equalization of Noise Amplifiers, J. R. Curry, 

Report 411-225, Projects RP-187a and SC-94.16, Har- 
vard University, Radio Research Laboratory, Aug. 6, 
1945. Div. 15-526-M2 

724. Airborne Jamming Tests against A I Radars, John J. 

Wittkopf, Report 411-226, Projects NA-224 and RP- 
459, Harvard University, Radio Research Laboratory, 
Aug. 11, 1945. Div. 15-221.4-M5 

725. Field Test of Crash Model C-1906 Homing Device, John 

J. Wittkopf, Report 411-227, Projects RP-209 and 
NS-397.10, Harvard University, Radio Research Lab- 
oratory, Aug. 11, 1945. Div. 15-313. 111-M2 

726. RCM against Radar Blind Bombing Equipment, Morton 
Hamermesh and Robert Weinstock, Report 411-228, 
Projects RP-474 and SC-98.10, Harvard University, 
Radio Research Laboratory, Sept. 5, 1945. 

Div. 15-221. 13-M2 

727. An All-Metal Dummy Load for Waveguide, H. C. Early, 

Report 411-229, Projects RP-461 and NS-394.10, Har- 
vard University, Radio Research Laboratory, Oct. 25, 
1945. Div. 15-371. 1-Mll 

728. Silent Knight, James M. Moran, Report 411-230, 
Projects RP-448 and AC-290.16, Harvard University, 
Radio Research Laboratory, Aug. 20, 1945. 

Div. 15-31 1.124-M4 

729. A Report on the Susceptibility to Jamming of the SCR-545, 

J. H. Woodruff, 1 1, H. O. Anger, and K. A. Davis, 
Report 411-231, Projects RP-475 and SC-92.12, Har- 
vard University, Radio Research Laboratory, Sept. 5, 
1945. Div. 15-221. 23-M5 

730. Oscillations and Noise in Hot- Cathode Arcs, J. D. Cobine, 

C. J. Gallagher, R. Weinstock, and Felix Bloch, Report 
411-232, Projects RP-187, RP-181, and SC-94.16, Har- 
vard University, Radio Research Laboratory, Sept. 26, 
1945. Div. 15-343.22-M2 

731. The M6120 Broad-Band Antenna Spinner for the M4100 

{DBM) Direction Finding System, J. D. Kraus, H. K. 
Clark, and S. Beraducci, Report 411-233, Projects RP- 
271 and NS-202, Harvard University, Radio Research 
Laboratory, Sept. 8, 1945. Div. 15-331. 4-Ml 


732. Rhume of UHF Filter Development, Seymour B. Cohn 
and Paul I. Richards, Report 411-234, Projects RP-442, 
AC-290.12, and AC-290.16, Harvard University, Radio 
Research Laboratory, Sept. 10, 1945. Div. 15-361-M4 

733. Modulation Tests of the 6J21 Magnetron, J. C. Turnbull, 
J. R. Duggan, C. F. Otis, and H. W. Welch, Report 
411-235, Projects SC-94.25 and RP-417, Harvard Uni- 
versity, Radio Research Laboratory, Oct. 29, 1945. 

Div. 15-341. 4-M9 

734. Window Developments, F. L. Whipple, Morton Hamer- 

mesh, D. W. Taylor, A. T. Goble, A. W. Tyler, and Felix 
Bloch, Report 411-236, Projects RP-103 and AC-69, 
Harvard University, Radio Research Laboratory, Dec. 
4, 1945. Div. 15-241-M7 

735. R-F Conductors and Fittings, J. G. C. Swinney, Jr., 
Report 411-237, Project RP-472, Harvard University, 
Radio Research Laboratory, Sept. 11, 1945. 

Div. 15-371. 3-M2 

736. The Appraisal of RCM through the Examination of 

Battle Damage, David A. Park, Report 411-238, Project 
RP-299, Harvard University, Radio Research Labora- 
tory, Sept. 10, 1945. Div. 15-710-M2 

737. Cold-Cathode Gas-Tube Noise Generators, Stanley Ruth- 

berg, Report 411-239, Projects RP-187 and SC-94.16, 
Harvard University, Radio Research Laboratory, Sept. 
13, 1945. Div. 15-343.21-M5 

738. The Universal Characteristics of Triple-Resonant- Circuit 

Band-Pass Filters, Karl R. Spangenberg, Report 411- 
240, Projects RP-442, AC-290.12, and AC-290.16, Har- 
vard University, Radio Research Laboratory, Sept. 25, 
1945. Div. 15-360-M2 

739. McNally Tubes in Radial Cavities, J. J. Wedel, Report 
411-241, Project RP-286, Harvard University, Radio 
Research Laboratory, Sept. 11, 1945. 

Div. 15-351. 1-M3 

740. A Photographic-PPI Method of Model Antenna Pattern 
Measurement, John W. Christensen, Report 411-242, 
Projects RP-481 and AC-290.14, Harvard University, 
Radio Research Laboratory, Sept. 10, 1945. 

Div. 15-333.21-MlO 

741. M6700 Shipborne DF Antenna, G. Stavis, Report 

411-243, Projects RP-271, NS-202, and NS-397.07, 
Harvard University, Radio Research Laboratory, Sept. 
11, 1945. Div. 15-331.4-M2 

742. Video Transformers for Noise Voltage, J. D. Cobine, 
J. R. Curry, C. J. Gallagher, and S. Ruthberg, Report 
411-244, Projects RP-187 and SC-94.16, Harvard Uni- 
versity, Radio Research Laboratory, Oct. 30, 1945. 

Div. 15-381. 1-M6 

743. Proposed Field Tests of AN / APS-4 Radar, Ralph H. 

Hoglund and F. P. Cowan, Report 411-245, Projects 
RP-411 and NA-219, Harvard University, Radio Re- 
search Laboratory, Sept. 12, 1945. Div. 15-221. 21-M9 

744. Microwave Wattmeter, Charles F. Hadley, Report 411- 
246, Projects RP-306 and AC-299.06, Harvard Univer- 
sity, Radio Research Laboratory, Sept. 25, 1945. 

Div. 15-521. 11-M2 

745. A Self- Calibrating Thermistor Bridge, L. A. Manning, 

Report 411-247, Projects RP-306 and AC-299.07, Har- 
vard University, Radio Research Laboratory, Sept. 13, 
1945. Div. 15-521. 11-Ml 


492 


BIBLIOGRAPHY 


746. Laboratory Studies of Jamming Effectiveness, Donald W. 

Taylor, Report 411-248, Projects AC-296.01 and RP- 
103, Harvard University, Radio Research Laboratory, 
Oct. 17, 1945. Div. 15-221.31-M2 

747. The Construction of the Donutron, a Tunable Squirrel- 
Cage Magnetron, M. D. Hare and Virginia Leonard, 
Report 411-249, Project RP-295, Harvard University, 
Radio Research Laboratory, Oct. 26, 1945. 

Div. 15-341. 1-M3 

748. Measurements of Jamming Effectiveness, R. L. Henkel, 
T. S. Kuhn, L. B. Lusted, and R. E. Reid, Report 
411-250, Projects AC-294.12 and RP-338, Harvard 
University, Radio Research Laboratory, Sept. 21, 1945. 

Div. 15-221.31-Ml 

749. The Calculation of Electronic Jamming Performance 

against GL and SLC Radars, R. D. Sard and David A. 
Park, Report 411-251, Projects RP-299, AC-294.22, and 
SC-94.22, Harvard University, Radio Research Lab- 
oratory, Nov. 16, 1945. Div. 15-230-Ml 

750. A Tunable Squirrel-Cage Magnetron, The Donutron, 
F. H. Crawford and M. D. Hare, Report 411-252, 
Project RP-295, Harvard University, Radio Research 
Laboratory, Oct. 1, 1945. 

Div. 15-341. 1-M2 

751. Attenuation in Waveguide at 3000 Me Due to Moisture 

Condensation, Paul A. Pearson, Report 411-253, Project 
R P-481, Harvard University, Radio Research Labora- 
tory, Oct. 2, 1945. Div. 15-371. 1-MlO 

752. Supplementary Report on Low-Frequency Modification 
of the Rug Transmitter {AN /APQ-2), James L. Clark, 
Report 411-254, Project RP-164, Harvard University, 
Radio Research Laboratory, Sept. 25, 1945. 

Div. 15-322.1 1-M2 

753. Measurements on Wide- Band Coaxial Lines, J. C. Turn- 
bull, J. R. Duggan, and R. W. Green, Report 411-255, 
Projects RP-405 and SC-94.25, Harvard University, 
Radio Research Laboratory, Sept. 26, 1945. 

Div. 15-371. 2-M2 

754. The E3200 X-Band Jamming System, R. E. Kell, Report 
411-256, Projects RP-221 and NA-156, Harvard Uni- 
versity, Radio Research Laboratory, Sept. 26, 1945. 

Div. 15-404- M3 

755. The P102 Pulse- Amplitude Recorder and Time Marker, 

Raymond K. Vermillion, Report 411-257, Project RP- 
299, Harvard University, Radio Research Laboratory, 
Sept. 28, 1945. Div. 15-221.4-M6 

756. 6D4 Spectrum Checker, P. S. Jastram and C. J. Gal- 

lagher, Report 411-258, Projects RP-187 and SC-94.16, 
Harvard University, Radio Research Laboratory, Sept. 
28, 1945. Div. 15-343.241-Mll 

757. Resume of Ultra High Frequency Tuned-Circuit Preselec- 

tors, Seymour B. Cohn and Paul 1. Richards, Report 
411-259, Projects RP-442, AC-290.12, and AC-290.16, 
Harvard University, Radio Research Laboratory, Jan. 
11, 1946. Div. 15-311. 21-M8 

758. The Circuit Theory of Noise, P. S. Jastram, Report 411- 
260, Projects RP-187 and SC-94.16, Harvard Univer- 
sity, Radio Research Laboratory, Nov. 1, 1945. 

Div. 15-526-M3 

759. A Noise Analyzer Using a Commercial Communications 
Receiver, J. R. Duggan, Report 411-262, Projects RP- 


461, SC-94.25, and NS-394.10, Harvard University, 
Radio Research Laboratory, Sept. 26, 1945. 

Div. 15-515-M4 

760. Slot-Antenna Development at Radio Research Laboratory, 

David Lazarus, Report 411-263, Projects RP-303 and 
AC-294.17, Harvard University, Radio Research Lab- 
oratory, Nov. 17, 1945. Div. 15-333. 53-M3 

761. An Approximate Theory of Eddy-Current Loss in Trans- 

former Cores Excited by Sine Wave or by Random Noise, 
David M. Middleton, Report 411-264, Projects RP-187 
and SC-94.16, Harvard University, Radio Research 
Laboratory, Oct. 25, 1945. Div. 15-381. 1-M5 

762. AN ! APQ-20 Spot- Jamming System, Warren D. White 
and James L. Clark, Report 411-265, Projects RP-424, 
AC-294.20, and NA-189, Harvard University, Radio 
Research Laboratory, Oct. 1, 1945. 

Div. 15-401. 3-M3 

763. The S5000 Spot- Jamming System, Warren D. White and 
James L. Clark, Report 411-266, Projects RP-424, 
AC-294.20, and NA-189, Harvard LTniversity, Radio 
Research Laboratory, Oct. 1, 1945. 

Div. 15-401. 3-M4 

764. The Electrical Characteristics of the D9081 and Q1248 
X-Band Oscillator, Howard M. Zeidler, Report 411-268, 
Projects RP-286 and AC-290.12, Harvard University, 
Radio Research Laboratory, Dec. 14, 1945. 

Div. 15-351. 1-M4 

765. The Low-Frequency Elephant Transmitter, W. R. Rambo, 

Report 411-270, Projects RP-461, SC-94.25, and NS- 
394.10, Harvard University, Radio Research Labora- 
tory, Oct. 22, 1945. Div. 15-403.2-Ml 

766. The Effect of Signal- Intercept Probabilities on Search- 

Receiver Design, George E. Hulstede, Report 411-272, 
Project RP-286, Harvard University, Radio Research 
Laboratory, Oct. 10, 1945. Div. 15-31 1.5-M2 

767. Nonlinear Limiter Circuits for Use with Intensity- 
Modulated Indicators, E. R. Brill, Report 411-274, 
Projects RP-406 and SC-92.01, Harvard University, 
Radio Research Laboratory, Aug. 1, 1945. 

Div. 15-383-M8 

768. Techniques of Cathode-Ray Tube Photography Used for 

Radar Scopes, C. Gray and S. W. Athey, Report 411- 
276, Harvard University, Radio Research Laboratory, 
Feb. 5, 1946. Div. 15-221. 13-M4 

769. Development of the U1500 Standard Signal Generator for 
the Frequency Range, 1800-4000 Megacycles {TS-403/U), 
W. B. Wholey, Report 411-277, Projects RP-469, 
AC-299.07, and NA-223, Harvard University, Radio 
Research Laboratory, Oct. 22, 1945. 

Div. 15-512-M12 

770. Experimental Determination of Formation Factor, J. F. 

Youngblood and B. M. Kuck, Report 411-278, Project 
RP-299, Harvard University, Radio Research Labora- 
tory, Oct. 22, 1945. Div. 15-221. 13-M3 

771. Notes on Receiver Sensitivity, H. W. Belles, Harold L. 

Crispell, and F. Malcolm Gager, Report 411-279, Har- 
vard University, Radio Research Laboratory, Oct. 29, 
1945. Div. 15-527-M2 

772. Measurement of Radio- Frequency Power by the Coaxial 
Thermocouple-Lossy Line Method, R. R. Rhiger, F. 
Malcolm Gager, and J. R. Marshall, Report 411-280, 


BIBLIOGRAPHY 


493 


Project RP-409, Harvard University, Radio Research 
Laboratory, Oct. 25, 1945. Div. 15-521. 3-M4 

773. Measurement of Radio- Frequency Power by the Equiv- 

alent Signal Method, Harold L. Crispell, Report 411- 
280A, Harvard University, Radio Research Laboratory, 
Nov. 9, 1945. Div. 15-521-M2 

774. Measurement of Attenuation of Microwave Filters, R. R. 
Rhiger and F. Malcolm Gager, Report 411-281, Harvard 
University, Radio Research Laboratory, Oct. 24, 1945. 

Div. 15-523-Ml 

775. AN / APA-42-T1 Direction Finding Antenna Trainer, 

0. W. Whitby, Report 411-282, Projects RP-471 and 
AC-298.10, Harvard University, Radio Research Lab- 
oratory, Oct. 26, 1945. 

Div. 15-660-Ml 

776. Circularly Polarized Search Antennas for the Band 2100 

to 4000 Me, R. M. Hatch, Jr. and C. C. Loomis, Report 
411-283, Projects RP-303, NS-394.10, and NS-394.18, 
Harvard University, Radio Research Laboratory, Oct. 
31, 1945. Div. 15-331.31-M4 

777. Self-Regulating Field Excitation for C-W Magnetrons, 
H. C. Early and H. W. Welch, Report 411-284, Projects 
RP-461, SC-94.25, and NS-394.10, Harvard University, 
Radio Research Laboratory, Oct. 31, 1945. 

Div. 15-341.6-M7 

778. A High-Speed Sweep Generator with Sectional Scan, Ray- 
mond K. Vermillion, Report 411-285, Project RP-306, 
Harvard University, Radio Research Laboratory, Nov. 

1, 1945. Div. 15-383-M9 

779. Summary Report on Cl 600 Moth, AN / APQ-14, John W. 

Christensen, Report 411-286, Projects RP-188 and 
SC-49, Harvard University, Radio Research Labora- 
tory, Oct. 30, 1945. Div. 15-830-M2 

780. M6600 X-Band Antenna and Drive Assembly for Use 
with M3000 {AN / APA-17) Airborne Direction Finder, 
E. C. Barkofsky, Report 411-287, Projects RP-298, 
NS-202, and NS-397.07, Harvard University, Radio 
Research Laboratory, Nov. 19, 1945. 

Div. 15-331. 2-M5 

781. Heterodyne Frequency Meter for 55-1000 Me, C. D. 
Jeffries, Report 411-289, Project RP-245, Harvard Uni- 
versity, Radio Research Laboratory, Nov. 15, 1945. 

■ Div. 15-514-M3 

782. Shipborne Trials of the X-MBT Radar Intercept and 
Jamming System, J. W. Kearney, Report 411-290, 
Projects RP-457, SC-94.25, and NS-394.10, Harvard 
University, Radio Research Laboratory, Jan. 18, 1946. 

Div. 15-403.2-M2 

783. Report on M4000 Antennas, J. A. Nelson, Report 411- 
291, Projects RP-303 and SC-94.15, Harvard Univer- 
sity, Radio Research Laboratory, Jan. 3, 1946. 

Div. 15-332.121-M2 

784. Notes on Spectrum Analysis, J. C. Riley, Report 411-292, 

Harvard University, Radio Research Laboratory, Nov. 
24, 1945. Div. 15-513-M13 

785. Voltage- Standing-Wave-Ratio Measuring Equipment, J. 
R. Marshall, Report 411-293, Harvard University, 
Radio Research Laboratory, Nov. 26, 1945. 

Div. 15-525-M3 

786. Technical Report on the M4905 S-Band Airborne Cir- 
cularly Polarized Radiator, P. M. Keeler, Report 411- 


294, Projects RP-303 and AC-294.17, Harvard Univer- 
sity, Radio Research Laboratory, Nov. 26, 1945. 

Div. 15-332. 15-M2 

787. 60-300 Me Power Oscillator with Single-Dial Tuning 
Control, J. Gregg Stephenson and Milton B. Adams, 
Report 411-295, Project RP-346, Harvard University, 
Radio Research Laboratory, Dec. 14, 1945. 

Div. 15-351. 2-M7 

788. The AN j APQ-21 Airborne System, W. R. Rambo, 
Report 411-296, Projects RP-455, AC-294.20, and 
NA-189, Harvard University, Radio Research Labora- 
tory, Dec. 14, 1945. 

Div. 15-401. 3-M5 

789. M7 100 Direction Finder, H. K. Clark, W. D. McGuigan, 
and C. A. Mizen, Report 411-297, Projects RP-271, 
NS-397.09, and NS-202, Harvard University, Radio Re- 
search Laboratory, Jan. 10, 1946. 

Div. 15-313.23-Ml 

790. Fish-Hook Antenna, Andrew Alford, Report 411-298, 
Projects RP-303 and SC-83, Harvard University, Radio 
Research Laboratory, Mar. 6, 1946. 

Div. 15-332. 11-M6 

791. Administrative History of Radio Research Laboratory 

Operating under Division 15 of the National Defense 
Committee, Contract OEMsr-411, 20, March 1942 to 1, 
January 1945, F. E. Terman and Oswald G. Villard, Jr., 
Report 411-299, Harvard University, Radio Research 
Laboratory, Mar. 21, 1946. Div. 15-120-Ml 

792. AJ High-Pass Filters, Oswald G. Villard, Jr., Report 
E 602-Rl, Harvard University, Radio Research Lab- 
oratory, Nov. 18, 1942 (Revised Dec. 23, 1942). 

793. Note on the Design of High Pass Filters for the Reduction 
of Interference from Jamming Signals Modulated at a Low 
Frequency, Oswald G. Villard, Jr., Report E 602-R2, 
Harvard University, Radio Research Laboratory, Dec. 
30, 1942. 

794. Preliminary Operating Instructions for E-1610 Plug-in 
A/J High-Pass Filter, 411-IB-24, Harvard University, 
Radio Research Laboratory, Mar. 16, 1944. 

Div. 15-222.1-M5 

795. Preliminary Operating Instructions for E-IlOj 12 Plug-in 
A/J High-Pass Filter and Receiver A/J Modification, 
R. E. Kell, 411-IB-14, Project RP-223, Harvard Uni- 
versity, Radio Research Laboratory, Jan. 18, 1945. 

Div. 15-222.1-Mll 

796. A 1700 Jamming Signal Generator, Ralph H. Hoglund, 
411-IB-18, Project RP-191, Harvard University, Radio 
Research Laboratory, Mar. 15, 1944. 

Div. 15-620-M2 

797. Preliminary Operating Instructions for F4100 Training 
Oscillator, Elton Barrett, 411-IB-22, Harvard Univer- 
sity, Radio Research Laboratory, Mar. 1, 1944. 

Div. 15-610.1-M2 

798. Handbook of Maintenance Instructions for F3800 Trans- 

mitter {AN / UPT /T4), 411-IB-61, Project RP-323, Har- 
vard University, Radio Research Laboratory, Feb. 23, 
1945. Div. 15-610-M2 

799. F-4100 Training Oscillator, R. B. Monroe and E. J. 
Berggren, 411-TR-17, Harvard University, Radio Re- 
search Laboratory, Mar. 21, 1944. 

Div. 15-610. 1-M3 


494 


BIBLIOGRAPHY 


800. General Radio P525-A Signal Generator, R. R. Rhiger, 
411-TR-23, Harvard University, Radio Research Lab- 
oratory, May 12, 1944. 

Div. 15-620-M3 

801. Test Report {Test and Standards Division) P-525A 

Signal Generator, F. Malcolm Gager, 411-TR-23B, 
Harvard University, Radio Research Laboratory, Mar. 
8, 1945. Div. 15-512-MlO 

802. F-2800 Carpet Practice Jammer, Harold L. Crispell, 
411-TR-27, Harvard University, Radio Research Lab- 
oratory, May 18, 1944. 

Div. 15-640-Ml 

803. Test Report ( T est and Standards Division) T -42/ UPT-Tl 
Practice Jammer, R. B. Monroe, 411-TR-27A, Harvard 
University, Radio Research Laboratory, July 19, 1944. 

Div. 15-640-M2 

804. Test Report {Test and Standards Division) U-700 Jam- 
ming Signal Generator, F. Malcolm Gager, 411-TR-42, 
Harvard University, Radio Research Laboratory, Sept. 

25, 1944. Div. 15-512-M8 

805. Test Report {Test and Standards Division) U-700 Jam- 
ming Signal Generator, F. Malcolm Gager, 411-TR-42A, 
Harvard University, Radio Research Laboratory, Jan. 

26, 1945. Div. 15-512-M9 

806. Intelligence Information on RCM Effectiveness in the 

E.T.O., Richard S. O’Brien and R. A. Soderman, Report 
1045-MR-15, Project RP-987, Harvard University, 
ABL, June 16, 1945. Div. 15-711-M2 

807. Calculations of Jamming Range of Cigar and Tuba, 
E. Fubini and T. Kuhn, Report G 604-Rl, Harvard 
University, Radio Research Laboratory, July 23, 1943. 

808. Noise Conference at Radio Research Laboratory, Harvard 
University, Radio Research Laboratory, Oct. 19, 1943 
(an unnumbered report published at RRL for NDRC). 

Div. 15-343.1-M4 

809. Very High Frequency Techniques, Radio Research Lab- 
oratory of Harvard University, McGraw-Hill Book 
Company, 1947. 

810. Preliminary Instruction Book for the D1203 Panoramic 

Spectrum Analyzer RRL Production Model, 411-IB-39A, 
Project RP-175, Harvard University, Radio Research 
Laboratory, Oct. 10, 1944. Div. 15-513-M7 

811. Handbook of Maintenance Instructions for U-800 Test 
Oscillator, 411-IB-78, Project RP-306, Harvard Uni- 
versity, Radio Research Laboratory, Mar. 29, 1945. 

Div. 15-511-M4 

812. Preliminary Handbook of Maintenance Instructions for 

UllOl Test Signal Generator, TS-406 {XR-1) / UP, 411- 
IB-88, Projects RP-476, AC-299.07, and NA-223, Har- 
vard University, Radio Research Laboratory, July 14, 
1945. Div. 15-512-Mll 

813. Instructions for Operation of the F4000 Wavemeter, 411- 

IB-35, Harvard University, Radio Research Labora- 
tory, June 1, 1944. Div. 15-525-Ml 

814. Preliminary Handbook of Maintenance Instructions for 
the U700 Signal Generator [Rat, MK6 {XR) ], 411-IB- 
77, Projects RP-364 and NO-218, Harvard University, 
Radio Research Laboratory, Oct. 3, 1945. 

Div. 15-620-M5 

815. Supplemental Instruction Book for Installing the Navy 
Type C AOS- 50 AEY I-F to Video Converter on the 


SCR-296 Radar, 411-IB-56, Project RP-224, Harvard 
University, Radio Research Laboratory, Oct. 26, 1944. 

Div. 15-222.1-MlO 

816. Test Specification for AN / APQ-1 Carpet Sweeper, R. B. 
Monroe and R. R. Rhiger, TS-7, Harvard University, 
Radio Research Laboratory, Aug. 24, 1943. 

Div. 15-401. 1-Ml 

817. Preliminary Instructions for Elephant, 411-IB-51, Proj- 
ects RP-457, SC-94.25, and NS-394.10, Harvard Uni- 
versity, Radio Research Laboratory, Mar. 26, 1946. 

Div. 15-403.2-M3 

818. Preliminary Instructions for F3702 Antenna {AS-145/ 
SPT-6), 411-IB-58, Project RP-138, Harvard Univer- 
sity, Radio Research Laboratory, Feb. 2, 1945. 

Div. 15-332.21-M2 

819. Preliminary Instructions for F3903 Antenna {AS-263/ 
UPT), 411-IB-70, Project RP-138, Harvard University, 
Radio Research Laboratory, Mar. 7, 1945. 

Div. 15-332.22-Ml 

820. Preliminary Handbook of Maintenance Instructions for 
the F47 00 Antenna {AS-236/ SPT), 411-IB-85, Projects 
RP-138 and NS-204, Harvard University, Radio Re- 
search Laboratory, Aug. 7, 1945. 

Div. 15-332. 23-Ml 

821. Assembly and Installation Instructions for the M2803 and 

M2804 Antenna Systems, J. Margolin, 411-IB-33, Har- 
vard University, Radio Research Laboratory, June 2, 
1944. Div. 15-332. 12-Ml 

822. Preliminary Instruction Sheet for the M-3301 Antenna, 
Clare Driscoll, 411-IB-46, Project RP-303, Harvard 
University, Radio Research Laboratory, Feb. 5, 1945. 

Div. 15-332. 14-M2 

823. Preliminary Instruction Sheet on the M2204 Antenna, 
J. A. Nelson and C. Milton Daniell, 411-IB-65, Project 
RP-303, Harvard University, Radio Research Labora- 
tory, Feb. 13, 1945. 

Div. 15-332.11-M3 

824. Preliminary Instruction Book for the M4902 Airborne 
S Band Circularly-Polarized Radiator, J. G. C. Swinney, 
Jr., 411-IB-71, Project RP-303, Harvard University, 
Radio Research Laboratory, Mar. 12, 1945. 

Div. 15-332.15-Ml 

825. Preliminary Instructions for the M2404 {SA-14/ SPR-1) 
and M2413 {SA-44/APR) RF Switches, John H. Jasberg 
and E. L. Bock, 411-IB-44, Project RP-138, Harvard 
University, Radio Research Laboratory, Jan. 11, 1945. 

Div. 15-372.1-Ml 

826. Preliminary Instructions for the M2415 RF Switch 
{SW-44A/APR), John H. Jasberg and E. L. Bock, 
411-IB-41, Project RP-138, Harvard University, Radio 
Research Laboratory, Feb. 1, 1945. 

Div. 15-372.1-M2 

827. Preliminary Instruction Book for the D2100 Receiver 
{AN/APR-7A), 411-IB-49, Project RP-408, Harvard 
University, Radio Research Laboratory, Oct. 17, 1944. 

Div. 15-311. 126-Ml 

828. Preliminary Instruction Book for M6200 {AS-222/APA- 
17) Antenna System, H. K. Clark, S. Beraducci, and 
J. D. Kraus, 411-IB-90, Project RP-298, Harvard Uni- 
versity, Radio Research Laboratory, Apr. 19, 1945. 

Div. 15-331. 2-M3 


BIBLIOGRAPHY 


495 


829. Operation and Maintenance of M6400 Antenna System, 

H. K. Clark, 411-IB-86, Projects RP-298 and NS-202, 
Harvard University, Radio Research Laboratory, Aug. 

26, 1945. Div. 15-331. 2-M4 

830. Instruction Book for H300 Noise Analyzer, James H. 
Eldredge, Jr., 411-IB-3, Project RP-306, Harvard Uni- 
versity, Radio Research Laboratory, Nov. 12, 1943. 

Div. 15-515-Ml 

831. The Operational Use of ROM in the ETO, Report 1045-14, 
Harvard University, ABL, Oct. 1, 1945. 

Div. 15-711-M3 

832. Radio Proximity Fuse for Plane-to-Plane Rocket Applica- 
tion, Diamond, Hinman, Huntoon, Brunette, and Page, 

NDRC Armor and Ordnance Report A-144, Feb. 5, 

1943. 

833. Articulation Testmg Methods, H. Fletcher and J. C. 
Steinberg, Bell System Technical Journal, October 1929. 

834. Memorandum on the Energy- Frequency Distribution in a 
Noise- Modulated FM Wave, A. D. Fowler, Bell Tele- 
phone Laboratories, Case 3430-ADF-OE, July 28, 1942. 

835. S. O. Rice, Bell System Technical Journal, Vol. 23, 
p. 282 (1944); and Vol. 24, p. 46 (1945). 

836. D. O. North, RCA Technical Report PTR-6C, June 25, 

1943. 

837. S. A. Goudsmit, Radiation Laboratory (MIT), Report 
43-21, January 29, 1943. 

838. W. H. Jordan, Radiation Laboratory (MIT), Report 
61-23, July 6, 1943. 

839. Echoing Properties of Long Strips and Separate and Tied 
Resonant Strips, Mathematics Group, T.R.E., OSRD 
Liaison Office 11-5-7396(8), T.R.E. Report T-1548, 

Sept. 30, 1945. Div. 15-241. 2-Ml 

840. The Reflection of Electromagnetic Waves by Long Wires 
and Non-Resonant Cylindrical Conductors, J. M. C. 

Scott and T. Pearcey, OSRD Liaison Office WR-1459, 

Report CRB-45/49, R.R.D.E. Report 259, Nov. 14, 

1944. Div. 15-241.2-M7 

841. The Application of Corner Reflectors to Radar, R. D. 

O’Neal, F. S. Holt, and P. D. Crout, Radiation Lab- 
oratory Report 43-31, May 14, 1943. 

842. Optical Theory of the Corner Reflector, R. C. Spencer, 
Radiation Laboratory Report 433, Mar. 2, 1944. 

843. L. Brillouin, AMP Report 129 I R AMG-C Report 229, 

1944. 

844. B. van der Pol, Proc. I.R.E., Vol. 18, p. 1194, 1930. 864. 

845. Physik und Technik der Ultrakurzen Wellen, H. R. Holl- 
man, Vol. 1, Chapter 4, Springer, 1936. 

846. High Frequency Thermionic Tubes, A. F. Harvey, 

Chapters 4 and 5, John Wiley and Sons, 1943. 865. 

847. Voltage and Wavelength Scaling of Magnetrons, A. M. 
Clogston, Radiation Laboratory Group 52, Special Re- 
port, Jan. 21, 1943. 

848. A 30 Me Schering Bridge, Y. Beers, Radiation Labora- 866. 
tory Report 61-19, May 12, 1943. 

849. A 60 Me Parallel Schering Bridge, Y. Beers, Radiation 

Laboratory Report 558, Apr. 22, 1944. 867. 

850. German Radar, T/L Division (RCM) O SIG O U.K. 

Base, Sept. 1, 1944. 

851. Frequency Charts on Jap Radio Equipment May 1944 & 

Jap Signal Services April 1944, Intelligence Branch 868. 
O C SIG O, April 1944 and May 1944. 


852. The Navy's Story of Radar Countermeasures (a press 

release), Nov. 29, 1945. ' * 

853. Elimination of Enemy Radar Interference from SCR- 
522-A Receiver BC-624-A, J. M. Hollywood, Report 
1045-1, Harvard University, ABL, Nov. 16, 1943. 

Div. 15-212.11-Ml 

854. Peter Tests for British Navy, Siegfried Hansen, Report 

1045-2, Project RP-156, Harvard University, ABL, 
Dec. 18, 1943. Div. 15-403.1-M3 

855. Modifications to Make RC-156-A Carpet Transmitter 
Operate in the 335-415 Me Band, J. T. Wilner, Report 
1045-3, OSRD Liaison Office WA-2151-la, Harvard 
University, ABL, Jan. 20, 1944. 

Div. 15-322. 124-M2 

856. Report of Peter Trials at Tantallon 17-25th March, 1944, 

Siegfried Hansen and H. H. Race, Report 1045-4, 
Project RP-156, Harvard University, ABL, Apr. 2, 
1944. Div. 15-403.1-M4 

857. Progress Report of the American British Laboratory 
Period Ending March 25, 1944, J. W. Dyer, Report 
1045-5, Harvard University, ABL, Mar. 25, 1944. 

Div. 15-124-Ml 

858. Report on Sleeve Antenna BC-900, R. F. Lewis and G. H. 

Klemm, Report 1045-6, Harvard University, ABL, 
Apr. 17, 1944. Div. 15-331. 14-Ml 

859. Report on Sleeve Antenna BC-500, R. F. Lewis and G. H. 

Klemm, Report 1045-7, Harvard University, ABL, Apr. 
17, 1944. Div. 15-331. 14-M2 

860. Modification of BC-639A Receiver to Reduce Pulse Inter- 

ference, G. P. McCouch, Report 1045-8, Harvard Uni- 
versity, ABL, May 17, 1944. Div. 15-212. 11-M5 

861. A Study of the RCM Requirements of the 8th and 9th Air 

Forces, W. E. Evans, Report 1045-9, Harvard Univer- 
sity, ABL, June 20, 1944. Div. 15-322. 124-M5 

862. Modification of British Ground Cigar for Spot Jamming, 
W. E. Evans, Report 1045-10, OSRD Liaison Office 
WA-3057-2, Harvard University, ABL, July 20, 1944. 

Div. 15-402. 2-M4 

863. Report of ABL Activities in Planning and Installations 
for RCM Phase of Operation Neptune {Invasion of 
Normandy), F. C. Cahill, Report 1045-11, Project RP- 
987, OSRD Liaison Office WA-3304-1, Harvard Uni- 
versity, ABL, Nov. 22, 1944. 

Div. 15-124-M2 

Broad-Band DF System, J. V. Granger, Report 1045-12, 
Project RP-982, OSRD Liaison Office WA-4390-lla, 
Harvard University, ABL, Apr. 23, 1945. 

Div. 15-313.2-M2 

Modifications to Jackal AN /ART-3 {XA-1), J. W. 
Keuffel, 1045-TM-l, OSRD Liaison Office WA-3045-3. 
Harvard University, ABL, Sept. 7, 1944. 

Div. 15-401. 2-M3 

Jamming Trials of Jackal AN / ART-3 {XA-1), D. K. 
Reynolds, 1045-TM-2, Harvard University, ABL, Sept. 
21, 1944. Div. 15-401. 2-M4 

Jostle IV Field Tests, Richard C. King, 1045-TM-3, 
Project RP-986, OSRD Liaison Office WA-3969-10A, 
Harvard University, ABL, Feb. 23, 1945. 

Div. 15-401.21-Ml 
Modifications to Carpet I {AN / APT-2), Carpet III 
{AN/APQ-9), and Rug {AN/ APQ-2) Transmitters for 


496 


BIBLIOGRAPHY 


869. 


Spot- Frequency Jamming, J. Gregg Stephenson, 1045- 
TM-4, Project RP-997, OSRD Liaison Office WA- 
4143-1, Harvard University, ABL, Feb. 27, 1945. 

Div. 15-322. 124-M8 
Installation of Anti- Jamming Devices in the German 
Ground Radar Equipment FuSE 62, Lee B. Lusted, 
1045-TM-5, Project RP-998, OSRD Liaison Office WA- 
4236-2, Harvard University, ABL, Mar. 21, 1945. 

Div. 15-711.2-Ml 


870. Modification Kit for AS-69 / APT (M-2202) Antenna for 
Operation 450-500 Me Band, G. H. Klemm, 1045-TM-6, 
Project RP-303, OSRD Liaison Office WA-4363-1, Har- 
vard University, ABL, Apr. 19, 1945. 

Div. 15-332.11-M4 

871. Availability of D-C Power for ROM in B-17 and B-24 

Aircraft, Milton B. Adams, 1045-TM-7, Project RP-987, 
OSRD Liaison Office WA-4446-13B, Harvard Univer- 
sity, ABL, May 7, 1945. Div. 15-322. 15-M4 


OSRD APPOINTEES 


DIVISION 15 


Chief 

C. G. Suits 

Officers 

J. H. Moore, Deputy Chief 
H. M. Johnson, Special Assistant to the Chief 


Technical Aides 


H. W. Albrecht 
D. B. Harris 


H. D. Harris 
J. F. McClean 


Administrative Assistant 

T. A. Hatch 


Members 


K. C. Black 

L. A. DuBridge 
G. W. Gilman 
D. G. C. Hare 


L. N. Ridenour (Alternate) 
F. E. Terman 


C. B. JOLLIFFE 
H. K. Potter 


Consultants 


A. B. Clark 
A. W. Hull 
R. W. Larson 


H. H. Beverage 
R. Bown 
H. A. Chinn 


Frank Lewis 


CONTRACT XUISIBERS. CONTRACTORS. AND SUBJECT OF CONTRACTS 


Contract 

Number 

Name and Address 
of Contractor 

Subject 

OEMsr-63 

General Radio Company 

30 State Street 

Cambridge, Massachusetts 

Development of the SCR-587 (ARC-1) search receiver. 

OEMsr-89 

Farnsworth Television & Radio Corporation 

Fort Wayne, Indiana 

Radio interference generator. 

NDCrc-100 

Ohio State University Research Foundation 
Columbus 10, Ohio 

Antenna patterns for aircraft. 

OEMsr-285 

International Telephone & Radio Manufacturing 
Corporation 

67 Broad Street 

New York, New York 

Radio interference generator. 

OEMsr-411 

Radio Research Laboratory, Harvard University 
Cambridge, Massachusetts 

Operation of a central laboratory for RCM research and 
development. 

OEMsr-626 

Bell Telephone Laboratories (through Western 
Electric Company) 

463 West Street 

New York 14, New York 

Study of interference generation. 

OEMsr-653 

Columbia Broadcasting System 

485 Madison Avenue 

New York 22, New York 

The development of a listening through radar counter- 
measures system and construction of model thereof. 

OEMsr-747 

Westinghouse Electric Corporation, Research 
Laboratories 

East Pittsburgh, Pennsylvania 

Design, development, fabrication, and testing of resnatron 
tubes. 

OEMsr-759 

Ohio State University Research Foundation 
Columbus 10, Ohio 

Radiation characteristics of airborne antennas. 

OEMsr-778 

Bell Telephone Laboratories (through Western 
Electric Company) 

463 West Street 

New York 14, New York 

Study of radio jamming. 

OEMsr-806 

Galvin Manufacturing Corporation 

4545 Augusta Blvd. 

Chicago, Illinois 

A contract for the transition and procurement of a limited 
number of units of the RRL-CllOO (AN/APR-2) search 
receiver. 

OEMsr-807 

Delco Radio Division, General Motors Corpora- 
tion 

Kokomo, Indiana 

Emergency transition contract intended to assist in the 
procurement of Division 15 developments. No activity 
occurred under this contract. 

OEMsr-808 

Galvin Manufacturing Corporation 

4545 Augusta Blvd. 

Chicago, Illinois 

Emergency transition contract intended to assist in the 
procurement of Division 15 developments. No activity 
occurred under this contract. 

OEMsr-867 

Columbia Broadcasting System 

485 Madison Avenue 

New York 22, New York 

Research, development and the construction of special 
radio apparatus in the field of radio countermeasures. 

OEMsr-895 

RCA Victor Division of Radio Corporation of 
America 

66 Broad Street 

New York, New York 

Radio countermeasures research and development. 

OEMsr-923 

General Radio Company 

30 State Street 

Cambridge, Massachusetts 

The development of special test oscillators and signal 
generators. 

OEMsr-931 

General Electric Company, Research Laboratory 
Schenectady, New York 

Research on radio and radar countermeasures. 

OEMsr-936 

Federal Telephone & Radio Corporation 

67 Broad Street 

New York, New York 

Study of jamming and anti-jamming of radio telegraphy. 

OEMsr-937 

Federal Telephone & Radio Corporation 

67 Broad Street 

New York. New York ^ 

A radio communication system protected against inter- 
ference. 


498 



CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS (Continued) 


Contract 

Number 

Name and Address 
of Contractor 

Subject 

1 

OEMsr-940 

Bell Telephone Laboratories (through Western 
Electric Company) 

463 West Street 

New York, New York 

1 

Radio barrage jamming and anti-jamming studies. 

OEMsr-966 

Bell Telephone Laboratories (through Western 
Electric Company) 

463 West Street 

New York, New York 

Study of radio jamming and anti-jamming. 

OEMsr-993 

Bell Telephone Laboratories (through Western 
Electric Company) 

180 Varick Street 

New York 14, New York 

Scanning reception in radio countermeasures. 

OEMsr-1005 

General Radio Company 

30 State Street 

Cambridge, Massachusetts 

Development of special signal generators for receiver 
vulnerability tests at the Jansky and Bailey laboratory. 

OEMsr-1019 

General Electric Company, Research Laboratory 
Schenectady, New York 

Studies and experimental investigations in connection with 
development and testing of a line of tunable magnetrons 
to cover frequency of 500 to 30,000 Me. 

OEMsr-1024 

Jansky and Bailey 

1222 Wisconsin Avenue 

Washington 7, D, C. 

Susceptibility tests on communications receivers. 

OEMsr-1034 

Federal Telephone & Radio Corporation 

67 Broad Street 

New York, New York 

New L-band transmitter tubes. 

OEMsr-1043 

RCA Victor Division of Radio Corporation of 
America 

Lancaster, Pennsylvania 

Model shop facilities and research and development of CW 
magnetron tubes. 

OEMsr-1045 

Radio Research Laboratory, Harvard University 
Cambridge, Massachusetts 

The operation of an RCM laboratory in Great Britain. 

OEMsr-1060 

RCA Victor Division of Radio Corporation of 
America 

Lancaster, Pennsylvania 

Investigation and development of electronic noise sources. 

OEMsr-1107 

Westinghouse Electric Corporation, Research 
Laboratories 

East Pittsburgh, Pennsylvania 

High power ground communications jammer. 

OEMsr-1138 

Panoramic Radio Corporation 

245 West 55th Street 

New York, New York 

Electronic tuning for panoramic reception. 

OEMsr-1176 

Ballantine Laboratories 

1 Fanny Road 

Boonton, New York 

Research on fundamental processes for production and 
development of noise by various sources. 

OEMsr-1179 

Midwest Radio Corporation 

909 Broadway 

Cincinnati, Ohio 

Prototype model production (Pad). 

OEMsr-1222 

Bell Telephone Laboratories (through Western 
Electric Company) 

463 West Street 

New York 14, New York 

Vacuum tube research and development. 

OEMsr-1232 

Delta Star Electric Company 

2437 Fulton Street 

Chicago 12, Illinois 

Engineering and development of two models of the RRL 
A-500C (Tuba) equipment for the British under lend- 
lease requisition. 

OEMsr-1275 

Federal Telephone & Radio Corporation 

67 Broad Street 

New York, New York 

500 Watt amplifiers for AN/ARQ-10. 


499 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS {Coiitinued) 


Contract 

Number 

Name and Address 
of Contractor 

Subject 

OEMsr-1302 

Ring &. Clark 

Munsey Building 

Washington, D. C. 

Consulting services on radio countermeasures. 

OEMsr-1305 

Airborne Instruments Laboratories (under the 
auspices of Columbia University) 

160 Old Country Road 

Mineola, New York 

Research and development on radio, radar, guided missiles 
countermeasures, and counter-counter measures. 

OEMsr-1309 

Westinghouse Electric Corporation 

5901 Breakwater Avenue 

Cleveland, Ohio 

Development and production of 6-20 kw transportable 
communications jammers — 30-50 Me — frequency modu- 
lated over 4 Me band at 240 cps. 

OEMsr-1310 

W’^estinghouse Electric Corporation 

5901 Breakwater Avenue 

Cleveland, Ohio 

Production of 10-20 kw transportable communications 
jammers — 30-50 Me — frequency modulated over 4 Me 
band at 240 c. 

OEMsr-1324 

International Diesel Electric Company, Inc. 

36-50 38th Street 

Long Island City, New York 

Power supply units for 20 kw communication ground 
jammers (Cigar). 

OEMsr-1328 

Maryland Engineering Company 

Pikesville, Maryland 

Development and production of 18 rhombic antenna assem- 
blies for use with AN/MRT-l. 

OEMsr-1357 

Litton Engineering Company 

P. 0. Box 749 

Redwood City, California 

Development and supply of electron tube models. 

OEMsr-1428 

Erco Radio Laboratories 

231 Main Street 

Hempstead, New York 

CW spot jammer (Stopwatch). 

OEMsr-1430 

Federal Telephone & Radio Corporation 

67 Broad Street 

New York 4, New York 

Development and supply of electron tube models. 

OEMsr-1456 

Sylvania Electric Products 

60 Boston Street 

Salem, Massachusetts 

Development and supply of electron tube models. 

OEMsr-1458 

Federal Telephone & Radio Corporation 

67 Broad Street 

New York 4, New York 

Direction finders and D-F countermeasures. 


500 


SERVICE PROJECT NUMBERS 

The projects listed below were transmitted to the Office of the Executive Secretary, OSRD, from 
the War or Navy Department through either the War Department Liaison Officer for NDRC or the 
Office of Research and Inventions (formerly the Coordinator of Research and Development), Navy 
Department. They were assigned Division 15 RP numbers as indicated. Reference to pages 511-518 
will provide information as to the Division 15 contractor to whom each project was assigned. 


Service 

Project 

Number Subject RP No. 


AC-69 

AC-71 


AC-290 

AC-290.12 

AC-290.13 

AC-290.14 

AC-290.15 


AC-290.16 


AC-290.17 


AC-290.18 

AC-291 

AC-291.01 


AC-292 

AC-292.01 


AC-292.03 


AC-293 

AC-293.01 


ARMY AIR FORCES PROJECT NUMBERS 

Chaff cutters 

Development of Chaff (Window) dispenser 

Ext. of: Jettison type Chaff dispenser for fighter aircraft 

Ext. of: Consultant service (AAF) on development and improvement of Chaff 
dispensers 

Radar search and analysis 

Research and development of airborne single dial search receivers with image re- 
sponse and spurious responses from all sources reduced to a minimum and op- 
erating from 1,000 to 12,000 Me 

Research and development of airborne single dial search receivers with image re- 
sponse and spurious responses from all sources reduced to a minimum and op- 
erating from 11,000 to 33,000 Me 

Research and development of necessary antenna systems for equipment developed 
under Project AC-290 

Research and development of the necessary adapters, analyzers, recorders, and 
other auxiliary equipment for use with receivers developed under AC-290 and 
the assembly of various receivers and auxiliary devices into smoothly working 
systems 

Investigation and development of improvements for existing airborne search re- 
ceivers and making recommendations thereon to the air technical service com- 
mand 

Study of the radar RCM search problem above 1,000 Me with a view toward 
recommending improvements in e.xisting radar Ferret aircraft installations and 
planning for future Ferrets 

Research and development of necessary search receiving systems for use in deter- 
mining the extent of the enemy’s employment of radio types of proximity fuses 

Communications intercept and analysis 

Study of the communication, navigation and special radio RCM search problems 
with a view toward recommending improvements in existing communication 
Ferret aircraft installations and planning for future Ferrets 

Radar AJ and AJ training 

General study of means of reducing the effect of all types of enemy offensive coun- 
termeasures 

Study of vulnerability of selected airborne radar sets and making recommenda- 
tions for operating procedure to combat jamming or reflection devices and for 
changes that can be made to improve performance 

Communications AJ and AJ training 

Study of vulnerability of selected airborne radio sets and making recommenda- 
tions for changes that can be made to improve performance in the presence of 
intentional interference 


AC-293.04 Research and development of protected airborne communications systems 
AC-293.05 Studies of J and AJ of radio telegraphy 


R P-1 03a 
RP-406b 
RP-406b 
RP-273 

RP-408a, b. c 
RP-286a, c 
RP-435a, b, c 
RP-442b 
RP-472 
RP-286 


RP-107C 
RP-138d, f 
RP-425a, b 
RP-447 


RP-286C 

RP-442b 

RP-443 

RP-448 

RP-315 


RP-117a, d 


RP-298d 
RP-440a, b 


RP-214 

RP-318 

RP-406a 

RP-367 

RP-368 

RP-452 

RP-189 

RP-192 

RP-463 

RP-464 

RP-465 

RP-466 

RP-467 

RP-124 

RP-109a 


501 


SERVICE PROJECT NUMBERS {Continued) 


Service 

Project 

Number Subject RP No. 


ARMY AIR FORCES PROJECT NUMBERS {Continued) 

AC-294 Radar jamming 

AC-294.12 Development of AN/APT-4 (165-780 Me) 

AC-294.13 Development of AN/APT-8 (700 to 1200 Me) 

AC-294.17 Researeh and development of neeessary antenna systems for equipment developed 
under Projeet AC-294 


AC-294.18 Development of tuning adapter AN/APA-27 

AC-294.20 Researeh and development of airborne radar jamming systems for frequeney range 
1,000 to 5,500 Me 


Ext. No. 1 — Consultant serviee on AN/APQ-20 
AC-294.22 Propagation studies in radar jamming 

AC-294.23 Researeh and development of low-powered (25-50 watts) tunable oseillators eapa- 
ble of being modulated by noise over a reasonably wide band and eovering the 
frequeney range 390-11,000 Me 


AC-294.27 Researeh and development of airborne radar jamming systems for frequeney range 
5,000 to 11,000 Me 


AC-294.28 


AC-294.29 

AC-295 

AC-295.06 

AC-295.07 

AC-295.10 

AC-296 

AC-296.01 


Investigation and development of improvements for existing airborne radar jam- 
mers and making reeommendations thereon to the Air Teehnieal Serviee Com- 
mand 

Researeh and development of neeessary airborne jamming systems for use against 
radio types of enemy proximity fuses 

Communieations jamming 

Researeh and development of neeessary antenna systems for eommunieations 
jamming equipment 

Development of RF amplifier 500 watts (14-60 Me) 

Study of eommunieation jamming program and eondueting of eommunieations 
jamming effeetiveness tests 

Deeeption deviees 

Researeh and development of deeeption deviees (Chaff, Rope, Kites, ete.) from 30 
to 33,000 Me 


Ext. No. 1 — Misdireeting lobed radar by meehanieal means 
AC-296.04 Research and development of identifieation type Chaff for the S and X bands for 
use in ground veetoring of elose support aireraft and in identifieation of single 
friendly aireraft for landing purposes 
AC-297 Direetion finder and speeial developments 

AC-297.04 Researeh and development of airborne direetion finding assembly AN/ARA-5 
(1.75 to 30 Me) 


AC-297.06 Researeh and development of airborne direetion finding assembly (30-100 Me) 

AC-297.07 Investigation and development of improvements for existing airborne direetion 
finding assemblies and making reeommendations thereon to the Air Teehnieal 
Serviee Command 


RP-285 

RP-338a 

RP-338 

RP-244a 

RP-338 

RP-138d, e, f 

RP-260a to d 

RP-303a, e, d, f, g, h 

RP-352 

RP-380 

RP-169a, b, e 

RP-295a 

RP-424a, b 

RP-425a, b 

RP-428 

RP-435a, b 

RP-454 

RP-455 

RP-456 

RP-472 

RP-284 

RP-299a 

RP-169b 

RP-244b 

RP-295a 

RP-418 

RP-430a, b, c 

RP-221 

RP-286a 

R P-403 

RP-435a 

RP-338a, b 


RP-117a, b, d 


RP-137 
RP-260a to d 
RP-272a, b 
RP-109a 
R P-441 

RP-103a 

RP-257 

RP-258b 

RP-406b, e, d, e, f 

RP-406e 

RP-103a 


RP-298a 

RP-404 

RP-437 

RP-444 

RP-298d 

RP-444 

RP-298a 


502 


SERVICE PROJECT NUMBERS {Continued) 


Service 

Project 

Number Subject / RP No. 


ARMY AIR FORCES PROJECT NUMBERS {Continued) 


AC-298 Special countermeasures service 

AC-298.04 NDRC consultation and advisor service on airborne RCM procurement RP-284 

RP-314 

RP-333 

RP-431 

AC-298.05 Ferret antennas and tests (radar and communications) RP-315 

RP-440a 

AC-298.10 NDRC assistance in preparation of RCM (including AJ) training literature, train- RP-317a 

ing films, and actual training of selected RCM personnel RP-471 

AC-298.11 Consultant service on radar tow targets RP-349 

AC-299 RCM test equipment 

AC-299.06 Research and development of special test equipment required for airborne radar RP-392 

jamming systems covering 1,000 to 11,000 Me RP-479 

AC-299.07 Research and development of special test equipment required for airborne micro- RP-306c, d 

wave search receivers covering 1,000 to 33,000 Me RP-416a 

RP-468 
R P-469 
RP-476 

AC-300 NDRC consultation on airborne, RCM installations RP-341 

AC-300.02 Communication Ferret C-1. RP-440a 


ARMY-NAVY PROJECT NUMBERS 

RP-269 
RP-317a 


AN-8 Study of effective echoing areas of aircraft 

AN- 17 Training films for anti-jamming 


NA VY PROJECT NUMBERS 

NA-102 Radar countermeasures (RCM program Division 15 — general) 

NA-109 Jamming and anti-jamming radio controlled aircraft 


NA-151 PB4Y-2 aircraft countermeasures equipment installation 
NA-156 X-band radar jammer and intercept receiver 


NA-157 Radar search receivers and homing antennas 

NA-159 Incorporation of anti-jamming devices in radar equipment 


RP-394 

RP-430a 

RP-117a, b, d 

RP-278 

RP-359 

RP-360 

RP-361 

RP-362 

RP-363 

RP-382 

RP-383 

RP-384 

RP-388 

RP-389 

RP-242 

RP-158a 

RP-221 

RP-286a 

RP-403 

RP-435a 

RP-302 

RP-172 

RP-223 

RP-224 

RP-225 

RP-324 

RP-411 

RP-412 

RP-413 


♦ 


503 


SERVICE PROJECT NUMBERS {Continued) 


Service 

Project 

Number Subject RP No. 


NA-180 


NA-185 


NA-187 


NA-189 


NA-199 

NA-204 

NA-209 

NA-212 


NA-213 

NA-215 

NA-217 

NA-218 


NA.219 

NA-220 

NA-221 

NA-224 

NA-230 

NA-234 


NA-237 
NO- 193 


NO-217 

NO-218 

NO-219 


NO-239 


NO-273 

NO-278 

NO-287 

NP-2 

NR-112 


NAVY PROJECT NUMBERS {Continued) 


To determine the possibility of identifying radar echoes from corner reflectors as RP-258a 
contrasted to echoes from military targets RP-406j 

Ext. of: Production of 500 Angels for operational tests RP-258a 

Study and improvement of anti-jamming features of radar systems AN/APS-3, RP-225 
AN/APS-4, AN/APS-6, AN/APS-15, and AN-APS-1 RP-411 

RP-412 

RP-413 

Development of airborne jamming transmitters to cover range from 175 to 1200 RP-244a 

Me RP-285 

RP-338 

Development of airborne S-band jammer RP-169b 


RP-286C 

RP-295a 

RP-303C 

RP-414 

RP-418 

RP-424a. b 

RP-425a, b 

RP-435a, b 

RP-454 

RP-455 

RP-472 


Assistance on antenna problems involving radio and radar equipment for P4M RP-137 
aircraft 

Consulting services on CU-43/APT & CU-44/APT Baiuns RP-273 

Development of stub antennas for use on high speed aircraft RP-303e 

Development of faired-in antennas for naval aircraft RP-260a, c, d 

RP-303f, i 
R P-484 

Determination of radiation patterns of naval aircraft RP-137 

Consulting services on radar training set AN/TPQ-T2 RP-273 

Electronic test equipment developments— 4,000-33,000 Me RP-446 

Anti-jamming of airborne radar equipment RP-2 14a 

RP-324 

Anti-jamming study of AN/APS-4 radar equipment RP-411 

Anti-jamming study of AN/APA-16 radar bombsight RP-449 

Antenna patterns on SB2C and PB4Y-2 aircraft RP-137 

Airborne jamming system for use with AN/APT-5 transmitter RP-459 

Study of CM devices against proximity fuzes ' RP-117a 

Airborne RCM operator’s manual RP-338b 

RP-477 

Consulting services on SA-44A/APR switch RP-273 

Development of a jamming simulator for radar trainer Mark 1 RP-313 

Ext. of: Consultant service (BuShips) on manufacture of E1300 interference RP-273 
generator 

Investigation of vulnerability of Pelican receiver to jamming RP-355 

Training jammers for the radar equipment Mark 4 and Mark 12 RP-273 

RP-364a 

Assistance to Navy on countermeasures training film-fire control radars, Mark 3 RP-3l7a 
and Mark 4 

Development of model of the Video filter for anti-jamming device for radar equip- RP-2 14 
ment Mark 4 RP-273 

Determination of vulnerability of Mark 31 radar system to countermeasures RP-436 

Photographs illustrating anti-jamming of radar RP-3l7b 

Consulting service on applying doppler to radar equipment Mark 4 RP-406 

Radar anti-jamming training course RP-387 

Consulting services on analysis of enemy electronic devices RP-478 


504 


SERVICE PROJECT NUMBERS {Continued) 


Service 

Project 

Number Subject RP No. 


NS-128 


NS- 179 
NS- 189 
NS-193 
NS-200 

NS-202 


NS-203 

NS-204 


NS-206 

NS-208 

NS-209 

NS-213 

NS-214 

NS-215 

NS-216 

NS-217 

NS-218 

NS-219 


NS-220 

NS-241 


NA VY PROJECT NUMBERS {Continued)^ 

Development of means for jamming radio communication circuits RP-109 

RP-109a 

RP-115 

RP-122 

RP-148 

RP-149 

RP-150 

RP-151 

RP-152 

RP-153 

RP-154 

RP-155 

RP-199 

RP-200 

RP-232 

RP-233 

RP-234 

RP-259 

RP-260a, b, c 

RP-261b 

RP-307 

RP-325 

RP-358 

RP-451 


Countermeasures— direction finder deception RP-252 

Consultant service (Navy) for AN/APR- 1, 2, 5, and 6 RP-273 

Recording mechanism for AN/APR-1 search receiver RP-276 

Expendable jamming equipment RP-132 

RP-237 

Direction finding systems R P-209 

RP-271a to f 
RP-298a to f 

Development of monitoring and tracking indicator RP-263 

Shipborne radar jamming RP-138c 


RP-247 

RP-275 

RP-279 

RP-305 

RP-344 

RP-394 


Jamming transmitter using Type ZP579 magnetron (consultant service) RP-244a 

RP-316 

Consulting service on Type ZP579 magnetron RP-244a 

Development of a practice jammer for low-frequency navy radar RP-323 

Jamming of radio altimeters RP-334 

Consulting service on shipborne radar jamming transmitter being developed by RP-244a 
General Electric Company RP-335 

Development of antenna for use with ZP-590 magnetron jamming transmitter RP-138 

Modulator for jamming transmitters, general application for training RP-348 

General Electric Company CW magnetron ZP590 RP-244a 

General Electric Company CW magnetron ZP-584 RP-244a 

Airborne transmitter development project (using 150- watt magnetron tubes) RP-244a 

RP-285 

RP-338 

Consulting services on directional interceptor antennas for submarines RP-138b 

RP-354 

Anti-jamming methods for shipborne radar RP-214 

RP-357 


505 


SERVICE PROJECT NUMBERS {Continued) 


Service 

Project 

Number 

Subject 

RP No. 

NS-244 

NAVY PROJECT NUMBERS {Continued) 

Consulting serviees of the Radio Researeh Laboratory to the Aviola Radio Cor- 

RP-298e 

NS-251 

poration, Glendale, California 

Radar eountermeasures equipments (Peter) 

RP-156 

NS-254 

Consultant serviees on high-power jam transmitter for RCM applieation 

RP-321 

NS-258 

Reduetion of radar interferenee to eommunieations systems 

RP-189 

NS-259 

Consulting serviee on RRL Projeet M3000 

RP-298e 

NS-260 

Dinamate equipment for operational tests in eonneetion with CM against guided 

RP-250 

NS-261 

missiles 

Redesign of the M3000 direetion finder 

RP-267 

R P-303 

RP-271b 

NS-264 

Type G1107 double tape window dispensers 

RP-273 

RP-406b 

NS-266 

Model shop proeurement of the M2600 direetion finder 

RP-27lb 

NS-278 

Development of jammer tubes and eireuits 

RP-116 

NS-289 

Development of MAS type jamming equipment 

RP-159a, b 

RP-295d 

RP-321 

RP-351 

R P-391 

RP-4l7b 

RP-395 

NS-290 

Consulting serviee on produetion of TS-109/SPR equipment 

RP-273 

NS-310 

Development of 25 eight-way switehes to be used with model TEA jamming equip- 

RP-402a 

NS-311 

ment for GMCM use 

Development of jamming transmitter on S-band 

RP-158a 

NS-312 

Ext. of: Consultant serviee in eonneetion with produetion of AN/APQ-20 trans- 
mitter 

Development of airborne system for homing on enemy airborne radar 

RP-169 

RP-405 

RP-415 

RP-417a, b 

RP-273 

RP-209 

NS-313 

Development of M3000 and M2300 antenna heads 

RP-271d 

NS-318 

D2100 mierowave reeeivers 

RP-408a, b 

NS-328 

Ext. of: Consulting serviee in eonneetion with modifieation of 25 AN/SPR-7A 
equipments 

Study of antenna patterns of ship models 

RP-273 

RP-261b 


NS-333 

NS-340 

NS-345 

NS-348 

NS-393.05 

NS-394.01 


NS-394.02 


NS.394.03 


Type M2900 antenna series in ranges 80-190 Me and 750-1300 Me 
Modifieation of AN/APT-4 eountermeasures equipment 
Modifieation of frequeney range of U700, jamming signal generator 
Consultant serviees on model DBM direetion finding equipment 
Study of vulnerability of Navy FM equipment to jamming and development of 
anti-jamming measures 

Development of low-power (up to 150 watts) vaeuum tubes in the frequeney range 
60 to 12,000 Me and eonsulting serviee as requested by BuShips 


Development of medium-power (150-1500 watts) vaeuum tubes in the frequeney 
range 60 to 12,000 Me and eonsulting serviee as requested by BuShips 


Development of high-power (above 1500 watts) vaeuum tubes in the frequeney 
range 60 to 12,000 Me and eonsulting serviee as requested by BuShips 


RP-427 

RP-138C 

RP-338 

RP-364a 

RP-273 

RP-334 

RP-244a, b 

RP-332 

RP-393 

RP-418 

RP-430a, b 

R P-434 

RP-439 

RP-158a, b, e, d, f 

RP-244a 

RP-247 

RP-434 

RP-116 

RP-247 

R P-351 

RP-434 


506 


SERVICE PROJECT NUMBERS {Continued) 


Service 

Project 

Number 

Subject 

RP No. 

NS-394.04 

NAVY PROJECT NUMBERS {Continued) 

Design data and consulting service on modification of TDY transmitter to use 

RP-138e 


QK-44 in frequency 2590-3430 Me and antenna design 

RP-303C 

NS-394.10 

S-band jamming system— -Range: 2700-3300 Me (2400-4000 Me) 

RP-158a, b 

NS-394.14 

General research on RCM antennas 

RP-303j, k 

RP-426 

RP-435 

R P-442 

RP-457 

RP-461a to c 
RP-462a, b 

RP-138C 

NS-394.17 

Construction of thirty (30) eight-way RE switches for use with the TDY system 

RP-402a 

NS-394.18 

similar to those developed for the TEA equipment 

S-band antenna for countermeasures purposes 

RP-303b 

NS-394.19 

Development of shipboard antennas for X-band countermeasures systems 

RP-303 

NS-394.20 

Development of antenna for TDY countermeasures systems 

RP-138C 

NS-394.21 

Antenna for AN/CPT-3 Coyote Buoy 

RP-303e 

NS-395.04 

Jamming equipment for multiple signals of simultaneous occurrence 

RP-389 

NS-396.04 

Consulting services on S-band Window for rockets 

RP-273 

NS-397.03 

Development of a low-frequency antenna head for the AN/APA-17 direction 

RP-298d 

NS-397.07 

finder 

Development of antenna head for model DBM-1 direction finding equipment for 

RP-271d, e 


frequency range from 3000-12,000 Me 

RP-298f 

NS-397.08 

Development of a radio-AN/APA-17 antenna head for range of 1000-4500 Me 

RP-271d 


Ext. of: Consultant service to BuShips in connection with production of M4500 

RP-379 

NS-397.10 

antenna by Aviola Radio Corporation 

AN/APA-48 direction finder equipments 

RP-209 

NS-398.07 

Development of AN/ARQ-11 countermeasures equipment 

RP-419b 

NS-399.05 

Radar CM manual Radseven 

RP-421 

RP-480 


SC-90 

SIGNAL CORPS PROJECT NUMBERS 

Radar search and warning receivers 


SC-90.01 

Zero catcher I — RC-164 B 

RP-147 

SC-90.02 

Automatic search receiver — AN/APR-2 

RP-139 

SC-90.03 

Tuning unit for SCR-587 — TU-56A 

RP-141 

SC-90.04 

Tuning unit for SCR-587— TU-58B 

RP-141 

SC-90.05 

Tuning unit for SCR-587— TU-57B 

RP-141 

SC-90.06 

Tuning unit for SCR-587 — TU-59A 

RP-141 

SC-90.07 

Unit construction receiver — AN/APR-4 

RP-144 

SC-90.08 

Microwave search receiver — AN/APR-5 

RP-212 

RP-135 

SC-90.09 

Microwave search receiver — AN/APR-6 

RP-291 

SC-90.10 

Warning receiver — AN/APR-3 

RP-287 

SC-90.11 

Development of recording assembly AN/APA-23 

RP-276 

SC-92 

Radar anti-jamming and anti-jamming training equipment 


SC-92.01 

Study of radar anti-jamming circuits 

RP-214 

SC-92.02 

Anti-jamming for AN/APS-3 

RP-225 

SC-92.03 

Anti-jamming for selected airborne radar sets 

RP-277 

SC-92.04 

ASV jamming filter (SCR-521) 

RP-367 

RP-368 

RP-222 

SC-92.05 

Development of trainer equipment AN/TPQ-T2 

RP-160 

SC-92.06 

Development of microwave training generator A 1700 

RP-191 

SC-92.07 

Development of anti-jamming for SCR-268 

RP-171 


507 


SERVICE PROJECT NUMBERS {Continued) 


Service 



Project 

Number 

Subject 

RP No. 


SIGNAL CORPS PROJECT NUMBERS {Continued) 


SC-92.08 

Integration methods for indicators 

RP-318 

SC.92.09 

Development of training generator AN/UPT-Tl 

RP-180 

SC-92.10 

Radar anti-jamming training film 

RP-317a 

SC-92.11 

Vulnerability study of radio set AN/TPL-1 with respect to electronic and window 

RP-453 


jamming 


SC-92.12 

Vulnerability study of radio set SCR-545 with respect to electronic jamming 

RP-475 

SC-93 

Communications anti-jamming and anti-jamming training equipment 


SC. 93.01 

Receiver vulnerability investigation 

RP-189 

RP-192 

RP-397 

RP-463 

R P-464 

RP-465 

RP-466 

RP-467 

SC-93.02 

Pulse communications jamming and anti-jamming studies 

RP-123 

RP-460 

SC-93.03 

Study of anti-jamming possibilities of super audible pulse 

RP-229 

SC-93.04 

Research and development of protected communication system 

RP-124 

SC-93.05 

Studies of jamming and anti-jamming of radio telegraphy 

RP-109a 

RP-159 

SC-93.06 

Studies of AM vs. FM from anti-jamming standpoint 

RP-131 

SC-94 

Radar jamming 

RP-447 

SC-94.01 

Mandrel AN/APT-3 

RP-163 

SC-94.02 

Dina AN/APT-1 

RP-309 

SC-94.03 

Power amplifier for AN/APT-1 and AN/APT-3 (AN/AM-14/APT) 

RP-218 

SC-94.04 

Power amplifier for AN/APT-1 (AN/AM-18/APT) 

RP-329 

SC-94.05 

Rug AN/APQ-2 

RP-164 

SC-94.06 

Carpet AN/APT-2 

RP-165 

SC-94.07 

High-power Carpet AN/APQ-9 

RP-166 

RP-166a 

SC-94.08 

Carpet Sweeper AN/APQ-1 

RP-167 

SC-94.09 

Carpet IV AN/APT-5 

RP-336 

SC-94.11 

Maggie AN/APT-7 (90 to 400) 

RP-285 

RP-338 

SC-94.12 

Maggie AN/APT-4 (310 to 750) 

RP-244a 

RP-285 

RP-338 

SC-94.13 

Maggie AN/APT-8 (600 to 1000) 

RP-244a 

RP-285 

RP-338 

SC-94.14 

Mobile jammer for AN/MPQ-1 

RP-lOO 

SC-94.15 

Special antenna development 

RP-138 

SC-94.16 

Research and development of electronic noise sources 

RP-181 

RP-187a, b 

RP-196 

RP-311 

SC-94.17 

Research and development of antennas for use with jammers developed under 

RP-107a 


SC-94 

RP-138 

RP-260a, b, c 

RP-345 

RP-352 

SC-94.18 

Lock-on jamming attachment for AN/APT-4 and AN/APQ-2 

RP-380 

SC-94.19 

Development of a ground based mobile barrage jamming transmitter using a 

RP-116 


tunable magnetron 

RP-321 

RP-340 

RP-351 


508 


SERVICE PROJECT NUMBERS {Continued) 


Service 

Project 

Number Subject RP No. 


SC-94.20 

SC-94.21 

SC-94.22 

SC-94.23 

SC-94.24 

SC-94.25 


SC-95 

SC-95.01 

SC-95.02 

SC-95.03 

SC-95.04 

SC-95.05 

SC-95.06 


SC-95.07 

SC-95.08 

SC-95.09 

SC-95.10 


SC-95.11 

SC-95.12 

SC-95.13 

SC-95.14 

SC-95.16 

SC-96 

SC-96.01 


SC-96.02 

SC-96.03 

SC-96.04 


SIGNAL CORPS PROJECT NUMBERS {Continued) 

Development of radar jamming set AN/APT-9 (1000-2200 Me) 


Development of radar jamming equipment (2000-3500 Me) 


Propagation studies in radar jamming 

Researeh and development of low-powered (25-50 watt) tunable oseillators (390- 
11,000 Me) 


Development of a 10 kw tunable magnetron (and transmitter eireuit work) 

Development of a ground-based radar jamming equipment using 1-kw tunable 
magnetrons (200-4000 Me) 


Communieations jamming 
Development of FM jammer (Jaekal II) 

Dinamate AN/ARQ-8 

Development and proeurement of Cigar AN/MRT-1 
Chiek AN/CRT-2 
Wave propagation study 

Researeh and development of broad-band antenna for eommunieations jamming 
equipment 

Development of radio frequeney amplifier AM-33/ART 
Development of radio frequeney amplifier 500 watts (14-60 Me) 

Airborne spot jammer system study 
Communieations jamming effeetiveness tests 


Development of listening through and jammer alignment system 
Development of 50 kw radio jamming system (20-70 Me) (AN/GRQ-1) 
Modifieation kit for radio set AN/MRT-1 
Researeh and development of radio set AN/ARQ-11 

Countermeasures against radio navigational aids 

Deeeption deviees 

Diffuse eonfusion refleetors (Window) 


Researeh and development of eorner refleetors (Angels) 
Window filler for mortar shell 
Simulation of radio powered VT fuses 


RP-169 

RP-204 

RP-407 

RP-425a, b 

RP-428 

RP-430a 

RP-407 

RP-414 

RP-424 

RP-425a, b 

RP-430a 

RP-299a, b 

RP-169b 

RP-244b 

RP-295a 

RP-418 

RP-430a, b, e 

RP-116b 

RP-321 

RP-351 

RP-158a, b, e, d, f 
RP-303j, k 
RP-405 
RP-417a, b 
R P-442 
RP-457 
RP-461a, b, e 
RP-462a, b 

RP-150 

RP-250 

RP-267 

RP-356a, b 

RP-132 

RP-149 

RP-137 

RP-259 

RP-260a 

RP-344 

RP-272a, b 

RP-358 

RP-109 

R P-1 09a 

RP-451 

RP-122 

RP-420a, b 

RP-356e 

RP-419a 

RP-421 

RP-422 

RP-445 

RP-103a 

RP-257 

RP-406b, e, d, e, f, g 
RP-258b 
RP-103b 
RP-117a 


509 


SERVICE PROJECT NUMBERS (Continued) 


Sendee 

Project 

Number 

Subject 

RP No. 


SIGNAL CORPS PROJECT NUMBERS (Continued) 


SC-97 

Direction finders and special developments 


SC-97.01 

Homing and direction finding AN/APQ-14 

RP-188 

SC-97.02 

Direction finding antenna AN/APA-24 (100-480 Me) 

RP-298a 

SC-97.03 

Direction finding system for 250 to 800 Me (AN/APA-17) 

RP-298 

SC-97.04 

Research and development of airborne direction finding antenna AN/ARA-5 

RP-404 


(1.75-30 Me) 

RP-437 



R P-444 

SC-97.05 

Research and development of airborne direction finding methods (800-3000 Me) 

RP-298 

SC-97.06 

Research and development of airborne direction finding antennas (30-100 Me) 

RP-298b 



RP-404 



RP-444 

SC-98 

Special countermeasures services 


SC-98.01 

Construction of synthetic giant wurzburg 

RP-179 

SC-98.02 

Equivalent echoing areas of aircraft 

RP-269 

SC-98.03 

NDRC consultation on airborne RCM Installations 

RP-341 

SC-98.04 

NDRC consultation and advisor service on airborne RCM procurement 

RP-284 



RP-314 



RP-333 



R P-431 



RP-433 

SC-98.05 

Ferret antennas and tests 

RP-315 

SC-98.06 

RCM catalog and text 

RP-HAC 

SC-98.07 

Research and development of countermeasures vs. radio controlled missiles 

RP-361 



RP-362 



RP-382 



RP-383 



RP-384 



RP-388 



R P-389 

SC-98.08 

Magnetic countermeasures investigation 

RP-386 

SC-98.09 

Research of countermeasures against proximity fuses 

RP-117a, c, d 

SC-98.10 

RCM against radar blind bombing 

RP-474 

SC-98.98 

NDRC consultation and advisory service on procurement of ground-based RCM 

RP-314 


equipment 

RP-470 

SC-99 

RCM test equipment 


SC-99.01 

Test equipment for search receivers TS-47/APR 

RP-195 

SC-99.02 

Wavemeter for AN/APT- 1 and AN/APT-3 TS-99/AP 

RP-245 

SC-99.03 

Wavemeter for AN/APQ-2 TS-53/x'\P 

RP-290 

SC-99.04 

Spectrum analyzer TS-54/AP 

RP-175 

SC-99.05 

Pulse generator (RRL F-2200) 

RP-289 

SC-99.06 

Research and development of special test equipment required for airborne jam- 

RP-385 


ming systems (1000-3500 Me) 

RP-392 



RP-416 


510 


DIVISION 15 RESEARCH PROJECT NUMBERS AND ASSIGNMENTS 


Identification of Division 15 projects was accomplished by the assignment of an RP number to each project. The proj- 
ects were then assigned to a Division 15 Contractor or, in some cases, different phases of a given project was assigned 
to different contractors. 

The following list gives the RP number of each Division 15 project and the OEMsr number of the contract to which 
it was assigned. The contractor’s identity may be determined by cross-reference to Contract Numbers, pages 498-500. 


RP Number Subject Contract Number 


100a 

High-power ground jammer (Tuba) 

OEMsr-411 

100b 

Development of a prototype model of a 50 kw ground jammer 

OEMsr-411 

100c 

Tuba production model 

OEMsr-411 

103a 

Deception and confusion reflection (Chaff) 

OEMsr-411 

103b 

Window filler for mortar shells 

OEMsr-411 

106 

Homing on jammers (Fanny) 

OEMsr-411 

107 

Characteristics of cone antennas 

OEMsr-411 

107a 

Theory of impedance matching 

OEMsr-411 

107b 

Theoretical antenna studies 

OEMsr-41 1 

107c 

Waveguide components (3000-10,000 Me) 

OEMsr-411 

109 

Communication jamming effectiveness tests 

OEMsr-966 

109a 

Vulnerability of enemy communications receivers 

OEMsr-1024 

no 

Pulse repeater (moonshine) 

OEMsr-411 

112 

ABL-15 version of Boozer (AN/APR-3) 

OEMsr-411 

115 

Study of communication jamming (Jostle) 

OEMsr-966 

116 

High power tunable CW magnetrons 

OEMsr-931 

117 

Wide-band regenerative amplifier 

OEMsr-411 

117 

Proximity fuses from CM viewpoint 

OEMsr-411 

117a 

Proximity fuses countermeasures 

OEMsr-1305 

117b 

Airborne PF jammer 

OEMsr-1305 

117c 

Ground-based PF jammer 

OEMsr-1305 

117d 

Search receiver for proximity fuses 

OEMsr-1305 

122 

Listening through and jammer alignment systems 

OEMsr-993 

123 

Pulse communication jamming and anti-jamming studies 

OEMsr-895 

124 

Protected communication system 

OEMsr-937 

126 

Vulnerability of Loran to radio countermeasures 

OEMsr-411 

128 

Study of radar AJ circuits 

RL under 

NDRC Div.l4 

131 

AM vs. FM from AJ viewpoint 

OEMsr-895 

132 

Expendable communications jammer (Chick) 

OEMsr-940 

135 

Microwave search receiver (1000-3100 Me) (AN/APR-5) 

OEMsr-411 

135a 

X-band coaxial mixers for AN/ APR-5 receiver 

OEMsr-411 

136 

Pimpernel 

OEMsr-653, 867 


Pimpernel modification 

■ OEMsr-1045 

137 

Airborne antenna radiation patterns 

’ OEMsr-759 

138 

Design of specific antennas 

OEMsr-411 

139 

Autosearch receiver (90-1000 Me) (AN/APR-2) 

OEMsr-411 

140 

Blinker panoramic receiver 

OEMsr-867 

140 

Dustpan autosearch receiver 

OEMsr-411 

140 

Band-spread blinker 

OEMsr-1045 

141 

Tuning units for ARC-1, SCR-587, APR-1, APR-4 and SPR-1 

OEMsr-411 

144 

Unit construction receiver (AN/APR-1, -4, AN/SPR-1) 

OEMsr-411 

144a 

Modification of AN/APR-1 to increase output on pulsed signals 

OEMsr-411 

144b 

Conversion of AN/APR-1 i-f amplifier for spot jamming 

OEMsr-411 

145 

Superheterodyne wdth pre-selection 

OEMsr-411 

146 

R-C receiver 

OEMsr-411 

147 

Zero-Catcher I (RC-164B) 

OEMsr-411 

148 

Conversion of transmitters into jammers 

OEMsr-966 

149 

Wave propagation studies 

OEMsr-966 

150 

Barrage jammer (Jackal) (AN/ARQ-2) 

OEMsr-940 


Airborne barrage jamming system 

OEMsr-966 

151 

Research on barrage jammers (Pup) 

OEMsr-966 

152 

Study of spark jammer 

OEMsr-940 

153 

Conversion of WE ATR transmitter to jammer 

OEMsr-940 

154 

Dina for communication jamming 

OEMsr-940 


511 


RESEARCH PROJECTS {Continued) 


RP Number Subject 

Contract Number 

155 

Electro-mechanical FM jammer 

OEMsr-940 

156 

Electric pulse repeater Peter 

OEMsr-931 


Installation and operation of Peter 

OEMsr-1045 

157 

Investigation of persistent echoes from shells 

OEMsr-931 

158a 

Moderate power tunable CW magnetrons (Piccolo) 

X-band tunable CW magnetron (Type L-104) 

OEMsr-1019 

158b 

Moderate power tunable CW magnetron 

OEMsr-1357 

158c 

1-kw CW tunable magnetrons 

OEMsr-1430 

158d 

1-kw split anode magnetron 

OEMsr-1043 

158e 

1-kw CW tunable magnetrons 

OEMsr-1456 

158f 

1-kw CW tunable magnetrons (Piccolo) 

OEMsr-931 

159 

Jamming and anti-jamming of radio telegraphy 

OEMsr-936 

160 

Signal generator for 90-250 Me (AN/TPQ-T2) 

OEMsr-923 

161 

Carrier-less noise transmitter (Dina I) 

OEMsr-411 

162 

100-Mc transmitter 

OEMsr-411 

163 

Mandrel transmitter (AN/APT-3) 

OEMsr-411 


Modification of AN/APT-3 

OEMsr-1045 

164 

Rug transmitter (AN/APQ-2) 

OEMsr-411 

165 

Carpet I (AN/APT-2) 

OEMsr-411 


Carpet I modification 

OEMsr-1045 

165a 

Modification of AN/APT-2 (Carpet lA) 

OEMsr-41 1 

165b 

Film on Carpet spot jamming (AN/APT-2) 

OEMsr-411 

166 

Carpet III (AN/APQ-9) 

OEMsr-411 

166a 

Oscillator for converting APQ-1 to 145-350 Me 

OEMsr-411 

167 

Carpet Sweeper I (460-600 Me) (AN/APQ-1) 

OEMsr-411 


Carpet Sweeper I (460-600 Me) 

OEMsr-1045 

168 

VHF oscillators (L-3 Tube) 

OEMsr-411 

169 

Microwave jamming 

Microwave jamming transmitter 

OEMsr-411 

169a 

Oscillator research (1000-2000 Me) (AN/APQ-2 1) 

OEMsr-411 

169b 

S-Band tunable CW magnetron 

OEMsr-411 

169c 

R-F wattmeter for 1000-3000 Me range 

OEMsr-411 

170 

Zero Catcher homing device 

OEMsr-411 

171 

Susceptibility to jamming of the SCR-268 radar equipment 

OEMsr-411 

172 

Vulnerability of SCR-617/ASG 

OEMsr-411 

173 

Microwave oscillator (1000-3300 Me) 

OEMsr-411 

174 

Signal generator (1000-3000 Me) 

OEMsr-411 

175 

Spectrum analyzer (20-150 Me & 90-1000 Me) (TS-54/AP) 

OEMsr-411 

176 

Video spectrum analyzer 

OEMsr-411 

177 

Photography of cathode-ray tubes 

OEMsr-411 

178 

Power supplies (400-2600 cps) 

OEMsr-411 

179 

Synthetic giant Wurzburg 

OEMsr-411 

180 

Carpet practice jammer 

OEMsr-411 

181 

Theoretical study of noise 

OEMsr-411 

182 

Study of pulse jamming characteristics of pulses 

OEMsr-411 

183 

Crystal test equipment 

OEMsr-411 

184 

RF power measuring devices 

OEMsr-867 

185 

Wide range wavemeter (80-1000 Me) 

OEMsr-867 

186 

Basic study of jamming 

OEMsr-411 

187 

Wideband video transformers 

OEMsr-411 

187a 

Study of noise sources 

OEMsr-411 

187b 

Wideband transformers for noise 

OEMsr-411 

188 

Receiver for radar homing missile (Moth) (AN/APQ-14) 

OEMsr-411 

189 

Vulnerability of communication receivers 

OEMsr-1024 

190 

Monitoring of enemy signal (See Saw) 

OEMsr-966 

191 

Jamming signal generator (2400-3700 Me) 

OEMsr-411 

192 

Development of an externally modulated signal generator for range 20-40 Me 

OEMsr-1005 

193 

Search receiver for PF signals 

OEMsr-1045 

194 

Protected communication system 

OEMsr-937 

195 

Test oscillator for 40-500 Me (TS-47/APR & TS- 109/SPA) 

OEMsr-923 

196 

Electronic noise sources 

OEMsr-1060 


512 


RESEARCH PROJECTS {Continued) 


RP . 

Number Subject 

Contract Number 

197 

High-power communication jammer (Cigar) 

OEMsr-1107, 411, 1045 

198 

Expendable broadcast transmitter (Hen) 

OEMsr-895 

199 

Airborne communication jammer (Pad) (AN/ART-2) 

OEMsr-940 

200 

Power amplifiers for ARQ-10 (500 watts 1.3-45 Me) 

OEMsr-1275 

202 

Microwave autosearch receiver 

OEMsr-411 

203 

Wideband electronic FM 

OEMsr-411 

204 

Oscillator research in L-band 

OEMsr-411 

205 

GL 449 oscillator 

OEMsr-411 

207 

Jamming signal generator 

OEMsr-411 

208 

100/200 Me transmitter 

OEMsr-411 

209 

Homing receiver attachments (Tail) 

OEMsr-411 

210 

Pulse repeater (Stardust) 

OEMsr-411 

212 

Microwave tuning unit for APR-1, -4 

OEMsr-411 

213 

Study of propeller modulation 

OEMsr-411 

214 

Study of radar AJ circuits 

OEMsr-411 

214a 

Polarization cancellation system for AJ 

OEMsr-411 

215 

Super-regenerative receiver 

OEMsr-411 

217 

Study of frequency- modulated oscillators 

OEMsr-411 

218 

100-watt power amp. (85-150 Me) (AM-14/APT) 

Modification of AM-14/APT for LF 

OEMsr-411 

OEMsr-411 

221 

X-band field test jammer 

OEMsr-411 

222 

Vulnerability of SCR-521A/ASVC 

OEMsr-411 

223 

Vulnerability of ASB radar 

OEMsr-411 

224 

Vulnerability of FD radar 

OEMsr-411 

225 

Vulnerability of ASD-1 (AN/M^S-3) radar (AN/APS-1) 

OEMsr-411 

226 

Vulnerability of SCR-520 radar system 

OEMsr-411 

227 

AJ features of 7 unit printer 

OEMsr-895 

228 

AJ features of tape facsimile 

OEMsr-895 

229 

AJ possibilities of impulse and time code signalling systems 

OEMsr-895 

230 

Synchronous tracking (meandering) 

OEMsr-895 

231 

AJ features of status change device 

OEMsr-895 

232 

Double side-band Dina for jamming 

OEMsr-940 

233 

Audio noise sources (Gaston) 

OEMsr-966 

234 

Non-coherent pulses for jamming 

OEMsr-940 

235 

Jamming efficiency tests 

OEMsr-940 

237 

Expendable radar jammers 

OEMsr-411 

239 

Coaxial diode 

OEMsr-867 

240 

Multi-channel barrage jammer 

OEMsr-867 

241 

Signal generators 

OEMsr-867 

242 

Albatross I 

OEMsr-411 

243 

Constriction oscillator as noise source 

OEMsr-931 

244a 

Low-power tunable CW magnetrons (Flute) 

OEMsr-931 

244b 

X-band CW tunable magnetrons 

OEMsr-1043 

245 

Heterodyne frequency meter (55-250 Me) (TS-99/AP) 

OEMsr-411 

246 

Orange Squeezer 

OEMsr-411 

247 

Sealed-off resnatron 

OEMsr-1034 

248 

Microwave spark jammer 

OEMsr-411 

249 

Long distance sky wave jamming 

OEMsr-778, 966 

250 

Receiver for tuning Dina (Mate) (AN/ARQ-8) 

OEMsr-411 

251 

Miscellaneous microwave jamming devices 

OEMsr-411 

252 

Direction finding deception (Blanket) 

OEMsr-895 

253 

Infradyne tuning unit for SRC587/ARC-1 

OEMsr-411 

257 

Confusion reflectors (Rope) 

OEMsr-411 

258 

Corner reflectors (Angels) 

OEMsr-931 

258a 

Confusion reflectors (Angels) 

OEMsr-411 

258b 

Confusion reflectors (Kites) 

OEMsr-411 

259 

Communication antenna studies 

OEMsr-966 

260a 

Development of broadband antennas 

OEMsr-895 

260b 

Development of broadband, sleeve type, streamlined antennas 

OEMsr-895 

260c 

Broadband antennas for high-speed airplanes 

OEMsr-895 


513 


RESEARCH PROJECTS {Continued) 


RP Number Subject 

Contract Number 

260d 

Development of faired-in antennas 

OEMsr-895 


261 

Investigation of antenna reference material 

OEMsr-867 



Antenna system for Moth 

OEMsr-867 



Long-wire antennas 

OEMsr-867 



Wide-band low-frequency antennas 

OEMsr-867 



Pattern measurement of shipborne antennas 

OEMsr-867 


262 

Beaver 

OEMsr-411 


263 

Monitoring and tracking of CW signals 

OEMsr-895 


264 

Autosearch tuning unit (25-50 Me) 

OEMsr-867 



Modifications of communications autosearch receiver (Blinker) 

OEMsr-1045 


266 

931 Tube field test set 

OEMsr-411 


267 

Airborne suppressed-carrier noise jammer (25-104 Me) AN/ARQ-8 

OEMsr-411 


269 

Equivalent echoing areas of aircraft 

OEMsr-759 


270 

Crystal rectifier as peak voltmeters 

OEMsr-923 


271a 

Shipborne DF system heads 

OEMsr-411 


271b 

DF antenna for radar search 

OEMsr-411 


271c 

Directional antenna for radar search receiver 

OEMsr-411 


271d 

Microwave DF antenna (CFH-6613, AS-186/APA-17) 

OEMsr-411 


271e 

X-band antenna head for DBM DF system 

OEMsr-411 


271f 

Submarine DF for radar frequencies 

OEMsr-411 


271g 

Low-frequency DF antenna spinner for DBM 

OEMsr-411 


272a 

Power amplifier (500 watts, 14-60 Me) (AM-66/ARxr) 

OEMsr-940 


272b 

Field tests of AM-66/ARxr amplifier 

OEMsr-966 


273 

Consultant service (Navy) for APR-1, APR-2, APR-5 and APR-6 

OEMsr-411 


275 

Shipborne jamming transmitter using ZP-522 tubes (AN/SPT-6) • 

OEMsr-411 


276 

Recorder for AN/APR- 1, -4 & AN/SPR-1 receiver (AN/APA-23) 

OEMsr-411 


277 

Vulnerability of the SCR-717B radar 

OEMsr-411 


279 

Ground-based antenna for 90-210 Me 

OEMsr-411 


280 

Variable frequency microwave radar 

RL under 




NDRC Div. 

14 

281 

Consultant service to Radiation Laboratory on tunable microwave radar system 

OEMsr-411 


283 

Paint to absorb electromagnetic radiation 

RL under 




NDRC Div. 

14 

284 

Consultant service to the Army on the procurement of airborne RCM equipment 

OEMsr-411 


285 

L-band magnetron transmitter research 

OEMsr-411 


286 

Search receiver research 

OEMsr-411 


287 

Zero Catcher II 

OEMsr-411 


288 

Early warning receiver research 

OEMsr-411 


289 

Carpet Tester (TS-52/APQ-1) 

OEMsr-411 


290 

Carpet Checker (TS-53/AP) 

OEMsr-411 


291 

Microwave search receiver (3000-6000 Me) (APR-6) 

OEMsr-411 


292 

Test oscillator (2500-3500 Me) 

OEMsr-411 


293 

Alignment indicator for RF amplifier (TS-92/AP) 

Twin peaking alignment device 550 kc-10 Me 

OEMsr-411 


294 

Frequency standard and monitor for mandrel 

OEMsr-411 


295a 

S-band tunable magnetrons 

OEMsr-411 


295b 

Investigation of Sylvania SD-849 tube 

OEMsr-411 


295c 

Study of magnetrons 

OEMsr-411 


295d 

Investigations of low-power squirrel-cage S-band magnetrons 

OEMsr-411 


297 

Receiver (Lobster) for tail 

OEMsr-411 


298 

Development of DF methods 

OEMsr-411 


299a 

RCM wave propagation considerations 

OEMsr-411 


299b 

Propagation studies 

OEMsr-411 


299c 

Experimental determination of formation factor 

OEMsr-411 


301 

Simulated CM unit installation 

OEMsr-411 


302 

Albatross II 

OEMsr-411 


303 

Horizontal and circularly polarized RCM antennas 

OEMsr-411 


305 

Methods of modulating oscillators in L band 

OEMsr-411 


306 

Development of laboratory instruments 

OEMsr-411 


307 

Electronic tuning for panoramic reception 

OEMsr-1138 


308 

L-band ground jammer 

OEMsr-411 



514 


RESEARCH PROJECTS {Continued) 


RP Number Subject , Contract Number 


309 

Airborne suppressed carrier noise jammer (Dina II) (AN/APT-1) 

High frequency Dina, Dinamate transmitter j 

Antenna pattern measuring equipment 

OEMsr-411 

310 

OEMsr-867 

311 

Study of noise sources 

OEMsr-1176 

312 

Oscillator and modulator for Carpet IV 

OEMsr-867 

313 

Jamming simulator for Mark I radar trainer (TS-109SPA) 

OEMsr-411 

314 

Advisor service to the Army Signal Corps on RCM procurement 

OEMsr-411 

315 

Ferret installation studies 

OEMsr-411 

316 

Consultant service (GE) shipboard jamming transmitter 

OEMsr-411 

317a 

AJ training films 

OEMsr-411 

317b 

J and AJ photographs on Mark IV radar 

OEMsr-411 

318 

Integration methods for indicators 

OEMsr-411 

319 

Vacuum tube field pattern measurements 

OEMsr-867 

320 

Studies of gas discharge tubes 

OEMsr-867 

321 

High-power L-band transmitters 

OEMsr-411 

323 

Practice jammer for low-frequency Navy radar (AN/UPT-T4) 

OEMsr-411 

324 

Vulnerability of Navy airborne radar systems 

OEMsr-411 

325 

Search receivers and analyzers for pulse communications 

OEMsr-895 

326 

Communications jamming on maneuvers 

OEMsr-966 

327 

Jammer frequency setting 

OEMsr-411 

328 

Synthetic German AI transmitter 

OEMsr-411 

329 

Power amplifier (50 watts 140-210 Me) (AM-18/APT) 

OEMsr-411 

331 

Wide-band oscilloscope 

RF power meter and standing wave detector 

OEMsr-867 

332 

Oscillator tube research (X band) 

OEMsr-1222 

333 

Consultant service (Army SC) on production of Chaff 

OEMsr-411 

334 

Vulnerability of radio altimeters to jamming and development of AJ measures 

OEMsr-1305 

335 

Consultant service on shipboard transmitters 

OEMsr-411 

336 

Airborne barrage jammer (Carpet IV) (AN/APT-5) 

OEMsr-411, 867 

338 

Air Broadloom III (AN/APT-4) 

OEMsr-411 


Air Broadloom II (AN/APT-7) 

Development of AN/APT-8 transmitter 



L-band magnetron transmitter (Air Broadloom III) 

OEMsr-1045 

338a 

Investigation of bandwidth and relative jamming effectiveness of various transmitters 

OEMsr-411 

338b 

Study of transmitters for spot jamming 

OEMsr-411 

339 

Radar jamming system — Beaver III 

OEMsr-411 

340 

10-kw ground or ship magnetron transmitter 

OEMsr-411 

341 

Consultant service (ARL) on RCM aircraft installations 

OEMsr-411 

342 

High frequency Dinamate Receiver (Dinamate II) 

OEMsr-411 

343 

Installation of SCR-648 radar 

OEMsr-411 

344 

Power amplifier (100 watts, 35-100 Me) (AM-33/APT) 

OEMsr-411 

345 

Consultant service (SC) on RCM antennas 

OEMsr-895 

346 

100- watt jammer (90-400 Me) 

OEMsr-411 

347 

Spectrum analyzer (100-1400 Me) 

OEMsr-931 

348 

Training modulator for jamming transmitter (RF-9/UPT) 

OEMsr-411 

349 

Consultant service (AAF) on radar tow targets 

OEMsr-411 

350 

Fundamental studies of cavity oscillators 

OEMsr-411 

351 

10-kw magnetron tube development 

OEMsr-747 

352 

Antennas for horizontal polarization at UHF 

OEMsr-895 

353 

Resnatron development 

OEMsr-747 

354 

Consultant service to the Navy — re: broadband receiving antenna for submarine uses 

OEMsr-411 

355 

Vulnerability of RHB (Pelican) receiver 

OEMsr-411 

356a 

l5-kw communications jammer (38-52 Me) AN/MRT-1 (Cigar) 

OEMsr-1309, 1310 

356b 

Noise modulation for Cigar 

OEMsr-940 

356c 

Modification kits for Cigar (MX255/MRT-1) 

OEMsr-1310 

357 

Vulnerability of Mark 12 radar 

OEMsr-411 

358 

Airborne spot jammer system study 

OEMsr-966 

359 

Automatic search jammer (Broom) 

OEMsr-1305 

360 

Automatic-search jammer (Beagle) 

OEMsr-1305 

361 

Signal recording equipment (ARQ-12, SRQ-2) 

OEMsr-1305 

362 

Signal repeating jammer (Piano) 

OEMsr-1305 


515 


RESEARCH PROJECTS {Continued) 


RP Number Subject 

Contract Number 

363 

Panoramic receiver (Panther) 

OEMsr-1305 

364a 

Training jammer for Mark IV radar 

OEMsr-411 

364b 

Low-frequency jamming signal generator 

OEMsr-411 

367 

Vulnerability of the SCR-720 radar 

OEMsr-411 

368 

AJ study of AN/APG-1 radar system 

OEMsr-411 

378 

Investigation of 1-kw resnatron 

OEMsr-411 

379 

Consultant service (Navy) on procurement of DF equipment 

OEMsr-411 

380 

Automatic search and lock-on jamming system (Automat) (AN/APA-27) 

OEMsr-411 

381 

Modification of ARC-1 and SCR-587 receiver 

OEMsr-411 

382 

Studies of antennas and associated elements 

OEMsr-1305 

383 

Fundamental jamming and anti-jamming studies 

OEMsr-1305 

384 

Vulnerability of controlled devices 

OEMsr-1305 

385 

Jamming signal generator (2700-3300 Me) 

OEMsr-411 

386 

Magnetic countermeasures investigation 

OEMsr-1305 

387 

Navy AJ instructor training course 

OEMsr-411 

387a 

AN /APA-48 training program 

OEMsr-411 

388 

1-kw amplifier 

OEMsr-1305 

389 

Multiple-channel exciter system for GM CM (AN/SRQ-1) 

OEMsr-1305 

391 

Consultant service (Navy) on the development of a high-powered shipborne trans- 



mitter 

OEMsr-411 

392 

Spectrum analyzer (10-3500 Me) 

OEMsr-931 

394 

5-kw plane Parallel tetrode (L-201) 

OEMsr-931 

395 

Medium power GM jammer (MAS) 

OEMsr-1305 

397 

Evaluation of communication transmitter performance 

OEMsr-1024 

398 

Research on 1-kw transmitter 

OEMsr-411 

399 

Antenna impedance measurements 

NDrc-100 

402a 

RF switches (CLU-24314) 

OEMsr-1305 

402b 

4-way coaxial switches 

OEMsr-1305 

403 

X-band transmitter research 

OEMsr-411 

404 

Model study of airborne direction finders 

NDCrc-100 

405a 

1-kw ground jammer 

OEMsr-411 

405b 

Wide band coaxial line 

OEMsr-411 

406 

AJ methods for Window 

OEMsr-411 

406a 

Study of radar AJ circuits 

OEMsr-411 

406b, f 

Window dispensing devices 

OEMsr-411 

406c 

Window pilot factory 

OEMsr-411 

406d 

Confusion reflectors (basic research) 

OEMsr-411 

406e 

Theory of reflectors 

OEMsr-411 

406g 

Radiation measurements of Window 

OEMsr-867 

406j 

Detection of radar decoy reflectors 

OEMsr-411 

407 

Investigation of negative-grid high-frequency tubes 

OEMsr-411 

408a 

Wide range, tunable direct detection receiver (Spud I) (AN/APR-7A) 

OEMsr-411 

408b 

Wide range, tunable direct detection receiver (Spud II) (AN/APR-8) 

OEMsr-411 

408c 

Wide range, tunable direct detection receiver (Spud III) 

OEMsr-411 

409 

RF power indicator 

OEMsr-411 

410 

Trailing coaxial dipole antenna (Stingeree) 

OEMsr-966 

411 

AJ investigation of AN/APS-4 

OEMsr-411 

414 

Airborne S-band jammer 

OEMsr-411 

415 

Shipborne S-band klystron jammer 

OEMsr-411 

416a 

Microwave test oscillator 

OEMsr-411 

417a 

Investigation of L-band Piccolo-series magnetron 

OEMsr-411 

417b 

Investigation of S-band magnetron 

OEMsr-411 

418 

Low-power S-band CW tunable magnetron 

RL under 

NDRC Div. 14 

419a, b 

L5-kw airborne GM jammer (AN/ARQ-11, SRQ-11) 

OEMsr-1305 

420a 

Modification of FM transmitter (AN/GRQ-1) 

OEMsr-1305 

420b 

Antenna system for GRQ-1 

OEMsr-1305 

421 

Development of MAS type receiver (AN/ARQ-11) 

OEMsr-1305 

422 

Radio navigational aids — CM Study 

OEMsr-966 

424 

Airborne S-band magnetron transmitter (AN/APQ-20) 

OEMsr-411 

425a 

Panoramic unit (Panda) (AN/APA-41) 

OEMsr-411 


516 


RESEARCH PROJECTS (Continued) 


RP Number Subject ^ 

Contract Number 

425b 

Panoramic unit (Panda) 

OEMsr-1305 

426 

Consultant service (Navy) on the Elephant jamming system 

OEMsr-411 

427 

Ground planes for antenna model measurements 

OEMsr-759 

428 

Airborne jammer for S band (1000-2500 Me) 

OEMsr-411 

429 

Army RCM training courses 

OEMsr-411 

430a 

S-band amplifier tubes 

25-watt CW tunable magnetrons 

OEMsr-931 

430b 

Low-power CW tunable magnetrons 

OEMsr-1456 

431 

Consultant service (Army) on RCM procurement 

OEMsr-1305 

432 

Meteorological observations for propagation studies 

OEMsr-1305 

433 

Consultant service (Army) on tube procurement 

OEMsr-931 

434 

Consultant service (Navy) on tube procurement 

OEMsr-1019 

435a 

Single signal receivers 

OEMsr-411 

435b 

Tuning unit for single signal receivers 

OEMsr-411 

435c 

X-band tuning unit for single signal receivers 

OEMsr-411 

436 

Vulnerability of control equipment Mark II (Bat) 

OEMsr-411 

437 

Airborne direction finder flight testing 

OEMsr-936 

438 

Spec, broadband signal repeating system 

OEMsr-411 

439 

Consultant service on vacuum tubes 2K48 (1429CT-8) and 2K49 (1429CT-9) 

OEMsr-1222 

440a 

Communications Ferret systems study 

OEMsr-966 

440b 

Ferret systems design 

OEMsr-966 

441 

Communication countermeasures studies 

OEMsr-966 

442 

Assistance to Radiation Laboratory on AEW project 

OEMsr-411 

442a 

Intercept receiver filters 

OEMsr-411 

442b 

Microwave filter development 

OEMsr-411 

443 

General improvements for existing search receivers 

OEMsr-411 

444 

Airborne direction finding system (1.5-100 Me) 

OEMsr-1458 

445 

Instrumental susceptibility to countermeasures of navigation direction finders 

OEMsr-1458 

446 

Study of test equipment 

OEMsr-411 

447 

AJ applications to receivers 

OEMsr-411 

448 

Blanking circuit for search receivers (Silent Knight) 

OEMsr-411 

449 

AJ investigation of the AN/APA-16 as used with APS-4 

OEMsr-411 

450 

Consultant service to Psycho-Acoustical Laboratory 

OEMsr-1024 

451 

Effect of receiver circuits on susceptibility to jamming 

OEMsr-1024 

452 

AJ investigation of APQ-5B 

OEMsr-411 

453 

Evaluation tests on TPL-1 

OEMsr-411 

454 

S-band spot jamming system (AN/APQ-20, -27) 

OEMsr-411 

455 

300 to 2500 Me spot jamming system 

OEMsr-411 

457 

Elephant system, design, and assembly 

OEMsr-411 

458 

200 Me GL airborne jamming system 

OEMsr-411 

459 

1100 Me A1 jamming system 

OEMsr-411 

460 

Vulnerability to jamming of pulse communication system 

OEMsr-895 

461a 

1-kw shipborne transmitter for Elephant jamming system 

OEMsr-411 

461b 

Study of operating characteristics of the 6J21 (612) tube for use in the Elephant 
jamming system 

OEMsr-411 

461c 

Low-frequency oscillator for Elephant jamming system 

OEMsr-411 

462a 

Receiver for Elephant jamming system 

OEMsr-411 

462b 

P.R.F. and pulse width indicator 

OEMsr-411 

462c 

Unit shipborne receiver 

OEMsr-411 

462d 

X-band head for Elephant receiver 

OEMsr-411 

463 

Development of a frequency modulator for the 605B standard signal generator 

OEMsr-1005 

464 

P-551 amplifier 

OEMsr-1005 

465 

Signal generator for 20-156 Me 

OEMsr-1005 

466 

P-553 signal generator 

OEMsr-1005 

467 

Frequency multiplier for P-519 signal generator 

OEMsr-1005 

468 

Microwave signal generator 

OEMsr-411 

469 

Microwave standard signal generator 

OEMsr-411 

470 

Consultant service (Army) on the procurement of ground-based RCM equipment 

OEMsr-411 

471 

Ferret DF antenna trainer 

OEMsr-411 

472 

RF connectors 

OEMsr-411 

473 

Audio-frequency amplifier 

OEMsr-411 


517 


RESEARCH PROJECTS {Continued) 


RP Number Subject 

Contract Number 

474 

RCM for radar blind bombing 

OEMsr-411 

475 

AJ study of SCR-545 

OEMsr-411 

476 

Spark excited signal generators 

OEMsr-411 

477 

Airborne RCM operator’s manual 

OEMsr-411 

478 

Assistance to the operations research group 

OEMsr-411 

479 

Microwave wattmeter 

OEMsr-411 

480 

Rad Seven — radar countermeasures manual 

OEMsr-411 

481 

Miscellaneous interim antennas 

OEMsr-411 

483 

Model antenna pattern measurements 

OEMsr-1305 

484 

Development of faired-in antennas for high-speed aircraft 

OEMsr-1305 

974 

Advanced service base 

OEMsr-1045 

975 

Communications deception device 

OEMsr-1045 

976 

Emergency aid to 9th AAF on high-frequency communications 

OEMsr-1045 

977 

Investigation of enemy jamming 

OEMsr-1045 

979 

Guided missile investigation 

OEMsr-1045 

980 

Receivers for spot jamming 

OEMsr-1045 

981 

Window activities in ETO 

OEMsr-1045 

982 

Ground search band 

OEMsr-1045 

983 

Reduction of interference from CSFR-TDY transmitter 

OEMsr-1045 

984 

Study of airborne antennas 

OEMsr-1045 

985 

Naval investigational program 

OEMsr-1045 

986 

Installation of Jackal (ART-3) 

OEMsr-1045 

987 

Barrage jamming installations 

OEMsr-1045 

988 

Ground-based antenna for communications AJ (3-6 Me & 20-28 Me) 

OEMsr-1045 

989 

Study of ?AN/APT-4 transmitter 

OEMsr-1045 

990 

Searchlight receiver 

OEMsr-1045 

991 

Modification of receiver to eliminate pulse interference 

OEMsr-1045 

992 

Antenna for Pimpernel 

OEMsr-1045 

993 

Screening of aircraft 

OEMsr-1045 

994 

Investigation aircraft 

OEMsr-1045 

995 

Modification of British ground Cigar for spot jamming 

OEMsr-1045 

996 

Tests of British Carpet II 

OEMsr-1045 

997a 

Carpet spot jamming 

OEMsr-1045 

997b 

Modification of AN/APT-2 

OEMsr-1045 

998a 

Enemy radar frequency and characteristics 

OEMsr-1045 

998b 

Operational testing of APR-2 

OEMsr-1045 

998c 

Enemy utilization of radar 

OEMsr-1045 

998d 

Location of enemy radar sites 

OEMsr-1045 

998e 

Efficacy of RCM equipment 

OEMsr-1045 

998f 

Investigation of enemy communications 

OEMsr-1045 

999a 

Recording for airborne VHF interception work 

OEMsr-1045 


518 


PROJECTS ASSIGNED TO DIVISION 15 CONTRACTORS 


The projects assigned by Division 15 to each of its contractors are given in the following list by RP numbers. The title 
of each RP number may be found in the pages immediately preceding. 


NDCrs-lOO 

OEMsr-411 {Contd.) 

OEMsr-411 {Contd.) 

OEMsr-411 {Contd.) 

RP-399 

RP-206 

RP-302 

RP-398 

R P-404 

RP-207 

RP-303 

RP-400 

OEMsr-63 

RP-381 

RP-208 

RP-209 

RP-304 

RP-305 

RP-401 

RP-403 

RP-210 

RP-306 

RP-405 

OEMsr-411 

RP-212 

RP-309 

RP-406 

RP-lOO 

RP-213 

RP-313 

RP-407 

RP-103 

RP-214 

RP-314 

RP-408 

RP-106 

RP-215 

RP-315 

RP-409 

RP-107 

RP-216 

RP-316 

RP-411 

RP-110 

RP-217 

RP-317 

RP-412 

RP-112 

RP-218 

RP-318 

RP-413 

RP-126 

RP-221 

RP-321 

RP-414 

RP-135 

RP-222 

RP-323 

RP-415 

RP-138 

RP-223 

RP-324 

RP-416 

RP-139 

RP-224 

RP-327 

RP-417 

RP-141 

RP-225 

RP-328 

RP-424 

RP-144 

RP-226 

RP-329 

RP-425a 

RP-145 

RP-237 

RP-333 

RP-426 

RP-146 

RP-242 

RP-335 

RP-428 

RP-147 

RP-245 

RP-336 

RP-429 

RP-161 

RP-246 

RP-338 

RP-435 

RP-162 

RP-250 

RP-339 

RP-436 

RP-163 

RP-251 

RP-340 

RP-438 

RP-164 

RP-253 

RP-341 

RP-442 

RP-165 

RP-257 

RP-342 

RP-443 

RP-166 

RP-258b 

RP-343 

RP-446 

RP-167 

RP-262 

RP-344 

RP-447 

RP-168 

RP-266 

RP-346 

RP-448 

RP-169 

RP-267 

RP-348 

RP-449 

RP-170 

RP-271 

RP-349 

RP-452 

RP-171 

RP-273 

RP-350 

RP-453 

RP-172 

RP-275 

RP-354 

RP-454 

RP-173 

RP-276 

RP-355 

RP-455 

RP-174 

RP-277 

RP-357 

RP-456 

RP-175 

RP-279 

RP-364 

RP-457 

RP-176 

RP-281 

RP-366 

RP-458 

RP-177 

RP-284 

RP-367 

RP-459 

RP-178 

RP-285 

RP-368 

RP-461 

RP-179 

RP-286 

RP-369 

RP-462 

RP-180 

RP-287 

RP-370 

RP-468 

RP-181 

RP-288 

RP-371 

RP-469 

RP-182 

RP-289 

RP-372 

RP-470 

RP-183 

RP-290 

RP-373 

RP-471 

RP-186 

RP-291 

RP-374 

RP-472 

RP-187 

RP-292 

RP-375 

RP-474 

RP-188 

RP-293 

RP-376 

RP-475 

RP-191 

RP-294 

RP-377 

RP-476 

RP-193 

RP-295 

RP-378 

RP-477 

RP-202 

RP-297 

RP-379 

RP-478 

RP-203 

RP-298 

RP-380 

RP-479 

RP-204 

RP-299 

RP-385 

RP-480 

RP-205 

RP-301 

RP-391 

RP-481 


519 


OEMsr-653 

RP-136 

OEMsr-747 

RP-351 

RP-353 

OEMsr-759 

RP-137 

RP-269 

RP-427 

OEMsr-867 

RP-136 

RP-140 

RP-184 

RP-185 

RP-239 

RP-240 

RP-241 

RP-261 

RP-264 

RP-310 

RP-312 

RP-319 

RP-320 

RP-336 

RP-331 

RP-406g 

OEMsr-895 

RP-123 

RP-131 

RP-198 

RP-227 

RP-228 

RP-229 

RP-230 

RP-231 

RP-252 

RP-260 

RP-263 

RP-268 

RP-325 

RP-345 

RP-352 

RP-420b 

RP-460 

OEMsr-923 

RP-160 

RP-195 

RP-245 

RP-270 

OEMsr-931 

RP-116 

RP-156 


PROJECTS ASSIGNED TO DIVISION 15 CONTRACTORS {Continued) 


OEMsr-931 (Contd.) 

OEMsr-1005 

RP-157 

RP-192 

RP-158f 

RP-463 

RP-243 

RP-464 

RP-244a 

RP-465 

RP-258a 

RP-466 

RP-347 

RP-467 

RP-392 

RP-394 

OEMsr-1019 

RP-430a 

RP-158a 

RP-433 

RP-434 

RP-434 

OEMsr-936 

OEMsr-1024 

RP-109a 

RP-159 

RP-189 

RP-437 

RP-397 

OEMsr-937 

RP-450 

RP-451 

RP-124 

RP-194 

OEMsr-1034 

OEMsr-940 

RP-247 

RP-132 

OEMsr-1043 

RP-150 

RP-152 

RP-158d 

RP-153 

RP-244b 

RP-154 

OEMsr-1045 

RP-155 

RP-999 

RP-199 

RP-998 

RP-232 

RP-997 

RP-234 

RP-996 

RP-235 

RP-995 

RP-272a 

RP-994 

RP-326 

RP-993 

RP-356b 

RP-992 

OEMsr-966 

RP-991 

RP-109 

RP-990 

RP-115 

RP-989 

RP-132 

RP-988 

RP-148 

RP-987 

RP-149 

RP-986 

RP-150 

RP-985 

RP-151 

RP-984 

RP-233 

RP-983 

RP-249 

RP-982 

RP-259 

RP-981 

RP-268 

RP-980 

RP-272b 

RP-979 

RP-326 

RP-977 

RP-358 

RP-976 

RP-422 

RP-975 

R P-440 

RP-974 

R P-441 

OEMsr-993 

OEMsr-1060 

RP-196 

RP-122 

RP-150 

OEMsr-1107 

RP-358 

RP-197 


OEMsr-1138 

RP-307 

OEMsr-1176 

RP-311 

OEMsr-1222 

RP-332 

RP-439 

OEMsr-1275 

RP-200 

OEMsr-1305 

RP-117a 

RP-117b 

RP-117C 

RP-117d 

RP-334 

RP-359 

RP-360 

RP-361 

RP-362 

RP-363 

RP-382 

RP-383 

RP-384 

RP-386 

RP-388 

RP-389 

RP-395 

RP-402 

RP-419 

RP-420a 

RP-421 

RP-425b 

RP-431 

RP-432 

RP-473 

OEMsr-1309, OEMsr-1310 
RP-356 
RP-356a 
RP-356C 

OEMsr-1357 

RP-1586 


OEMsr-1430 

RP-158C 


OEMsr-1456 

RP-158e 

RP-430b 


OEMsr-1458 

RP-444 

RP-445 


520 


INDEX 


The subject indexes of all STR volumes are combined in a master index printed in a separate volume. 

For access to the index volume consult the Army or Navy Agency listed in the reverse of the half-title page. 


A-131 tunable magnetron, 40, 43, 425 

A-132 multianode magnetron, 44-45 

A-133 multianode magnetron, 44-45 

ABL (American British Laboratory), 
radio countermeasures, 287-299, 
457 

A-f (audio frequency) noise generators, 
451-452 

Gaston, 22, 175 
magnetic, 22 

AI radar (aircraft interception), count- 
ermeasures to, 11-12, 140, 461 

AIL 

see Airborne Instruments Labora- 
tory 

Air Broadloom (jammer for radar), 386 

Air Cigar (British jamming system), 
299-300 

Air Mark VI (Japanese) radar, 334- 
335 

Airborne antennas, 60-65 
broad-band system, 442 
directivity patterns, 55, 433, 441 
directly-fed wing antennas, 65 
faired-in antennas, 65 
formula for power limit, 443 
frequency range, 55 
lobe-switching antenna, 439-440 
mounting, 57 

sleeve-type, 65, 435-436, 443, 445 
studies on models, 141-143 
summary of types, 60-63 
trailing-wire antennas, 64-65, 443 
V-antennas, 64 

Airborne Instruments Laboratory 
antennas and power transmission for 
nonradar countermeasures, 54- 
65 

jamming and antijamming tech- 
niques, 188-200 

jamming transmitters, 160-187 
magnetic tape recorders, 159 
radio countermeasures, test methods 
and equipment, 66-75 
receiving and direction-finding tech- 
niques, 149-159 

theoretical studies of jamming, 80- 
146 

Airborne jammers, 222-225 
advantages, 128, 215 
AN/APQ-20 (XA-2), 228 
AN/ARQ-8; 174, 183, 222-225 
AN/ARQ-11; 183-184 
Carpet, 275-282, 289-292, 361-363, 
385-387 

communication ferret C-1; 150-151, 
456 

CXCE, 384 
Dina, 384 


disadvantages, 11 
effectiveness against radar, 222 
Jostle IV, 456 
Mandrel, 267, 383-384 
1.5-kw, 392 
Pimpernel, 389 
preset frequency, 169 
Rug, 384-385, 457 

Aircraft-interception radar, counter- 
measures to, 11-12, 140, 461 
AJ techniques 

see Antijamming techniques 
Alignment systems for jammers, 397 
double-peaking amplifier-alignment 
unit, 76 

quado, 178-179, 394 
recommendations for future research, 
179 

Stopwatch, 179, 394 
Altimeters, radio 
AN/ARN-1; 196-197 
f-m, 413 

German, 140, 196-197, 454-455 
vulnerability to jamming, 140, 196- 
197, 413 

Aluminum foil, use in Chaff, 231, 235, 
409 

AM-33 amplifier, jamming effective- 
ness, 383 

AM-66/AR-XR power amplifier, use 
for jamming, 176, 382-383 
AM-80/ARA-13 airborne amplifier, 177 
AM-96/ARA-13 airborne amplifier, 177 
A-m communication, vulnerability to 
jamming, 193, 395, 397 
A-m jamming 

see Amplitude-modulated jamming 
A-m receivers, high-frequency, 193 
American British Laboratory, radio 
countermeasures, 287-299, 457 
Amplifier back-biasing circuit for anti- 
jamming, 252 

Amplifier-alignment unit, double-peak- 
ing, 76 

Amplifiers for jamming systems 
AM-33; 383 

AM-66/AR-XR, 176, 382-383 
AM-80/ARA-13; 177 
AM-96/ARA-13; 177 
AN/ARA-13; 177 
double-peaking alignment unit, 76 
Amplitude-modulated communication, 
vulnerability to jamming, 193, 
395, 397 

Amplitude-modulated jamming 
by noise, 81-84 
Dina, 162, 170 
effectiveness, 429-432 
noncoherent pulses, 171 


simultaneous f-m and a-m, 81-84, 
109 

spark sets, 171-172 
transmitter design, 170-172 
vulnerability of communications re- 
ceivers, 193 

AN-148A antenna, 440 
AN/APA-11 pulse analyzer, 417 
AN/APA-17 direction finder, 288, 457 
AN/APA-27 automatic jammer, 226- 
228, 388-389 

AN/APA-42T1 DF antenna trainer, 
422 

AN/APG-1 gun-laying radar, antijam- 
ming characteristics, 404 
AN/APG-1 gun-laying radar, suscepti- 
bility to jamming, 257, 404 
AN/APG-4 bombsight, vulnerability to 
jamming, 197 

AN/APN-1 altimeter, vulnerability to 
jamming, 196-197 

AN/APQ-5B blind bombing attach- 
ment, jamming susceptibility, 
404 

AN/APQ-9 

see Carpet (jamming transmitter) 
AN/APQ-20 airborne jammer for radar, 
228 

AN/ APR-5 radar search receiver, 373 
AN/APS-4 radar, jamming suscepti- 
bility, 257, 404, 461 
AN/APS-19 radar, antijamming modi- 
fications, 251 
AN/APT-1 jammer, 384 

design considerations, 170, 218 
jamming effectiveness, 167, 430 
noise clipping, 85, 88 
AN/APT-2 

see Carpet (jamming transmitter) 
AN/APT-4 jammer for radar, 386 
AN/APT-5 

see Carpet (jamming transmitter) 
AN/APT- 10 magnetron transmitter, 
387-388 

AN/ARA-13 airborne amplifier, 177 
AN/ARC-4 receiver, vulnerability to 
jamming, 193 

AN/ARN-1 altimeter, vulnerability to 
jamming, 196-197 
AN/ARQ-2 Jackal jammer, 395 
AN/ARQ-8 airborne jamming system, 
222-225 

applications, 183 
Dina transmitter, 174 
AN/ARQ-10 spot jammer, 176-177 
AN/ARQ-1 1 airborne jamming system, 
183-184 

AN/ARQ-1 2 airborne magnetic tape 
recorder, 156-158, 380 


521 


522 


INDEX 


AN/ART-2 pulse jammer, 381-382 
modulation, 174 
requirements, 174 
use against walkie-talkies, 382 
AN /ART-3 high-power Jackal jammer, 
383, 456 

Angels (corner reflector), 241-243 
construction, 230-231, 242-243, 412 
echoes from, 411 
effects of diffraction, 116-117 
folding reflector, 412 
reflection patterns, 411 
required characteristics, 241 
AN/GRQ-1 ground-based jammer 
antenna system, 64 
installation, 180-181 
modifications to commercial equip- 
ment, 180 

use against guided missiles, 393 
AN/SRQ-1 ship-borne jammer, 186- 
187, 392 

AN /SRQ-2 magnetic tape recorder, 
156-158, 381 

AN/SRQ-1 1 ship-borne jamming sys- 
tem, 183, 185 

AN/SRW-2 receiver, jamming vulner- 
ability, 195, 402-403 
Antenna selection switch, 435, 445 
Antenna trainer, direction-finding, 422 
Antennas, 54-65, 433-445 
broad-band, 442 
coaxial dipole, 445 
cone, 434, 439 
continuously-rotating, 440 
cylindrical, 439, 445 
end-fed balanced, 437-438 
fan dipoles, 445 
fishhook, 296-297, 436 
horn-type, 436 
lobe-switching, 439-440 
long-wire, 443 
loop antennas, 440 
S-band, 441 

sleeve, 65, 436, 443, 445 
slot, 436-437, 444 
spinners, 377-378 
split can, 436, 439 
stingaree, 445 
stub, 433, 435, 443 
TDY, 342 

trailing-wire, 64-65, 443 
u-h-f, 444 
V-antenna, 64 
wave, 64, 443-444 
waveguide, 434 
whip, 440-441 
wing, 65 

Antennas, design, 54-58 
antenna array, 55-56 
bandwidth, 54-55 


effect of diameter, 55 
effect of mounting at an angle, 57 
for direction finders, 455-456 
installation, 57 

optimum height of jamming antenna, 
440 

polarization, 56 

transmission lines and accessories, 58, 
63 

use of reflectors and wave guides, 55- 
56 

Antennas, radiation patterns, 440- 
444 

cone antennas, 441 
continuous antenna patterns, 441 
dipole on AT- 11 aircraft, 441 
effects of antenna coupling, 443-444 
loop antennas, 443-444 
measurement, 141, 433, 439 
search antennas, 438, 440 
ship-borne, 55-56, 443 
sleeve antennas, 443 
slot antennas, 442 
steel antenna, 443 
stingaree antenna, 445 
stub antennas, 441 
tank antennas, 433 
whip antennas, 441 
Antennas, scaled models 
airborne antennas, 141-143 
ground-based antennas, 143 
loop antennas, 375 
measurement of radiation patterns, 
141 

methods for measuring antenna im- 
pedances, 143 
shipboard antennas, 143 
Antennas, theoretical studies, 123-127 
cylindrical antennas, 123-124 
equivalent point antenna, 124-125 
general problems, 123-125 
loop antennas, 125-126 
search antennas, 126-127 
Antijamming techniques, 188-190, 250- 
254, 259-263, 405-406 
alternate operating frequencies, 14 
anti-window devices, 253-254 
back-biased i-f amplifier, 252 
basic principles, 188-189 
clipper stages in pulse f-m systems, 
191 

committee on antijamming, 250-251 
filters, 252, 259-260, 405 
f-m adapter for radio receivers, 190, 
398 

frequency coverage, 189 
gain control, 252 

jamming cancellation systems, 253- 
254 

L-901 video unit, 259 


listening-through systems, 173, 177- 
178 

lobe-switched radar, 253 
oscillator detuning attachment, 253, 
259 

pass circuit in pulse receivers, 191, 398 
peak clipping of audio voltages, 401 
personnel training, 14, 189, 261-262, 
421-422 

radio-printing attachment, 198-200 
recommendations, 262-263 
remote-tuning transmitter attach- 
ment, 260 

test equipment for jamming vulner- 
ability, 66-68 
use of audio limiter, 190 
use of high directivity, 14 
video amplifiers, 406 
Anti-window device, 117-122, 253-254 
effectiveness, 118-121 
reduction in pulse length, 117-118 
requirements, 121-122 
AN/TPL-1 searchlight-pointing radar, 
jamming susceptibility, 257, 404 
AN/TRC-1 field teletype equipment, 
jamming vulnerability, 194, 401 
AN/TRC-5 pulse communication sys- 
tem, jamming vulnerability, 194- 
195, 399 

AN/TRC-8 transmitter-receiver, elec- 
trical characteristics, 402 
AN/TRR-2 mine detonator, jamming 
vulnerability, 195, 402 
AN/UPT-1 practice jamming set, 261- 
262 

AN/UPT-T4 practice jamming set, 
261-262, 420 

Aperiodic meter, detection of radar 
signals, 95 

APQ-2 jammer for radar, 384-385 
advantages, 384 

modifications for spot jamming, 457 
APT-1 transmitter 

see Dina jammer (direct-noise ampli- 
fication) 

APT-3 transmitter, 267, 383 
ARB aircraft receiver, jamming vulner- 
ability, 402 

ARC-1 receiver, performance character- 
istics, 398 
ARQ-8 transmitter 

see Dina jammer (direct-noise ampli- 
fication) 

AS-44/APR-5 cone antenna, 434 
AS-69 fishhook antenna, 296-297 
AS-97/ART whip antenna, 440 
AS-161/ART whip antenna, 440 
AS-181/APT sleeve antenna, 435-436 
AS-222/APA-17 antenna spinner sys- 
tem, 377-378 


INDEX 


523 


ASB radar, antijamming modifications, 
260, 405-407 

ASG radar, antijamming character- 
istics, 403 

ASV radar, susceptibility to jamming, 
257 

ATR transmitter, conversion to bar- 
rage jammer, 382 
Audio detection of radar signals 
advantages, 431-432 
pulse length, 95 
sensitivity, 95 

signal-to-noise ratio perceived in ear- 
phone, 94 

Audio limiter for communications anti- 
jamming, 190 
Audio noise generators 
Gaston, 22, 175 
magnetic, 22 
Tungar bulbs, 452 

Audio oscillator, use with pulse ana- 
lyzer, 414 

Audio spectrum analyzers, 30-31 
Audio waveform for communications 
jamming modulation, 162 
Autodyne receivers for spot jamming, 
288 

Automatic jammers, 220-221 
Automat, 226-228, 388-389 
Beagle, 182 
Broom, 181-182, 393 
Carpet II, 290, 300, 387 
Pimpernel, 226, 389 
summary of types, 224-225 
theory of automatic tuning, 397 
Automatic search receivers, 205, 374 

BA-348-R receiver, vulnerability to 
jamming, 193 

Bagful (recording receiver), 278-279, 
287, 299 

Bagpipes (communication jamming 
modulation), 165 

Balancing transformer, wide-band, 134 
Ballantine Laboratories 
Gaston noise generator, 22, 175 
noise jamming sources, 19-38 
Bandwidth adjustment indicator, 417 
Barrage jammers, 168-169, 174-176, 
216-217, 381-383 
Carpet, 275, 345-346 
comparison with spot jammers, 168, 
216 

converted communications transmit- 
ters, 172, 175, 382 
definition of barrage jamming, 216 
disadvantages, 345-346 
effectiveness for 27-42 me communi- 
cations, 383 
evaluation, 168, 276 
expendable jammer (Chick), 174-175 


15-kw ground jammer (Cigar), 140, 
175-176, 389, 400 
f-m jammers, 382, 396 
frequency setting, 76, 168, 219-220 
Jackal, 383, 395, 456, 458 
Jostle IV, 456 
Mandrel, 267, 384 

noncoherent pulse jammer (Pad), 
174, 381-382 
operation, 168 
requirements, 107-108 
tests with r-f noise, 394 
transmitter design, 216 
type of modulation, 168, 216 
spark sets, 171-172, 382 
Bazooka transformer, frequency char- 
acteristics, 433 

BC-312-N receiver, jamming vulner- 
ability, 193, 401-402 
BC-342-N receiver, jamming vulner- 
ability, 193, 401 

BC-348-R receiver, jamming vulner- 
ability, 401-402 
BC-603-D receiver 
f-m adapter, 398 

jamming vulnerability, 193-194, 400 
BC-624-A receiver, jamming vulner- 
ability, 400-401 

BC-624-AM receiver, jamming vulner- 
ability, 193 

BC-625-A receiver, jamming vulner- 
ability, 401 

BC-639-A search receiver 
jamming vulnerability, 193, 401 
modifications to reduce pulse inter- 
ference, 371 

BC-652-A receiver, jamming vulner- 
ability, 193, 401-402 
BC-654-A receiver, jamming vulner- 
ability, 193, 401 

BC-659-A receiver, jamming vulner- 
ability, 400-402 

BC-669-C receiver, jamming vulner- 
ability, 193, 401-402 
BC-699-C receiver, jamming vulner- 
ability, 401 

BC-IOOO-A receiver, jamming vulner- 
ability, 401 

BC-1255A frequency meter, 417 
BC-1375 antijamming video filter, 259, 
405 

Beagle (automatic search jammer), 
182 

Beaver III (ground-based radar jam- 
mer), 284 

Beechnut (ideograph transmission sys- 
tem), 198, 399 
Bell Telephone Laboratories 
communications ferret, 150-151 
Gaston noise generator, 22, 175 
jamming modulations, 81 


jamming transmitters, 160-187 
local oscillator tubes, 40-41 
noise jamming sources, 19-38 
nonradar receiving and direction-find- 
ing techniques, 149-159 
photomultiplier tube, 19-20 
“propagation curves,” 127 
theoretical studies of jamming, 80- 
146 

vacuum tube development, 39-53 
Beverage wave antenna, 64 
Big Ben (German V-2 rocket), 300 
Birdnesting (phenomenon of dipoles), 
231 

Blanket (direction-finding deception), 
152-153, 412 
antenna, 153 

crystal-controlled oscillators, 153 
Blind bombing, jamming susceptibility, 
404 

Blinker (search receiver), 287-288 
Bomber navigational aids 
countermeasures to, 151, 413 
types, 264 

Bombsights, vulnerability to jamming, 
197 

Boozer (radar warning receiver), 206, 
287, 299 
British research 
Air Cigar, 299-300 
American British Laboratory, 287- 
299, 457 

Bagful (recording receiver), 278-279, 
287, 299 

Beechnut (ideograph transmission 
system), 198, 399 
Big Ben, 300 

Boozer (radar warning receiver), 206, 
287, 299 
Carpet II, 300 
Chaff, 230-231, 234-237 
Mandrel, 267 
Moonshine, 245, 266-267 
Perfectos (homing system), 295, 380 
Ping Pong (direction finder), 278, 304 
Tinsel (jamming modulation method), 
172 

Tuba, 140, 300-302, 390-391 
Window, 234-237 
Broad-band antenna system, 442 
Broadloom (jamming transmitter), 386 
Broom (automatic search jammer), 
181-182, 393 

BTL 

see Bell Telephone Laboratories 
Butterfly circuits for oscillators, 428 

C-1 communications ferret, 150-151, 
456 

C-1906 azimuth homing system for di- 
rection finders, 376 


524 


INDEX 


Cable, coaxial 
see Coaxial cable 
Cable, low-reflectivity, 140-141 
Calorimetric wattmeter, high-frequen- 
cy, 418-419 

coaxial line sections, 75 
microwave wattmeter, 419 
water-load type, 419 
CAOS-50 AEY filter (antijamming 
video filter), 405 

Carbon granules as noise source, 27 
Carpet (jamming transmitter), 275-284, 
289-292, 385-387 
automatic searching, 290, 387 
barrage jamming, 275, 345-346 
discriminator circuit, 300 
history of operational use, 279-284, 
290 

limitations, 276-277 
modifications permitting 335- to 415- 
mc operation, 389 

performance as spot jammer, 275, 
280, 385, 457 

use as radar operator training aid, 79 
Carpet checker, 418 
Carpet output indicator, 418 
Carpet tester, 414 

Cathode-ray tubes with long afterglow, 
407 

CBS (Columbia Broadcasting System) 
pulse generator, 415 
radar jamming transmitters, 214-229 
radar receiving and direction-finding 
equipment, 203-213 
radio countermeasures, test methods 
and equipment, 66-75 
Chaff (confusion reflector), 231-237, 
408-410 

aluminum foil, 231, 235, 409 
birdnesting, 231 
cutting machine, 231-233 
design considerations. 111 
determination of induced current, 
111-113 

dispensers, 410 

effectiveness, 273-275, 409, 431 
frequency range, 233 
number and length of dipoles, 233- 
234 

production methods, 409 
response, 113, 409-410 
special Chaff bombs, 283 
specifications, 231, 408, 410 
types, 232-233 

unit of Chaff, definition, 233-234 
Chaff, flat, 230-231, 234-237 
comparison with bent Chaff, 234-236 
effect of humidity, 236 
frequency range, 234-236 
German type, 236-237 
length, 236 


Chick (expendable jammer), 174-175, 
215-216, 391-392 
evaluation, 140 
parachute-borne, 140, 172 
performance, 175 
spark type, 392 

Cigar (communications jammer) 
effectiveness, 140, 400 
modifications for spot jamming, 389 
type of oscillation, 175-176 
Cinaudagraph Corporation, miniature 
gas triodes, 23-24 
Circuits, electronic 

amplifier back-biasing circuit for 
antijamming, 252 

butterfly circuit for u-h-f oscillators, 
428 

pass circuit for pulse receivers, 191 
Silent Knight, 373 

Clipping, effect on noise spectra, 84-88 
advantages, 85-87 
definition of clipping, 84 
dependence upon bandwidth, 255 
Dina noise, 85, 88 
effectiveness for jamming, 88, 431 
gas tubes, 102, 450 
noise-modulated carrier, 88 
random noise, 164 
rectifiers, 102 

spectral distribution, 81, 84-87, 102 
CLU-24314 antenna selection switch, 

445 

Coastal-watch radar, jamming sus- 
ceptibility, 13 
Coaxial cable, 445-447 
antenna, 445 

bandwidths of resonant-line sections, 

446 

cavity oscillator, 425-426, 428 
effect of copper losses, 446 
Federal B-45; 446 
filters, 453 

impedance of shielded balanced line, 
446 

line oscillator, 428 

mode separation in coaxial oscillator, 
446 

RG-21/AU cable, 446 
velocity of propagation, 132 
wide-band coaxial lines, 446 
Code systems, 197-200 
antijamming printing attachment, 
198-200 

Beechnut, 198, 399 
teleprinters, 197 
Voflag, 198, 399 

Cold-cathode tubes for noise jamming, 
29, 451 

Columbia Broadcasting System 
pulse generator, 415 
radar jamming transmitters, 214-229 



radar receiving and direction-finding 
equipment, 203-213 
radio countermeasures, test methods 
and equipment, 66-75 
Communications ferrets, 149-151 
C-1 ferret, 150-151, 456 
installation, 458 
recommendations, 150 
requirements, 149-150 
Communications jammers, 169-179, 
381-383 

Chick, 172, 174-175, 215-216, 391-392 
Cigar, 140, 175-176, 389, 400 
comparison with radar jammers, 215 
design considerations, 215 
Dina, 85-88, 222-225, 381-382 
effectiveness, 165-167, 401 
ferrets, 149-151, 456, 458 
general jamming problem, 160-162 
394 

interference generator, 381 
Jackal jammer, 383, 395, 456, 458 
Jostle IV; 456 

monitoring and tracking victim sig- 
nal, 394 

Pad, 174, 381-382 
spark jammers, 171-172, 382, 392 
Communications search receivers, 371 
Communications systems, antijamming 
characteristics, 188-191, 398-401 
Beechnut, 399 
comparison of systems, 190 
facsimile transmission system, 398-399 
f-m receivers, 397-398, 400-402 
personnel training, 189 
protected communication system, 400 
pulse communications, 191, 398 
radio-printing systems, 197-200, 399 
telegraphy, 190, 197, 399-400 
Communications systems, jamming 
vulnerability, 191-195 
a-m receivers, 193, 395, 397 
facsimile and teletype systems, 194, 
401 

f-m receivers, 193-194, 395, 396 
pulse systems, 194-195 
recommendations, 195 
telegraph systems, 393, 395, 397 
to c-w and a-m signals, 193 
233 A airborne transceiver, 401 
Cone antennas 

AS-44/APR-5; 434 
bandwidth, 439 
double-cone assembly, 434 
radiation patterns, 441 
Confuser, mechanical (noise generator), 
26-27 

Confusion devices 

see Deception and confusion devices 
Constriction oscillators as noise jam- 
ming source, 25, 451 


INDEX 


525 


Continuous wave for jamming, effec- 
tiveness, 164-165, 193, 400 
Continuous wave magnetrons 
A- 131; 425 
1-kw, 425 

self-regulating field excitation, 429 
tantalum cylinder cathodes, 425 
Continuous wave modulation, 164-165, 
193, 400 

Controlled-device jammers, 380-381, 
392-393 

Corner reflectors (radar deception de- 
vice), 241-244 
aircraft-towed, 243 
Angels, 116-117, 230-231, 241-243, 
411-412 

balloon-supported, 242-243 
effective echoing area, 241 
effects of diffraction, 116-117 
for protection from flak, 459 
ground-based, 244 
naval Spoofs, 459-460 
raft-or-boat-supported, 243 
types, 241 

Corny (tuning of multianode magne- 
trons), 47 

Crystal mixers for spectrum analyzers, 
72, 416 

Crystal rectifier voltmeter, 420 
Crystals for noise jamming source, 28 
Curtain (homing device), 295, 379- 
380 

CV-9/APT transmitter output indica- 
tor, 418 

CV172 diode as noise source, 29 
C-w jamming, effectiveness, 164-165, 
193, 195, 400 
C-w magnetrons 
A-131; 40, 43, 425 
1-kw, 424, 425 

self-regulating field excitation, 429 
tantalum cylinder cathodes, 425 
C-w modulation, 164-165, 193, 400 
C-w oscillators, 425-426 
GE-L-3 triode, 426 
GE ZP-449 triode, 426 
microwave, 426 
ZP-522 triode, 428 
C-w telegraphy, jamming of, 396 
CXCE (radar jammer), 384 
Cylindrical antennas 

impedance characteristics, 439, 445 
theoretical study, 123 
Cylindrical magnetrons, 429 

D-1905 spurious response indicator, 
radar, 372 

D-9000 search receiver, 208-213 
D 159076 photomultiplier tube, 20 
DBA direction finder, 379 
DBM direction finder, 378-379 


Deception and confusion devices, 408- 
413 

Angel, 116-117, 241-243, 411-412 
blanket masking signal system, 152- 
153, 412 

Chaff, 111-113, 231-237, 273-275, 
408-410 

corner reflectors, 116-117, 241-244, 
411-412, 459 

direction-finding deception systems, 

412 

Elmer, 309, 413 
Fishline, 238 
mechanical, 26-27 
Moonshine, 245, 266-267 
Peter, 245-247, 306, 412-413 
pulse transmitters, 247-248 
Rope, 113-115, 237-240, 363-365, 
410 

Stardust pulse repeater, 412 
summary of development work, 423- 
424 

Turnstile, 230-231, 238-239 
use of enemy frequency, 247-248 
Deflection modulation, effect on screen 
brightness, 98-99 
DF (direction finders) 
see Direction finders 
Differential analyzer, study of electron 
paths, 144-145 

Dina Chick (expendable jammer), 172, 
174-175, 215-216, 391-392 
evaluation, 140 
performance, 175 
spark type, 392 

Dina jammer (direct-noise amplifica- 
tion), 381-382, 384 
design considerations, 170, 218 
jamming effectiveness, 167, 430-431 
noise clipping, 85, 88 
use against guided missiles, 381 
use against SLC radar, 361-362 
Diode as noise source, 29 
Dipoles 

see Antennas; Direction finders; Win- 
dow 

Direct-detection search receivers, 208 
Direction finders, 11, 375-380 
see also Antennas; Homing devices 
and attachments 
against radar, 207, 210-212 
airborne, 300-1000 me, 377 
AN/APA-17; 288, 457 
antenna spinner system, 377-378 
antennas, 375, 422, 440, 455-456 
comparison with homing system, 
206-213 

countermeasures to, 151-153, 412, 

413 

DBA, 379 
DBM, 378-379 


Judy, 380 
NLS-694; 151 
Ping Pong, 278, 304 
setter (attachment for frequency 
range), 375-376 
ship-borne, 300-1000 me, 378 
spinning loop, 380 
submarine system, 379 
trainers, 79, 422 

Directivity patterns of antennas 
see Antennas, radiation patterns 
Direct-noise amplification (Dina), 381- 
382, 384 

design considerations, 170, 218 
jamming effectiveness, 167, 430-431 
noise clipping, 85, 88 
use against guided missiles, 381 
Donutron tubes (internally-tuned), 426- 
427 

E-409 remote-tuning transmitter at- 
tachment, 260 

E-410 antijamming filter, 260 
E-411 gang tuning radar attachment, 
260 

E-413 remote-tuning transmitter at- 
tachment, 260 

E-510 high-pass antijamming filter, 259 
E-512 oscillator detuning attachment 
for antijamming, 259 
E-515 high-pass antijamming filter, 
259 

E-1601/1602 detector and video units 
for antijamming, 259 
E-1610 high-pass antijamming filter, 
259 

Early-warning radar, countermeasures 
to, 359-360 

deception devices, 349-350 
jamming, 13, 458 
Rope, 359 

Early-warning receivers 
see Warning receivers 
Echoes 

from shell bursts, 245 
means of distinguishing real from 
artificial, 406-407, 459-460 
radar, 128-129, 143-144, 458 
ships, 128-129 

860 me tetrode resnatron, 52 
884 gas tube, use as noise source, 22, 
449, 450 

Electra (German bomber navigational 
aid), 264 

Electron tube development, 39-53 
5-kw triode for 70- to 350-mc range, 
423-424 
flute tubes, 45 

L-14 tunable broad-band amplifier, 
423 

local oscillator, 425 


526 


INDEX 


magnetrons, 39-44, 136, 144-145, 422- 
428 

resnatrons, 51-53, 422, 428-429 
techniques in tracing electron paths, 
423 

ultra-high-frequency diode, 422 
Elephant (ship-borne jamming sys- 
tem), 228-229, 253-254, 300, 390- 
391 

Elmer (communications deception de- 
vice), 309, 413 

End-fed balanced antennas, 437-438 
Enemy radar 

see Japanese radar 
Enemy research 

see German research 
E\V radar (early-warning), counter- 
measures to, 359-360 
deception devices, 349-350 
jamming, 13, 458 
Rope, 359 

Expendable jammer (Chick), 172, 174- 
175, 215-216, 391-392 
evaluation, 11, 140 
performance, 175 
spark type, 392 

F-2306 Carpet output indicator, 418 
Facsimile transmission system 

antijamming characteristics, 398-399 
vulnerability to jamming, 194 
Fan antennas, impedance character- 
istics, 445 

Fanny (homing attachment for direc- 
tion finders), 376 
ED radar (fire-control) 

antijamming attachments, 259, 405 
range indicator, 406 
susceptibility to jamming, 257 
Federal B-45 coaxial cable, 446 
Federal Telecommunication Labora- 
tories, Inc. 

jamming and antijamming tech- 
niques, 188-200 

jamming transmitters, 160-187 
nonradar receiving and direction- 
finding techniques, 149-159 
vacuum-tube development, 39-53 
Federal Telephone and Radio Cor- 
poration, sealed-off resnatron, 
52-53 

Ferrets for searching and monitoring 
communications systems 
C-1 ferret, 150-151, 456 
installation, 458 
recommendations, 150 
requirements, 149-151 
FGlOl German radio altimeter, 140 
FG178A thyratron, noise output, 449 
15-kw ground jammer (Cigar) 
effectiveness, 140, 400 


modifications for spot jamming, 389 
type of oscillation, 175-176 
Fighter planes, countermeasures to, 
293-295 

Beaver III; 284 

communications interference, 271- 
273 

Curtain, 295 
Perfectos, 295 
radar interference, 272 
radar screens, 294-295 
Filters, 134-135 
band-pass, 453 
coaxial filters, 135, 453 
general properties, 135 
microwave, 453 
75-mc low-pass filter, 452 
u-h-f, 452, 453 
Filters for antijamming 
E-410; 260 
E-510; 259 
E-515; 259 
E-1610; 259 
high-pass filter, 405 
RC filter, 252 
RFC filter, 252 
video filter, 405 
Fire-control radar 

Mark IV; 257, 259, 405, 406 
Mark 8; 403 
SCR-545; 257, 404 
Fishhook antenna, 296-297, 436 
Fishline (radar deception device), 238 
5J21 (ZP-612) magnetron 
cathode, 48 
characteristics, 44 

response to noise modulation, 427- 
428 

tuning method, 48 
wave-guide transformer, 46, 49 
5J29 (ZP-579) magnetron 
characteristics, 40, 43 
design and performance, 422 
efficiency, 423 
5J30 (ZP-590) magnetron 
characteristics, 40 
electron escape, 42 
frequency range, 43, 45 
5J31 (ZP-584) magnetron, 40, 43 
5J32 (ZP-646) magnetron 
characteristics, 40, 43 
electron escape, 42 
5J33 (ZP-676) magnetron, 40, 43, 45 
Flak, radar-controlled, countermeas- 
ures to, 269-271, 279-284, 289- 
293 

aircraft flying formation, 270 
Carpet, 279-282, 289-292 
Chaff, 282-284, 292-293 
corner reflectors, 459 
evasive action, 270 


Flute tubes, 45 

F-m adapter, use in receivers, 190, 
398 

F-m altimeters, vulnerability to jam- 
ming, 196-197, 413 
F-m communications systems 

antijamming characteristics, 397,400- 
402 

crystal-controlled, 395 
vulnerability to c-w jamming, 193- 
194, 400 

vulnerability to f-m barrage jam- 
ming, 396 
F-m jamming 

see Frequency-modulated jamming 
F-m oscillators for panoramic reception, 
371 
Formulas 

current distribution induced in Chaff, 
111-113 

energy density of pulsed signals, 84 
modulation index, 81 
noise current at cathode photocell, 19 
output spectrum for a-m by noise, 81 
output spectrum for f-m by a sine 
wave, 81 

output spectrum for f-m by noise, 81 
output spectrum for simultaneous 
f-m and a-m, 82-84 
output spectrum for simultaneous 
f-m by noise and sine wave, 82 
plasma-ion oscillation for gas-dis- 
charge tubes, 21 

radial motion of the electron in 
magnetrons, 136 

rate of ion production in gas tubes, 
101 

sawtooth frequency modulation, 106- 
107 

sinusoidal frequency modulation, 105 
spectral distribution of clipped noise 
wave, 84 

square-wave frequency modulation, 
107 

triangular frequency modulation, 107 
Frequency meters 
accuracy, 204 

bandwidth adjustment indicator, 417 
BC-1255A, 417 

heterodyne frequency meter, 417 
methods for pretuning jammers, 418 
portable battery-operated, 417 
wavemeter, 417-418 
Frequency modulator, type P-550; 67 
Frequency multiplier, P-554; 68 
Frequency- modulated altimeters, jam- 
ming vulnerability, 196-197, 413 
Frequency-modulated communications 
systems 

antijamming characteristics, 397,400- 
402 


INDEX 


527 


crystal-controlled, 395 
vulnerability to c-w jamming, 193- 
194, 400 

vulnerability to f-m barrage jam- 
ming, 396 

Frequency- modulated jamming, 104- 
110, 162 

applications, 430-432 
barrage jamming, 382, 396 
by noise, 81-82, 394 
effectiveness, 163, 393-394, 396, 429 
electromechanical method, 170 
electronic method, 169-170 
Jackal jammer, 383, 395, 456, 458 
jittered f-m, 108-109, 396, 432 
pulses, 398 

requirements, 107-108 
sawtooth, 106-107 

simultaneous f-m and a-m, 82-84, 109 

sinusoidal, 81-84, 105 

spot jamming, 387 

square-wave, 107 

transmitter design, 169-170 

triangular, 107 

types, 108 

variation of coil inductance, 170 
Frequency- modulated oscillators for 
panoramic reception, 371 

Gas tube noise sources for jamming, 
21-25, 449-452 
2C4 gas triode, 449 
2D21; 450 

6D4 gas tube, 23-25, 102, 423, 449- 
451 

2050 gas tube, 450 
audio noise sources, 21-22 
clipping, 102 
cold-cathode, 29, 451 
FG178A thyratron, 449 
hot-cathode, 451 

in magnetic fields, 24-25, 101-102 
plasma region, 21, 101 
rate of ion production, 101 
video noise sources, 23-25 
Gaston (audio noise generator), 22, 175 
GCI radar (ground-controlled inter- 
ception) 

jamming of, 12, 140 
warning receiver, 1 1 
GE ZP-449 c-w oscillator, 426 
General Electric Company 
c-w oscillators, 425-426 
differential analyzer, 144-145 
limitations of magnetrons, 42-43 
neutrode magnetron, 43 
noise jamming sources, 19-38 
1-kw magnetrons, 44-50 
radar deception, 230-248 
radio countermeasures, test methods 
and equipment, 66-75 


6D4 noise unit, 24-25 
spectrum analyzers, 68-74 
TDY radar jamming transmitter, 214 
vacuum tube development, 39-53 
General Radio Company 

radio countermeasures, test methods 
and equipment, 66-75 
sound analyzer, 30 
TPQ-T2 signal generator, 261-262, 
421 

German research 

Big Ben (V-2 rocket), 300 
bomber navigational aids, 264 
control mechanism of BlVb tank, 
413 

flat Chaff, 236-237 
Hs-293 glider bomb, 65, 195-196, 445 
radar, 234, 297-299, 457, 460 
radio altimeters, 140, 196-197, 454- 
455 

Germanium crystals, use as modula- 
tors, 72 

GL-522 oscillator, use as a third- 
harmonic generator, 429 
GL radar (gun-laying), countermeas- 
ures to, 360-365 

Carpet, 275-282, 289-292, 385-387 
Chaff, 111-113, 231-237, 273-275, 
408-410 

effectiveness, 350-352 
operational problems, 360-361 
requirements, 12 

Rope, 113-115, 237, 240, 363-365, 410 
GL radar (gun-laying), warning re- 
ceiver, 11 

Glide bombs, countermeasures to 
see Guided missiles, countermeasures 
to 

GM jammers 

see Guided missiles, countermeasures 
to 

Gold-copper alloy solder, 145, 423 
GR (General Radio Company) 

radio countermeasures, test methods 
and equipment, 66-75 
sound analyzer, 30-31 
TPQ-T2 signal generator, 261-262, 
421 

Ground forces, use of radio counter- 
measures, 309-310, 367-368 
Ground-based antennas, 58-60 
bandwidth, 55 
directivity, 55-56 
for AN/GRQ-1 jammer, 64 
models, 143 

use against AI and GCI radar, 55-56 
wave antenna, 64 
Ground-based jammers, 180-183 
advantages, 11 

AN/GRQ-1; 64, 180-181, 393 
Beagle, 182 


Beaver III; 284 
Broom, 181-182, 393 
Cigar, 140, 175-176, 389, 400 
disadvantages, 215 
Elephant, 228-229, 253-254, 300, 390- 
391 

Piano, 182-183 
Tuba, 140, 300-302, 390-391 
Ground-controlled interception radar 
jamming of, 12, 140 
warning receiver, 1 1 
Guided missiles, countermeasures to, 

179- 189 

airborne jammers, 183-184 
AN/GRQ-1 jamming equipment, 64, 

180- 181, 393 

AN/SRQ-1 multi-channel jammer, 
186-189, 392 

automatic search jammers, 181-182, 
393 

Dina, 381-382 

effect of reflected radar waves, 380 
effectiveness, 195-196, 303 
MAS ship-borne jammers, 185-186, 
392-393 

1.5-kw airborne jammer, 392 
Peter Pan jamming system, 155-159, 
381 

Piano, 182-183 
ship-borne jammers, 185-187 
specifications for jammers, 180 
Gun-laying radar, countermeasures to 
see GL radar (gun-laying), counter- 
measures to 

Gun-laying radar, warning receiver, 1 1 


HlOO video spectrum analyzer, 30 
H205 peak reading voltmeter, 31 
H206 tube tester, 31 
H300 video spectrum checker, 30 
H500 audio spectrum analyzer, 30 
Hallicrafter S-27D search receiver, 371 
Harvard University 

see Radio Research Laboratory 
Hen (expendable transmitter for propa- 
ganda broadcasting), 398 
Heterodyne frequency meter, 417 
Hewlett-Packard wave analyzer, 31 
Hipersil transformer cores, 33 
History of operational use, 264-310 
air forces, 269-277 
British, 264-267, 299-302 
civilian aid, 268-269, 277-278, 299- 
300 

European Theatre, 287-299 
ground forces, 309-310, 367-368 
Mediterranean Theatre, 277-287 
naval operations, 302-309 
Normandy invasion, 457 
Pacific Theatre, 311-368 


528 


INDEX 


Homing devices and attachments, 376- 
377 

applications, 207 
aural or visual indication, 378 
C-1906 azimuth homing system, 376 
comparison with direction finders, 
206-207, 213 
Curtain, 295, 379-380 
Fanny, 376 
limitations, 207 
Moth, 379, 442-443 
Perfectos, 295, 380 
radar homing bomb, 257, 404 
Tail, 376 

types used against radar, 206-207, 
210, 213 
v-h-f, 377 

Horn-type antenna, 436 
Hs-293 glider bomb 
antenna patterns, 65, 445 
jamming vulnerability, 195-196 

Ideograph transmission system (Beech- 
nut), 198, 399 

Ignoramus theory, search receivers, 
138-139 

Impulse and time code systems 
Beechnut, 198, 399 
Voflag, 198, 399 

Intensity modulation, effect on screen 
brightness, 98-99 

Interference generators, 261-262, 381, 
421, 422 

Jackal (f-m barrage jammer) 
AN/ARQ-2; 395 
AN/ART-3; 383, 456 
effectiveness, 395 
installation in aircraft, 458 
Jammers 

see also Corner reflectors; Window 
airborne, 150-151, 183-184, 222-225, 
392 

alignment units for, 178-179, 394 
amplifiers for, 176-177, 382-383 
automatic, 181-182, 220-221, 226- 
228, 388-389 

design requirements, 173 
expendable, 172, 174-175, 215-216, 

391- 392 

ground-based, 175-176, 180-183, 284, 
389 

of communications, 85-88, 149-151, 
160-179, 381-383 

of controlled devices, 13, 380-381, 

392- 393 

of guided missiles, 155-159, 179-187, 
195-196, 380-382 

of radar, 172-175, 214-229, 383-392, 
457-458 

practice sets, 403, 415, 421-422 


pulse, 174, 381-382 
ship-borne, 185-187, 228-229, 390-393 
signal-repeating, 155-159, 182-183 
step-tone, 401 
summary of types, 11-13 

Jammers, design considerations, 169- 
173, 214-222 

amplitude-modulation methods, 170- 
172 

barrage versus spot jamming, 216 
communications versus radar jam- 
mers, 215 

conversion of communications trans- 
mitters, 172 

enemy equipment, 214-215 
expendable, 172 
frequency setting, 219-222 
frequency-modulation methods, 169- 
170 

listening-through systems, 173 
minimum effective distance, 218-219 
power requirements, 218-219 
sideband energy distribution, 217-218 
spot jamming, 216 
tactical considerations, 221-222 
types, 216-217 

Jamming, countermeasures to • 
see Antijamming techniques 

Jamming, theoretical studies, 80-146 
effectiveness calculations, 140-141 
frequency modulation, 104-110 
noise studies, 80-104 
transmission and reflection of energy, 
110-135 

Jamming methods 

a-m, 81-84, 170-172, 193, 429-432 
audio waveform requirements, 162 
barrage jamming, 168-169, 174-176, 
216-217, 381-383 

c-w modulation, 164-165, 193, 400 
f-m, 81-84, 104-110, 393-394, 456-458 
noise, 19-38, 80-99, 163-165, 448-452 
periodic jamming, 255-256 
pulse modulation, 171, 174, 381-382, 
398 

qualitative comparison of types, 82 
random jamming, 255-256 
selection of type, 165, 216-218 
sine-wave modulation, 165 
spot jamming, 168-169, 176-179, 275- 
276, 384-387 

Jamming methods, effectiveness 
a-m, 255-256, 430-432 
barrage jamming, 168, 276, 383 
c-w modulation, 164-165, 193, 195,400 
dependent factors, 161, 395 
effect of receiver bandwidth, 256 
field tests, 383 

f-m, 81-84, 393-394, 396, 429-430 
from defensive aspect, 256 
from offensive aspect, 255-256 


J/S ratio, definition, 255 
method of measuring, 140-141, 461 
noise, 88, 255-256, 431 
periodic jamming, 256 
power requirements, 167 
pulse modulation, 430, 432 
radio waveform requirements, 1 62- 1 63 
spectrum of most effective type, 393- 
394 

speech-masking effectiveness, 393 
spot jamming, 168 
Jamming sets for training, 420-422 
100-350 me, 421 
175-550 me, 420 
450-720 me, 420-421 
450-1000 me, 422 
L-105; 403 

Jamming susceptibility 
blind bombing, 404 
bombsights, 197 

communication systems, 191-195, 

393-398, 401 

German Hs-293 glider bomb, 195-196 
J apanese communications equipment, 
396-397, 402-403 
Loran navigational system, 395 
radar, 12-13,257-258,403-404,429-431 
radio altimeters, 140, 196-197, 413 
radio telegraphy, 393, 395, 397 
receivers, 166, 193-195, 400-403 
test equipment, 66-68 
Jansky and Bailey, jamming and anti- 
jamming techniques, 188-200 
Japanese communication equipment, 
jamming susceptibility, 396-397, 
402, 403 

Japanese direction finders, counter- 
measures to, 151-152, 413 
Japanese radar 

airborne, 311, 334-342 
allied reconnaissance during World 
War H; 277-279, 287-289, 317- 
325, 346-349, 354-359 
characteristics, 458 
GL and SLC radar, 313 
ground radar, 333 
Mark I; 333 
Mark VI; 334-335 
Mark B, 333 
ship-based, 312-313 
surface radar, 325-334 
Jostle IV (barrage jammer), 456 
J/S ration (jammingtosignal power), 255 
Judy (instantaneous direction-finding 
system), 380 

Kites 

see Angels (corner reflector) 

Klystron, reflex, 68-69, 71 
Knickebein (German bomber naviga- 
tional aid), 264 


INDEX 


529 


L-14 parallel-plane triode 
application, 41-42 
characteristics, 40 
design, 423 

L-104 multianode magnetron 
characteristics, 44 
design, 424 
tuning method, 47-50 
L-105 jamming signal generator, effec- 
tiveness, 403 

L-901 video unit for antijamming, 259 
LC, tuning of multianode magnetrons, 
47-48 

Listening-through radio jamming, 173, 
177-178 

Litton Engineering Laboratories, vac- 
uum tube development, 39-53 
Lobe-switching antennas, 439-440 
Local oscillators, 40-41, 425 
Long-wire antennas, 443 
Loop antennas 
circle, 125-126 

equations describing features, 440 
radiation patterns, 125-126, 443-444 
rhombus, 126 
square, 126 

techniques of modeling, 375 
Loran navigational system, vulnerabil- 
ity to jamming, 395 

Magnetic audio noise generators. 22 
Magnetic tape recorders, 155-158 
AN/ARQ-12; 156-158, 380 
AN/SRQ-2; 156-158, 380 
use in Peter Pan jamming system, 
155-157, 381 
vicalloy tape, 157 
XN-1; 156-158 
Magnetrons, 39-51, 422-428 
characteristics, 40 
c-w, 40, 43, 425, 429 
cylindrical, 429 
design of electromagnets, 424 
donutron, 426-427 
filament regulator, 144, 423 
flute tubes, 45 
for jamming, 225, 387-388 
high-power, 50 
limitations, 42-43 
medium-power, 42-44 
method for “cold” testing, 424 
modulation, 427-428 
1-kw, 44-50, 424-425 
Piccolo, 44, 49-50, 424 
scaling formula for new designs, 425 
specifications, 44-45 
Squirrel-Cage, 39-41, 426-427 
summary of development work, 423- 
424 

theoretical studies, 136, 144-145 
waveguide output magnetrons, 425 


Magnetrons, multianode, 45-50 
A- 132; 44-45 
A- 133; 44-45 
C- and L-rings, 47-48 
cathode, 48-49 
characteristics, 44 
diode cutout, 50 
L-104; 44, 47-50, 424 
magnetic field design, 46 
output, 46 
Piccolo tubes, 49-50 
radial-vane type, 46 
612 L, 44 

suggested improvements, 50 

tuning methods, 46-48 

use of mumbo, 46-47 

ZP-594; 44, 49, 424 

ZP-595; 50-51, 422 

ZP-597; 44, 49, 424, 427 

ZP-612 (5J21); 44, 46-50, 427-428 

ZP-615; 44, 49 

ZP-616; 44, 48, 49, 424 

ZP-639; 44, 49 

Z P-693; 44 

ZP-838; 44 

Magnetrons, neutrode 
characteristics, 40, 44 
ZP-647; 43-45 
ZP-675; 40, 43 
ZP-676; 40, 43, 45 
ZP-677; 43 
ZP-685; 43-45 
Magnetrons, split-anode 
characteristics, 40, 44, 51 
limitations, 42-43 
recommendations, 43 
types, 43 

ZP-579; 40, 43, 422-423 

ZP-584; 40, 43 

ZP-590; 40, 42-43, 45 ^ 

ZP-595; 50-51, 422 
ZP-599; 44-45 
ZP-633; 40, 43, 423 
ZP-636; 50-51, 423 
ZP-646; 40, 42-43 
ZP-666; 40, 43 
Magnetrons, tunable 
A-131; 40, 43, 425 
radar jammers, 387-388 
6J21; 425, 428 

Mandrel (barrage jammer), 267, 383 
Mark I (Japanese) radar, 333 
Mark IV radar 

antijamming modifications, 259, 405 
range indicator, 406 
susceptibility to jamming, 257 
Mark 4E (Japanese transmitter-receiv- 
er), jamming vulnerability, 402 
Mark VI (Japanese) radar, 334-335 
Mark 8 radar, antijamming character- 
istics, 403 


Mark 31 (radar-controlled missile), 
jamming vulnerability, 257, 404 
Mark B (Japanese) radar, 333 
MAS ship-borne jammer, 185-186, 392- 
393 

Masking signal system for radio com- 
munication, 412 

Massachusetts Institute of Technology, 
antijamming research and de- 
velopment, 249-260 
Mechanical noise generators, 25-28 
carbon granules, 27 
confuser, 26-27 
rotary spark-gap, 28 
speed-x buzzer, 28 
Meter detection of radar signals 
aperiodic meter, 95 
evaluation, 431-432 
periodic meter, 95 
pulse length, 95 
sensitivity, 95 
Meters, frequency 
see Frequency meters 
Microwave c-w power oscillators, 426 
Microwave filters 
design, 453 

insertion loss, measuring techniques, 
453 

Microwave radar, countermeasure to 
see Angels (corner reflector) 
Microwave search receivers, 288, 420 
Microwave wattmeter, 419 
Mine detonator, jamming vulnerability, 
195, 402 

Missiles, self-guided 
see Guided missiles, countermeasures 
to 

MIT, antijamming research and de- 
velopment, 249-260 
Modulation index 
formula, 81 
limits, 82, 108 
Modulations for jamming 
see Jamming methods 
Monimax transformer cores, 33, 36-37 
Moonshine (pulse-repeating system), 
245, 266-267 

Moth (self-guided homing missile), 379, 
442-443 

Multianode magnetrons 
see Magnetrons, multianode 
Mumbo (tuning of multianode magne- 
trons), 46-47 


Naval Research Laboratory, blanket 
antenna, 153 

Naval Spoofs (seaborne corner reflec- 
tors), 459-460 

Naval Training School, Fort Lauder- 
dale, Florida, 261 


530 


INDEX 


Navigational aids for bombers 
countermeasures to, 151, 413 
types, 264 

Neutrode magnetrons 
characteristics, 40, 44 
ZP-676; 40, 43, 45 

Nickel-silicon-iron alloy transformer 
cores, 33 

931 photomultiplier, 19-20 

frequency spectrum, 99-101, 448 
life tests, 448 
noise spectrum, 20 
operating characteristics, 448 
tube tester, 31 

NLS-694 aircraft direction finder, 
151 

Noise, effect on signal visibility 
see Signal visibility through noise 
Noise, jamming methods, 80-99 
clipped, 84-88, 102, 431, 450 
effectiveness, 91-99 
modulated, 80-84, 163-165, 255-256 
rectified, 88-93, 450 
Noise analyzer, 420 
Noise generators 

see also Gas tube noise sources for 
jamming 

audio, 21-22, 175, 451-452 
for static burst jamming, 397 
magnetic, 22 
mechanical, 25-28 
P-551; 67 
video, 23-25, 451 
voice-frequency, 451 
Noise modulations for jamming, 80-84 
advantages, 163-164, 217 
a-m by noise, 81-84 
clipped noise, 164, 255-256 
disadvantages, 164 
effectiveness, 88, 255-256, 431 
f-m by noise, 81-82, 394 
of communications, 163-165, 398 
random noise, 163-165 
thermal noise, 163-164 
Noise sources for jamming, 19-38, 448- 
452 

constriction oscillator, 25, 451 
gas tubes, 21-25, 101-102, 449-452 
moving arc, 29 
noise generators, 25-28, 451 
photoelectric noise, 19-21, 99-101, 
448, 452 

semiconductors and crystals, 28 
specifications for satisfactory sources, 
19 

summary of development work, 423- 
424 

transformers, 32-38, 102-104 
Tungar bulbs, 452 
Noise spectra, effect of clipping 

see Clipping, effect on noise spectra 


Noise transformers, video, 32-38 
core losses, 34 
core materials, 33 
design, 36-38, 454 
impedance measurements, 33 
tests, 37-38 

Noise tube tester, 31, 419-420 
Noise-measuring techniques, 29-32 
audio spectrum analyzers, 30-31 
equalization of noise, 31-32 
theoretical analysis of noise, 29-30 
tube testers, 31, 419-420 
video spectrum analyzers, 30, 416 
Noise-measuring voltmeter, 31, 451 
Noise-modulated carrier, effect of clip- 
ping, 88 

Noise-modulated jammer (Mandrel), 
267, 383-384 

NRL (Naval Research Laboratory), 
blanket antenna, 153 


OCC spectrum analyzer, 68-70 
Officer training, radar antijamming 
techniques, 261 
Ohio State University 

antennas and power transmission for 
nonradar countermeasures, 54- 
65 

radar cross sections of aircraft, 130- 
131 

Oilcan tube, 41 
1.5-kw airborne jammer, 392 
158J (u-h-f diode), 422 
Oscillators 
audio, 414 
constriction, 451 

detuning attachment for antijam- 
ming, 253, 259 
f-m, 371 

local, 40-41, 425 

practice jammers, 261-262, 403, 415, 
420-422 

pulsed, 413-415 
r-f sweep generator, 414 
self-quenched, 174 
test oscillators, 67-68, 413-415 
Oscillators, ultra-high-frequency, 425- 
429 

butterfly circuit, 428 
coaxial cavity oscillator, 425, 428 
coaxial line oscillators, 428 
c-w oscillator, 425-426, 428 
magnetically-focused velocity-modu- 
lation tube, 426 
magnetrons, 426-429 
radial cavity oscillator, 429 
random-pulsed triode cavity oscilla- 
tor, 428 

resnatrons, 428-429 
third-harmonic generator, 429 


P-519 test oscillator, 67 
P-523-A test oscillator, 415 
P-525-A oscillator, 415 
P-550 frequency modulator, 67 
P-551 noise generator, 67 
P-552 test oscillator, 67 
P-553 test oscillator, 68 
P-554 frequency multiplier, 68 
Pad (noncoherent-pulse jammer), 381- 
382 

modulation, 174 
requirements, 174 
self-quenched oscillator, 174 
use against walkie-talkies, 382 
Panoramic Radio Corporation, non- 
radar receiving and direction- 
finding techniques, 149-159 
Panoramic search receivers, 153-155 
advantages, 204-205 
electronic tuning, 153-154, 371 
f-m oscillators, 371 
Panther, 154-155 
37- to 43-mc, 371 

Panoramic spectrum analyzer, 415 
Panther (panoramic receiver), 154-155 
Parachute Chicks, applications, 140, 172 
Parallel-plane triodes and tetrodes, 39, 
41-42 

Pass circuit for pulse receivers, 191 
Perfectos (airborne radar system), 295, 
380 

Periodic jamming 

effectiveness against intensity-modu- 
lated scopes, 256 
types, 255 

Periodic meter, detection of radar 
signals, 95 

Permalloy-ribbon transformer cores, 33 
Personnel training, 77-79 
antijamming techniques, 14 
antijamming training set, 261-262, 
421 

communications operators, 189 
courses, 77-78, 261, 316-317 
direction-finding trainers, 79, 422 
films, 77, 261-262 

interference generators, 381, 421-422 
jamming signal generators, 261-262, 
403, 415, 420-422 

Navy SC radar for antijamming 
training, 422 

phonograph records of jamming sig- 
nals, 422 

practice jamming sets, 261-262, 420- 
421 

radar operator training aids, 79 
spot-jammer operator, 79, 276 
Peter (electrical pulse repeater), 245- 
247 

field tests, 247, 412-413, 457 
frequency range, 246 


INDEX 


531 


modulation procedures, 247 
procedures for confusing enemy ra- 
dar, 245-246 
purpose, 306 
use of L-14 tube, 41-42 
Peter Pan (signal-repeating jammer), 
155-159 

a-c bias method of recording, 156 
accessories, 159 

countermeasure for guided missiles, 
155 

production, 159 
recorders, 155-157, 381 
Phase-modulated jamming 
see Frequency-modulated jamming 
Photomultiplier tube, 19-20 
frequency spectrum, 99-101, 448 
life tests, 448 
noise spectrum, 20, 99-101 
operating characteristics, 448 
recommendations, 21 
tube tester, 31 

Piano (signal-repeating jammer), 182- 
183 

Piccolo magnetrons 
characteristics, 44 
multianode, 49 

1-kw tunable c-w magnetrons, 424 
Pimpernel (automatic jammer), 226, 
389 

Ping Pong (British direction finder), 
278, 304 

Plasma region of gas tubes, 21, 101 
Porcupines (B-29 with barrage-jam- 
ming installation), 362-363 
Portable spectrum analyzer, 73-74 
Power meter, u-h-f, 418 
Practice jamming sets, 420-422 
100-350 me, 421 
175-550 me, 420 
450-720 me, 420-421 
450-1000 me, 422 
AN/UPT-1; 261-262 
AN/UPT-T4, 261-262, 420 
L-105; 403 
X-band jammer, 415 
Printing systems, radio, 197-200 
antijamming attachment, 198-200 
antijamming characteristics, 399 
impulse and time code systems, 198 
teleprinters, 197 

Propagation studies, meteorological ob- 
servations, 146 

Proximity fuze, countermeasure to, 13, 
159 

Pulse analyzers 
AN/APA-11; 417 
use of audio oscillator, 414 
Pulse communications systems, anti- 
jamming techniques 
clipper stages, 191 


pass circuit, 191, 398 
tests, 398 

Pulse communications systems, identi- 
fication, 371 

Pulse communications systems, jam- 
ming susceptibility 
AN/TRC-5; 194-195, 399 
noise jamming, 398 
phase-modulation system, 191, 398 
susceptibility to resistance noise, 397 
tests, 191 

Pulse repeaters (deception devices) 
Moonshine, 245, 266-267 
Peter, 245-247, 306, 412-413, 457 
Stardust, 412 

Pulse search receiver, 371 

Pulse stretcher for radar search re- 
ceivers, 373 

Pulse transmitters for radar deception, 
247-248 

Pulsed oscillators, 413, 415 

Pulses, efficiency for jamming, 167 
advantages, 84 
against guided missiles, 195 
barrage jamming, 432 
f-m pulses, 398 
noncoherent pulses, 165, 171 
Pad, 174, 381-382 
tests, 402 

Quado (jamming frequency alignment 
indicator), 178-179, 394 

Quadratic rectifiers, 90 

Radar countermeasures, 203-213 
Angels, 241-243, 411-412 
Chaff, 111-113, 231-237, 273-275, 
408-410 

effectiveness, 353, 366-367 
homing and direction-finding sys- 
tems, 210-213 
Moonshine, 245, 266-267 
Peter, 245-247, 412-413, 457 
search receivers, 203-205, 208-213, 
371-374 

table of receiver types, 209-210 
warning receivers, 11, 205-206, 213, 
413 

Radar countermeasures, design consid- 
erations, 203-207 
analysis of enemy radar, 203-204 
analyzing and indicating equipment, 
204-205 

antennas, 58-63, 433 
automatic search receivers, 205, 374 
direction-finding systems, 207 
homing systems, 206-207 
sensitivity of radar search receivers, 
205 

test equipment, 76-77 
warning receivers, 205-206 


Radar deception and confusion devices 
see Deception and confusion devices 
Radar echoes 
artificial, 410 

from ship targets, 128-129, 458 
use of models for experiments, 143- 
144 

Radar homing bomb, jamming sus- 
ceptibility, 257, 404 
Radar jammers, 172-175, 214-229, 383- 
392, 457-458 

AN/ARQ-8; 179, 183, 222-225 
Broadloom, 386 

Carpet, 275-282, 289-292, 361-363, 
385 

Chicks, 172, 174-175, 215-216, 391- 
392 

comparison with communications 
jammers, 215 
CXCE, 384 

design considerations, 215 
Dina, 384 

effectiveness, 255-256, 431 
Elephant, 228-229, 253-254, 300, 390- 
391 

Mandrel, 267, 383 
Pimpernel, 226, 389 
Rug, 384-385, 457 
table of types, 222-225 
Tuba, 140, 300-302, 390-391 
tunable magnetron, 387-388 
Radar operator training aids, 79 
Radar propagation studies, meteorolog- 
ical observations, 146 
Radar reception through noise, 93-96 
aperiodic meter, 95 
aural perception, 94 
comparison of methods of presenta- 
tion, 95-96 
linear detection, 94 
meter detection of signals, 95, 431- 
432 

periodic meter, 95 
quadratic detection, 94 
quantitative expressions, 94-95 
sensitivity of indicating methods, 94 
signal-to-noise ratios, 93-94 
visual perception, 93-95, 431-432 
Radar reflections, 130-131 
Radar screens, 288, 294-295 
Radar search receivers, 208-213, 371- 
374 

1000-3100 me, 372-373 
3000-6000 me, 373-374 
AN/APR-5; 373 

autosearch airborne receiver, 205, 374 
blanking circuit, 373 
direct-detection receivers, 208 
pulse stretcher for increased sensitiv- 
ity, 373 

recording unit, 374 


532 


INDEX 


sensitivity, 205 

single signal receiver, 373-374 

Spud, 373 

tuning units, 208, 372-373 
types, 209-210 

use in analyzing enemy radar, 203- 
204 

Radar spurious response indicator, 372 
Radar system for practice jamming, 
429-430 

Radar systems, antijamming character- 
istics, 249-260, 403-408 
AN/APG-1 (autotracking gun-laying 
radar), 404 

AN/APQ-5B (blind bombing attach- 
ment), 404 

AN/APS-4 (search and interception), 
404 

AN/APS-19 (search and intercep- 
tion), 251 

AN/TPL-1 (searchlight-pointing ra- 
dar), 404 

ASB (detection of surface vessels), 
260, 405-407 

ASG (detection of surface vessels), 403 

Mark IV, 259, 405 

Mark 8 (fire-control), 403 

recommendations, 262-263 

SCR-268; 259 

SCR-296; 259 

SCR-521A, 403 

SCR-717B (detection of surface ves- 
sels), 259, 403, 406 
SCR-720A (night fighters), 404 
Radar systems, jamming susceptibility, 
257-258, 403-406, 429-431 
AI radar, 12, 461 
AN/APS-4 radar, 257, 404, 461 
ASB, 405-406 
ASV, 257 
coastal- watch, 13 
early-warning, 13 
gun-laying, 12, 404 
Mark IV, 257 
Mark 31; 404 
Mark XXXI, 257 

RHB (radar homing bomb), 257, 404 
SCR-268; 257, 403 
SCR-545 (fire-control radar), 257, 
404 

SCR-720A, 404 
searchlight-control, 12 
searchlight-pointing radar, 257, 404 
type A presentations, 430 
type B presentations, 430 
Radar video analyzer, 391 
Radar warning receivers 
see Warning receivers 
Radar-controlled flak, countermeasures 
to, 269-271, 279-284, 289-293 
aircraft flying formation, 270 


Carpet, 279-282, 289-292 
Chaff, 282-284, 292-293 
corner reflectors, 459 
effectiveness, 458 
evasive action, 270 
Radiation Laboratory 

antijamming research and develop- 
ment, 249-260 

Squirrel-Cage magnetron, 39-41 
Radiation patterns of antennas 
see Antennas, radiation patterns 
Radio altimeters 
AN/ARN-1; 196-197 
f-m, 413 

German, 140, 196-197, 454-455 
vulnerability to jamming, 140, 196- 
197, 413 

Radio Corporation of America 
antennas and power transmission for 
nonradar countermeasures, 54-65 
broad-band matching transformers, 
134 

ground- wave propagation, 127 
jamming and antijamming tech- 
niques, 188-200 
jamming transmitters, 160-187 
noise jamming sources, 19-38 
nonradar receiving and direction- 
finding techniques, 149-159 
photomultiplier tube, 20-21 
vacuum tube development, 39-53 
Radio countermeasures, history of oper- 
ational use 

see History of operational use 
Radio countermeasures, personnel train- 
ing 

see Personnel training 
Radio countermeasures, summary of 
volume, 1-5 

Radio countermeasures, test methods 
and equipment 

see Test methods and equipment 
Radio direction finders 
see Direction finders 
Radio Research Laboratory 

antennas and power transmission for 
radar countermeasures, 54-65 
antijamming research and develop- 
ment, 249-260 

noise jamming sources, 19-38 
portable spectrum analyzer, 73-74 
radar deception, 230-248 
radar jamming transmitters, 214-229 
radar receiving and direction-finding 
equipment, 203-213 
radio countermeasures, test methods 
and equipment, 66-75 
Squirrel-Cage magnetrons, 39-41 
theoretical studies of jamming, 80-146 
vacuum tube development, 39-53 
video spectrum analyzer, 30 


Radio telegraphy jamming 
c-w telegraphy, 396 
effect on operators, 190 
effectiveness, 393, 395, 397 
tests, 399-400 
types of interference, 190 
Radio waveform for communications 
jamming modulation, 162-163 
Radio waves, radiation and propaga- 
tion, 123-131 

analysis of ship echoes, 128-129 
antenna studies, 123-127 
ground-wave field intensity, 127 
propagation studies, 127-128 
radar reflections, 130-131 
recommendations, 128 
Radio-controlled devices, countermeas- 
ures to 

see Guided missiles, countermeasures 
to 

Radio-frequency power indicator, 418 
Radio-frequency sweep generator, 414 
Radio-frequency voltage regulator, 454 
Radio-navigation aids 

countermeasures to, 151, 413 
types, 264 

Radio-printing systems, 197-200 
antijamming characteristics, 399 
impulse and time code systems, 198 
teleprinters, 197 

Radio-printing systems, antijamming 
attachment, 198-200 
basic method, 198-199 
details of printer, 199-200 
effectiveness, 199 
printer signal, 198-199 
recommendations, 200 
Tuning Fork, 199-200 
Railing type modulation 

see Pulses, efficiency for jamming 
Random jamming, 255-256 
Random-pulsed triode cavity oscillator, 
428 

RC (resistance-capacitance) video filter 
for antijamming, 259 

RCA 

see Radio Corporation of America 
RCM (radio countermeasures), history 
of operational use 
see History of operational use 
RCM (radio countermeasures), person- 
nel training 
see Personnel training 
RCM (radio countermeasures), test 
methods and equipment 
see Test methods and equipment 
Receivers, 371-381 
autodyne for spot jamming, 288 
Bagful (recording receiver), 278-279, 
287, 299 

controlled-device, 380-381 


INDEX 


533 


direction-finding, 11, 210-212, 375- 
380, 457 

early-warning, 11, 205-206, 375, 413 
50 to 1000 me, 454 
for spot jamming, 177-178, 288 
homing, 206-207, 295, 376-377, 379- 
380 

monitoring, 10-11 

panoramic, 153-155, 204-205, 371 

scanning, 178 

search, 136-139, 203-205, 208-213, 
371-374 

Receivers, jamming vulnerability, 166, 
400-403 

AN/ARC-4; 193 
AN/SRW-2; 195 
AN/SWR-2; 402-403 
ARB, 402 
BA-348-R, 193 
BC-312-N, 193, 401-402 
BC-342-N, 193, 401-402 
BC-348-R, 401-402 
BC-603-D, 193-194, 400 
BC-624-A, 193, 400-401 
BC-625-A, 401 
BC-639-A, 193, 401 
BC-652-A, 193, 401-402 
BC-654-A, 193, 401 
BC-659-A, 401-402 
BC-659-B, 400 
BC-669-C, 193, 401-402 
BC-IOOO-A, 401 
recommendations, 195 
SCR-300-A, 193-194 
SCR-511-B, 402 
SCR-609-A, 193-194 
Recommendations for future research 
antijamming printing attachment, 
200 

communications ferrets, 150 
jammer alignment systems, 179 
multianode magnetrons, 50 
photomultiplier tube, 21 
radar antijamming modifications, 
262-263 

radio wave propagation, 128 
receiver vulnerability, 195 
scanning receivers, 178 
split-anode magnetron, 43 
Recording receiver (Bagful), 278-279, 
287, 299 

Rectification of noise, 88-90 
effect on output spectra, 450 
linear rectifier, 89 
modulated signal in noise, 91-92 
quadratic rectifiers, 90 
Reflectors 

see Corner reflectors; Window (radar 
confusion reflectors) 
Resistance-capacitance video filter for 
antijamming, 259 


Resnatrons, 51-53 
characteristics, 51 
design features, 51-52 
860 me tetrode, 52 
high-power oscillator-amplifiers, 422 
sealed-off type, 52-53 
tunable tetrode, 52 
X-124 and X-139 beam tetrodes, 428- 
429 

Resonant systems, parameters, 427 
Resonant systems, transmission lines 
analysis, 132 

mode separation in an ;oscillator, 
133 

resonant-line sections, 132, 446 
RF-9/UPT oscillator for practice jam- 
mers, 421 

R-f power indicator, 418 
R-f sweep generator, 414 
R-f voltage regulator, 454 
RG-21/AU coaxial cable, 446 
RHB (radar homing bomb), jamming 
susceptibility, 257, 404 
Ridge wave guides, 132, 448 
Ring transmitter (radar operator train- 
ing aid), 79 

RL (Radiation Laboratory) 

antijamming research and develop- 
ment, 249-260 

Squirrel-Cage magnetron, 39-41 
RLC filter for antijamming, 252 
Rope (electromagnetic- wave reflector), 
113-115, 237-240, 363-365 
balloon-supported, 411 
dispensers, 239-240, 364-365 
field tests, 411 
operation, 344 

production of vertically polarized 
radar echoes, 410 
response characteristics, 240, 363 
ribbon-shaped, 113 
Tinsel (Fishline), 238 
tuned, 115, 230-231, 237-238 
types, 232 

untuned, 230-231, 239-240 
use against EW radar, 359 
RP-347 spectrum analyzer, 69-70, 416 
RP-392 K spectrum analyzer, 417 
RRL 

see Radio Research Laboratory 
Ruffian (German bomber navigational 
aid), 264 

Rug (radar jammer), 384-385 
advantages, 384 
effectiveness, 304 

modifications for spot jamming, 457 
use against SLC radar, 361-362 

S-27D hallicrafter search receiver, 371 
Sawtooth frequency modulation, 106- 
107 


S-band antennas, 441 
SC radar, use in antijamming training, 
422 

Scanning receivers, 178 
SCR-268 radar 

antijamming modifications, 259 
detector video replacement units, 405 
jamming tests, 403 
susceptibility to jamming, 257 
SCR-296 radar, antijamming modifica- 
tions, 259 

SCR-300-A receiver, vulnerability to 
jamming, 193-194 

SCR-511-B receiver, jamming vulner- 
ability, 402 

SCR-521A radar, antijamming char- 
acteristics, 403 

SCR-522A search receiver, 371 
SCR-536 portable radiophone, operat- 
ing characteristics, 402 
SCR-545 radar, susceptibility to jam- 
ming, 257, 404 

SCR-591 spot jammer, 176-177 
SCR-609-A receiver, vulnerability to 
jamming, 193-194 

SCR-617 radar, antijamming character- 
istics, 403 

SCR-717B radar, antijamming char- 
acteristics, 259-260, 403, 406 
SCR-720A radar, jamming susceptibil- 
ity, 404 

SD-849 Squirrel-Cage magnetron, 426 
Search jammers, automatic, 181-182 
Beagle, 182 
Broom, 181-182, 393 
Search receivers, 9-11, 371-374 
antennas, 55, 126-127, 438, 440 
antijamming measures for, 408 
Bagful, 278-279, 287, 299 
Blinker, 287-288 
communications, 371 
design, 455-456 

for proximity fuze countermeasure, 
159 

jamming vulnerability, 193, 401 
microwave, 288, 420 
panoramic, 153-155, 204-205, 371 
pulsed, 371 

radar, 203-205, 208-213, 371-374 
range, 10 
requirements, 150 

suppression of spurious response, 150 
test transmitter, 414 
tuning units, 372-373 
Search receivers, theoretical studies, 
136-139 

comparison with experimental re- 
sults, 139 

ignoramus theory, 138-139 
monochromatic case, 137 
uncorrelated model, 137-139 


534 


INDEX 


Searchlight-control radar, countermeas- 
ures to 

see SLC radar (searchlight-control), 
countermeasures to 

Searchlight-control warning receiver, 1 1 
Setter (airborne direction-finding at- 
tachment), 375-376 
Shell-burst echoes, 245 
Ship echoes 

air-and sea-zone, 128 
operational considerations, 129 
parameters and formulas, 128-129 
Ship-borne antennas 
bandwidth, 55 
directivity, 55-56 
installation, 57 

method of obtaining patterns, 443 
models, 143, 442 
wave antenna, 64 

Ship-borne direction finder, 378, 379 
Ship-borne jammers, 185-187, 390-393 
AN/SRQ-1; 186-187, 392 
AN/SRQ-11; 183, 185 
Elephant, 228-229, 253-254, 300, 390- 
391 

MAS, 185-186, 392-393 
Model Tea, 64 
power requirements, 460 
Signal generators 
see Oscillators 

Signal visibility through noise, 91-99 
condition for visibility on oscilloscope 
screen, 98 

deflection modulation, 98-99 
effects of integration, 96-99 
intensity modulation, 98-99 
reception of radar signals, 93-96 
rectification of a modulated signal, 
91-92 

Signal-repeating systems 
broad-band, 455 
Peter Pan, 155-159, 381 
Piano, 182-183 

Silent Knight (blanking receiver cir- 
cuit), 373 

6D4 gas triode, 449-451 
clipping of noise output, 102, 450 
housing and magnet for noise source, 
23-25, 423, 450 
noise output, 449 
tube tester, 31 
use as noise source, 450-451 
6J21 tunable magnetron, 425, 428 
612 L multianode magnetron, 44 
Skirted stub antenna, 435 
SLC radar (searchlight-control), coun- 
termeasures to, 360-365 
Dina, 361-362 
jamming, 12 

jamming susceptibility, 257, 404 
operational problems, 352, 360-361 


Porcupines, 362-363 
Rope, 363-365 
Rug, 361-362 

SLC (searchlight-control) warning re- 
ceiver, 11 

Sleeve antennas, 65 
advantages, 443 
AS-181/APT, 435-436 
construction, 445 
impedance characteristics, 443 
radiation patterns, 443 
Slot antennas, 436-437 

modeling for pattern measurements, 
442 

wide-band, 444 
Sound analyzers 

General Radio, 30-31 
range extender, 451 
Spark jammers, 171-172 
expendable, 392 
theoretical efficiency, 382 
Specifications 

Chaff, 231, 408, 410 
guided missiles, jammers, 180 
magnetrons, 44-45 
noise sources for jamming, 19 
Spectral distribution of clipped noise, 
81, 84-87, 102 

Spectrum analyzers, 68-74, 415-417 
10-3500 me, 70-71 
100-1400 me, 68-70 
audio, 30-31 
crystal mixers, 416 
double superheterodyne type, 416 
for carrier frequencies, 416 
impedance bridge, 115-mc, 72 
low-frequency, 416 
narrow-band amplifier, 115-mc, 71 
OCC, 68-70 
panoramic, 415 
pulse analyzer, 414, 417 
RP-347; 69-70, 416 
RP-392 K, 417 
studies on crystals, 72 
summary of development work, 423- 
424 

sweeping local oscillator type, 71- 
73 

variable input impedance, 72 
video, 30, 416 

wide - band intermediate - frequency, 
73-74 

Speech-masking effectiveness of jam- 
ming, 393 

Speed-X buzzer (noise generator), 28 
Spinners, antenna, 377-378 
Spinning loop aircraft direction finder, 
380 

Split can antenna, 436, 439 
Split-anode magnetrons 
see Magnetrons, split-anode 


Spoofs, naval (seaborne corner reflec- 
tors), 459-460 
Spot jammers, 176-179 

airborne multiple jammer, 178, 
AN/ARQ-10 (SCR-591); 176-177 
Carpet, 275, 280, 385, 457 
Cigar, 389 

design considerations, 216 
evaluation, 168, 276 
MAS, 392 
Rug, 457 

Spot jamming techniques, 176-179 
alignment systems, 178-179, 397 
broad-band scanning technique, 178 
comparison with barrage jamming, 
168, 216 

continuous wave modulation, 164- 
165 

frequency modulation, 387 
frequency setting, 169, 219-221, 278- 
279, 393 

listening-through system, 177-178 
narrow-band receiver technique, 

178 

operational use, 345-346 
operator training, 79, 276 
receivers, 177-178, 288 
requirements, 176-177, 460 
selection of type, 168, 216, 221 
Spud (radar search receiver), 373 
Squirrel-Cage magnetrons, 39-41, 426- 
428 

Stardust (pulse repeater), 412 
Static burst jamming, 397 
Steel antenna, advantages, 443 
Step-tone jammer, effectiveness, 401 
Stingaree antennas, 445 
Stopwatch (automatic jammer align- 
ment system) 
design, 394 

recommendations for future research, 

179 

Stub antennas 

radiation patterns, 441 
skirted stub, 435 
thick stub, 433-434 
with series matching sections, 443 
Submarine direction-finding system, 
379 

Superheterodyne spectrum analyzer, 
416 

Sweep generator, wide-band r-f, 414 
SX-25 (communications receiver), use 
as noise analyzer, 420 
Sylvania Electric Products 

Squirrel-Cage magnetron, 39-41 
vacuum tube development, 39-53 

Tail (homing attachment for direction 
finders), 376 
Tank antennas, 433 


INDEX 


535 


Tape recorders, magnetic, 155-158 
AK/ARQ-12; 156-158, 380-381 
AN/SRQ-2; 156-158, 380-381 
use in Peter Pan jamming system, 
155-157, 381 

Targets, frequency sensitivity, 122-123 
TDY radar jamming transmitter, 214 
TDY rotating antenna, eft'ectiveness, 
342 

Teflon as insulator, 37 
Telegraphy jamming 
c-w telegraphy, 396 
effect on operators, 190 
effectiveness, 393, 395, 397 
teleprinters, 197 
teletype, 194, 401 
tests, 399-400 
types of interference, 190 
Test methods and equipment, 66-77, 
413-422 

Carpet checker, 418 
Carpet output indicator, 418 
communications receiver vulnerabil- 
ity to jamming, 66-68 
crystal probes, 76 
crystal rectifier voltmeter, 420 
double-peaking amplifier-alignment 
unit, 76 

frequency meters, 76, 78, 417-418 
high-frequency calorimetric watt- 
meter, 75, 418-419 
noise analyzer, 420 
noise tube tester, 419-420 
r-f power measurement, 418-419 
signal generators, 67-68, 413-415, 
420-422, 425-429 

spectrum analyzers, 30-31, 68-74, 
415-417, 424 

summary of types and applications, 
77-79 

test oscillators, 76, 420 
transmitter output indicator, 418 
u-h-f power meter, 418 
Thermal noise, jamming effectiveness, 
163-164 

Thermistor bridge, self-calibrating, 419 
Time and impulse code systems 
Beechnut, 198, 399 
Voflag, 198, 399 

Tinsel (modulation method), 172 
Tinsel Rope (radar deception device), 
238 

TPQ-T2 antijamming training set, 261- 
262, 421 

Trailing-wire antennas, 64-65, 443 
Training methods and equipment 
see Personnel training 
Transformer design 
Bazooka, 433 

broad-band wave guide-to-line junc- 
tion, 134 


cores, 33, 36-37 
eddy-current loss, 454 
for noise jamming, 102-104 
for 100 to 3000 me, 453-454 
for radio power supplies, 453 
ideal load, 133 

performance of matching sections, 

133 

series of quarter- and half-wave sec- 
tions, 134 

skin depth, 102-104 

synthesis of matching sections, 134 

video, 32-38, 454 

wide-band balancing transformer, 134 
Transformers, noise 

see Video noise transformers 
Transmission lines, applications, 131- 
135 

antennas, 58 

design of matching transformers, 133- 

134 

filters, 134-135 
properties, 131-132 
radar countermeasures, 63 
resonant circuits and systems, 132-133 
velocity of propagation in coaxial 
line, 132 

Transmitter for checking operation of 
search receiver, 414 
Transmitter output indicator, 418 
Transmitters, jamming 
see Jammers 

TS-53/AP Carpet checker, 418 
TS-54/AP spectrum analyzer 

graphical representation of function- 
ing, 73-74 

power output of video amplifier, 74 
resolving power, 73-74 
TS-92/AP bandwidth adjustment indi- 
cator, 417 

TS-99/AP heterodyne frequency meter, 
417 

TS- 109/SPA interference generator, 79, 
261-262, 420-421 

TS-118/AP radio-frequency power in- 
dicator, 418 

Tuba (ground-based jammer), 390-391 
countermeasure to AI radar, 140 
operational use, 300-302 
Tube development 

see Electron tube development 
Tube tester, noise, 31 
Tubes, gas 

see Gas tube noise sources for jam- 
ming 

Tungar bulbs, use as noise generators, 
452 

Tuning units for radar search receivers, 
372-373 

Turnstiles (confusion reflector), 230- 
231, 238-239 


2C4 gas triode, noise output, 449 
2D21 gas tetrode, noise output, 450 
2K28 u-h-f oscillator, 429 
2K48 local oscillator tube, 40-41 
2K49 local oscillator tube, 40-41 
233A airborne transceiver, jamming 
vulnerability, 401 

2050 gas tube for noise jamming, 450 

U 400 tube tester, 31 
U-1500 pulser (signal generator), 414- 
415 

U-h-f (ultra-high-frequency) antennas, 
444 

U-h-f (ultra-high-frequency) filters 
design equations and performance 
curves, 452 

mechanical design, 453 
U-h-f (ultra-high-frequency) oscillators 
see Oscillators, ultra-high-frequency 
U-h-f (ultra-high-frequency) power me- 
ter, 418 

U-h-f (ultra-high-frequency) resonant 
systems, parameters, 427 
University of California, resnatron, 51 

Vacuum tube development 
see Electron tube development 
V-antennas, 64 

Velocity- modulationtube, magnetically- 
focused, 426 

V-h-f (very-high-frequency) homing 
systems, 377 

V-h-f (very-high-frequency) radar 
screen, 295 

Vicalloy recording tape, 157 
Video amplifiers for antijamming, 406 
Video analyzer, radar, 391 
Video filter for antijamming, 259, 405 
Video noise generators 

constriction oscillator, 25, 451 
6D4 noise unit, 23-25 
Video noise transformers, 32-38 
core losses, 34 
core materials, 33 
design, 36-38, 454 
impedance measurements, 33 
tests, 37-38 

Video spectrum analyzer, 30, 416 
Visual detection of radar signals 
evaluation, 431-432 
sensitivity, 95 
signal-to-noise ratio, 93-94 
Voflag (code system), 198, 399 
Voice substitute systems, 197-200 
antijamming characteristics, 198-200, 
399 

impulse and time code systems, 198 
teleprinters, 197 

Voice-frequency noise generator, 451 
Voltage regulator, r-f, 454 


536 


INDEX 


Voltmeter, crystal rectifier, 420 
Voltmeter, noise-measuring, 31, 451 

Walkie-talkies, jammer for, 382 
Warning receivers, 205-206 
Boozer, 206, 287, 299 
circuits, 213 
gun-laying radar, 1 1 
purpose, 11 
searchlight control, 11 
test buzzer, 414 
time element, 206 
Zero Catch II; 375 

Wattmeter, high-frequency calorimet- 
ric, 418-419 

coaxial line sections, 75 
microwave, 419 
water-load type, 419 
Wattmeter, waveguide, 448 
Wave analyzer, 30-31 
Wave antennas 

Beverage wave antenna, 64 
comparison with vertical radiators, 444 
measurements over sandy soil, 444 
Wave guides 
antennas, 434 

directional pickup and wattmeter for 
guides, 448 
dummy antenna, 448 
installation, 447 
moisture in guides, 447, 448 
properties, 131-132 
ridge guides, 132, 448 
use of resonant probe, 447 
wide-band mixers, 447 
Waveguide output magnetrons, 425 
Wavemeter, 417-418 
Westinghouse Research Laboratories, 
vacuum-tube development, 39- 
53, 427 

Whip antennas, 440-441 
Window (radar confusion reflectors), 
110-123, 230-245, 408-412 
Angels, 116-117, 230-231, 241-243, 
411-412 


Birdnesting phenomena, 231 
Chaff, 111-113, 232-237, 273-275, 
408-410 

countermeasures to, 117-122, 253-254 
field tests, 412 
operation, 13 
pulse length, 117 

Rope, 113-115, 237-240, 363-365, 410 
squares or sheets, 244 
tuned and untuned, 230-231 
Turnstiles, 230-231, 238-239 
types, 230-231 
use in bombs, 409 
Wing antennas, 65 
Wurzburg (German radar) 
antijamming devices, 457 
frequency range, 234 
Wurzburg simulator, 406-407 


X-124 and X-139 resnatrons, 428-429 
XA-2 airborne jammer for radar, 228 
X-band jammers 
test jammer, 415 
use of A- 131 magnetron, 425 
XN-1 magnetic tape recorder, 156-158 


Z-668 reflex klystron, 71 
Zero Catch II (early-warning radar re- 
ceiver), 375 

ZP-522 c-w oscillator, 428 
ZP-572 lighthouse triode, 41 
ZP-579 split-anode magnetron 
characteristics, 40, 43 
design and performance, 422 
efficiency, 423 

ZP-584 split-anode magnetron, 40, 43 
ZP-590 split-anode magnetron 
characteristics, 40 
electron escape, 42 
frequency range, 43, 45 
ZP-594 multianode magnetron, 424 
cathode, 49 
characteristics, 44 


ZP-595 split-anode magnetron, 50-51 
characteristics, 51 
construction, 422 
modification, 51 
ZP-597 multianode magnetron 
cathode, 49 
characteristics, 44 
noise modulation, 427 
parasitic resonance, 424 
ZP-599 split-anode magnetron, 44, 45 
ZP-612 multianode magnetron, 46-50 
cathode, 48 
characteristics, 44 
response to noise modulation, 428 
tuning method, 47-48 
wave-guide transformer, 46, 49 
ZP-615 multianode magnetron 
cathode, 49 
characteristics, 44 
tuning structure, 49 
ZP-616 multianode magnetron, 424 
characteristics, 44 
construction, 49 
tuning method, 48 

ZP-633 split-anode magnetron, 40, 43, 
423 

ZP-636 split-anode magnetron 
characteristics, 51 
construction, 50 
design, 423 

Z P-639 multianode magnetron, 44, 49 
ZP-646 split-anode magnetron 
characteristics, 40, 43 
electron escape, 42 
Z P-647 neutrode magnetron, 43-45 
characteristics, 44 
frequency range, 45 
ZP-652 magnetron, 40, 424 
ZP-666 split-anode magnetron, 40, 43 
ZP-675 neutrode magnetron, 40, 43 
ZP-676 neutrode magnetron, 40, 43, 45 
ZP-677 neutrode magnetron, 43 
ZP-685 neutrode magnetron, 43-45 
ZP-693 multianode magnetron, 44 
ZP-838 multianode magnetron, 44 


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